Memorias Curso en Cirugía Tejidos Blandos, Dr. Erick Monnet

AMMVEPE 1968 - 2014

MEMORIAS CURSO DE CIRUGÍA AVANZADA EN TEJIDOS BLANDOS, DICIEMBRE 2014 “DR. ERIC MONNET”

Asociación Mexicana de Médicos Veterinarios Especialistas en Pequeñas Especies, S. C. www.ammvepe.com.mx

Asociación Mexicana de Médicos Veterinarios Especialistas en Pequeñas Especies, S. C. www.ammvepe.com.mx

Asociación Mexicana de Médicos Veterinarios Especialistas en Pequeñas Especies, S. C. www.ammvepe.com.mx

Eric Monnet, DVM, PhD, FAHA Diplomate ACVS and ECVS Colorado State University, Fort Collins, Colorado

Actualmente es profesor en cirugía de animales pequeños (tejidos blandos) en la Universidad del Estado de Colorado.

El Dr. Monnet fue presidente fundador en 2001 - 2003 de la Sociedad Veterinaria para la Cirugía en Tejidos Blandos y de la Sociedad de Endoscopia Veterinaria.

Es editor de los libros de texto; “Mecanismos de Enfermedad en la Cirugía de Animales Pequeños” (Disease Mechanisms in Small Animal Surgery 3rd. edition) y la primera edición del libro “Cirugía de Tejidos Blandos en Animales Pequeños” (Small Animal Soft Tissue Surgery).

Parte de sus actividades y habilidades personales son; la Cirugía, Medicina Veterinaria, Investigación Clínica, Enseñanza Universitaria, Investigación y Diseño, Conferencias y presentaciones, Biotecnología, Estadística, Fisiología, Experimentación, Enseñanza Académica, Escritor científico.

Dr. Eric Monnet

PERFIL PROFESIONAL

El Dr. Eric Monnet es graduado de la Escuela de Veterinaria en Maisons Alfort, Francia en 1985.

Trabajó por cuatro años en Paris, realizando práctica privada en medicina y cirugía en animales pequeños.

En 1994, el Dr. Monnet completó una residencia en la Universidad del Estado de Colorado relacionada a cirugía en animales pequeños, y últimamente ha terminado una Maestría en Ciencias.

En 1997, el Dr. Eric Monnet recibió su Doctorado en Ciencias Clínicas estudiando la eficiencia cardiaca en perros.

En el año 2003, llega a ser miembro de la Asociación Americana del Corazón (American Heart Association).

Asociación Mexicana de Médicos Veterinarios Especialistas en Pequeñas Especies, S. C. www.ammvepe.com.mx

INDICE GENERAL CÓMO REALIZAR CIRUGÍA GASTROINTESTINAL DE FORMA SEGURA DILATACIÓN Y VOLVULO GÁSTRICO PERITONITIS CIRUGÍA DEL HÍGADO Y VESÍCULA BILIAR TRATAMIENTO QUIRÚRGICO DE LOS CÁLCULOS URINARIOS CIRUGÍA DEL PÁNCREAS PARÁLISIS LARINGEA SÍNDROME DEL BARQUICEFÁLICO LAPAROSCOPIA EN LA PRÁCTICA DE PEQUEÑAS ESPECIES TORACOTOMÍA Y TORACOSCOPÍA CIRUGÍA PULMONAR EFUSIÓN PLEURAL PERSISTENCIA DEL DUCTO ARTERIOSO

Asociación Mexicana de Médicos Veterinarios Especialistas en Pequeñas Especies, S. C. www.ammvepe.com.mx

PRINCIPLES OF GASTROINTESTINAL SURGERY How to perform a safe gastrointestinal surgery?

Eric Monnet, DVM, PhD, FAHA Diplomate ACVS and ECVS Colorado State University, Fort Collins, Colorado Gastrointestinal surgery is performed very commonly in small animal for biopsy, removal of a foreign body, upper gastrointestinal bleeding, resection of a non-viable segment of intestine, resection of non-viable portion of the stomach, and resection of a neoplasia. Gastrotomy, gastrectomy, enterotomy, and enterectomy are the procedures routinely performed. General principles common to all of these procedures have to be followed.

Peritonitis is life threatening complication that can happen in 13 to 20% of the cases.

To reduce the risk of peritonitis it is important to minimize the trauma to the tissue and to recognize the tissue viability. Peritonitis can develop in the immediate post-operative period because of severe contamination during the surgery or leakage of the suture line.

Leakage happens if the tissue are not viable or when the surgical technique was not appropriate.

Peritonitis can happen also 3 to 4 days after surgery at the peak of debridement. Dehiscence of an anastomosis happened because the debridement phase goes beyond the suture line. If the tissue handling or the surgical technique were not appropriate, the debridement will be exacerbated and dehiscence can occur.

ANTIBIOTIC PROPHYLAXIS Gastrointestinal surgery without a peritonitis is considered as a clean-contaminated surgery. Therefore antibiotics are required during the procedures. Most common bacteria encountered during gastrointestinal surgery are: Escherichia coli, Enterococcus spp, Streptococcus, Staphylococccus aureus, Proteus, and Bacteroides fragilis.

In the stomach, the bacteria population is more limited than in the rest of the intestine because of the acidic environment. In the colon the population of anaerobic bacteria is elevated.

Before surgery the patient is placed on prophylactic intravenous antibiotic. For the surgery of the stomach, ampicillin or first generation cephalosporin (20 mg/kg IV every 60 min) can be used. For the rest of the intestine, second generation antibiotics are preferable because they a have a broad sprectrum against gram + and -. Cefoxitin (20 mg / kg IV every 90 min) is the antibiotic of choice. A combination of ampicillin enrofloxacin can be used also especially if a peritonitis is present. Antibiotics are interrupted at the end of the procedure unless the animal has peritonitis. The animals need to be watch closely for signs of infection.

CHOICE OF SUTURE MATERIAL AND NEEDLES A wide range of suture materials has been used during gastrointestinal surgery. It is recommended to use synthetic absorbable monofilament suture materials. Synthetic absorbable sutures are absorbed primarily by hydrolysis, which is very predictable.

Monofilament sutures are less traumatic than braided sutures when they are placed through the wall of the gastrointestinal tract. However, they have more memory which makes them harder to work with.

A monofilament suture size 4.0 or 3.0 is recommended for gastrointestinal surgery. A small suture material will more likely trigger less inflammation. Glycomer 631 (Biosyn) or Monocryl are a very good choice since it retains 50% of its tensile strength for 3 weeks. A taper needle is recommended for placement sutures in the stomach wall and the intestine because it does not cut the fibers of collagen.

SUTURE PATTERN The gastrointestinal tract is closed with a simple continuous suture pattern to provide apposition of all the layers of the wall of the gastrointestinal tract. It is important to place the suture full thickness to make sure the submucosa is incorporated. This suture technique will provide primary healing of the wall of the gastrointestinal tract. When a simple continuous pattern is used it is recommended to place the first and the last stitches with knots outside the incision because it may provide a very good seal. When the sutures are placed it is important to avoid to traumatize the wall of the gastrointestinal tract. It is then better not to grab the wall the gastrointestinal with grasping forceps as much as possible. When the sutures are placed it is important to follow the curvature of the needle to reduce trauma to the soft tissue.

ASEPSIS Every effort should be made to prevent contamination of the abdominal cavity during gastrointestinal surgery. The stomach or the loop of intestine are “packed off� the rest of the abdominal cavity. Layers of moist laparotomy sponges are used. Intestinal content is moved away for the surgical site with gentle manipulation and atraumatic clamps are placed to prevent the intestinal content to come back. Stay sutures are placed in the stomach to elevate the stomach wall and prevent spillage of stomach content into the peritoneal cavity.

After completion of the surgery, the peritoneal cavity is lavaged with warm sterile saline solution to removed gastrointestinal spillage and blood clots. Usually 1 liter of saline is used for a 10 kg dog. The entire fluid is eliminated with surgical suction to get the peritoneal cavity as dry as possible.

Gloves and instruments are then changed. New surgical towels are placed on the edges of the laparotomy. The abdominal cavity is then closed routinely.

ASSESSMENT OF VIABILITY Stomach No objective criteria exist to evaluate the gastric wall viability. Absence of peristaltic wave, pale greenish to gray serosal color, thin gastric wall, and lack of bleeding after partial thickness incision are signs of gastric wall devitalisation.

Intestine Viability is assessed by coloration of the serosa, peristalsism, pulse in the jejunal arteries, and utilization of intravenous fluorescein. Fluorescein at the dose of 15 mg/kg is injected intravenously. Fluorescein emits a gold green fluorescence when exposed to ultraviolet light. Viable intestine has a smooth uniform green gold fluorescence.

Hyperemic intestine has a brighter color than normal. Non viable intestine has patchy fluorescence or no fluorescence. The fluorescence can also be located around blood vessel.

SURGERY OF THE STOMACH Gastrotomy Gastrotomy incision is performed in a relatively avascular area, midway between the lesser and the greater curvature of the stomach. One stay suture is placed at each end of the planed gastrotomy incision. Stay sutures are used to manipulate the stomach and bring the stomach wall to the edge of the abdominal incision. The stomach is walled off with moist laparotomy sponges to prevent contamination of the abdominal cavity with gastric content. An 11 blade is used to stab the gastric wall next to one stay suture. Then, a Metzembaum scissors is used to extend the gastrotomy incision. The incision should be long enough to remove the foreign body without tearing the stomach wall. Hemorrhage occurs mainly in the seromuscular layer and can be controlled by ligation with fine absorbable sutures.

The foreign body is extracted and the gastrotomy closed.

Gastrotomy is closed with one layer simple apposition pattern with 3-0 monofilament absorbable suture. The abdominal cavity is lavage with warm saline prior to closure.

Surgical gloves are changed and a new pack of instruments is then used to complete the abdominal closure.

Gastrectomy Gastrectomy is required to resect the non viable part of the stomach wall during GDV, or resection of an ulcer or a neoplasia. Stomach wall resection for a gastric ulcer requires wide margin since gastric ulceration could be associated with gastric adenocarcinoma or gastric lymphoma.

Two options are available: gastrectomy with either traditional suture technique or stapling suture. Gastrectomy with automatic stapling equipment is associated with the best post surgical outcome during GDV. This is the recommended technique.

Gastrectomy during GDV Branches of the short gastric arteries and left gastro-epiploic artery supplying the area to be resected are ligated. Non-viable gastric wall is resected with Metzembaum scissors to the level of healthy gastric tissue. Closure with suture material is possible. This technique is associated with 60% mortality. If autostapling equipment is available a Thoraco-Abdominal device (TA 55 or 90) can be used to perform the gastrectomy (Figure

1). The TA 55 or 90 placed two staggered row of staples respectively 55 or 90 mm long.

The length of staples for stomach wall resection should be 4.8 mm. The TA 55 or 90 is first clamped on healthy stomach wall. The two row of staples are then fired and a 15 blade is used to resect the devitalized stomach wall. The TA is then released.

The suture line is then inspected to be sure that all the staples are in correct position and then a simple inverting suture line is applied. The advantages of Figure 1 this technique include decrease surgical time and decreased abdominal contamination from gastric spillage.

Mortality rate with the autostapling equipment is close to 10%. Stomach rupture at the time of surgery is associated with severe peritonitis.

Gastrectomy for ulcer or mass.

After identification of the stomach ulcer or tumor, the healthy stomach is retracted with stay sutures to prevent gastric spillage. The stomach wall is then resected around the lesion. The stomach wall is highly vascular. Bleeding blood vessels on the line of incision are ligated with 4.0 monofilament absorbable sutures. Staples can be used to close the gastrectomy. Hand suture can be performed if stapling equipment is not available. Two inverting continuous sutures have been used to close the stomach after gastrectomy. A Cushing suture followed by a Lembert is the traditional technique.

However, one simple continuous apposition suture can be used to close the stomach.

SURGERY OF THE INTESTINE Enterotomy A variety of foreign bodies can be ingested by young animals. Linear foreign bodies are more common in cats. Once, an object has passed through the pylorus, the next smallest lumen are the distal duodenum and the proximal jejunum.

Plication of the intestinal indicates the presence of a linear foreign body. Usually one end of the linear body is still located in the stomach and need to be released first.

Particular attention is paid to mesenteric border especially with a linear foreign material.

Linear foreign body can cut through the mesenteric border and induce leakage of intestinal content. Multiple enterotomy may be required to remove the entire linear foreign body. Enterectomy is required if the mesenteric border has been damaged.

Enterotomy is performed immediately distal to the foreign material. Intestine is walled off the abdominal cavity to prevent leakage of intestinal content inside the abdominal cavity. The incision on the antimesenteric border should be long enough to extract the foreign body without tearing the intestine.

The enterotomy is then closed with a simple interrupted appositional pattern with 4-0 monofilament absorbable suture. Since the submucosa is the only holding layer, it needs to be incorporated in the suture. The submucosa tends to retract away from the edge of the incision. The everted mucosa can be trimmed away to allow better exposure of the submucosa.

A serosal patch can be performed to improve blood supply to the enterotomy site and increase its tensile strength. The abdominal cavity is lavage with warm saline prior to closure. Surgical gloves are changed and a new pack of instruments is then used to complete the abdominal closure.

Enterectomy An enterectomy is indicated if the intestine is not viable (intussusception, volvulus) perforated by a linear foreign material at the mesenteric border, or if a intestinal neoplasia Figure 2 is present. End to end anastomosis is the preferred technique to perform an enterectomy.

Intestine is walled off the abdominal cavity to prevent leakage of intestinal content inside the abdominal cavity.

Enterectomy requires double ligation of the branches of the arterio-venous supply of the portion of intestine to resect (Figure 2).

The terminal arcade is also double ligated. Transection is performed between the double ligations. Crushing clamps are then placed on the portion of intestine that is going to be resected.

Figure 3 The clamps are either placed perpendicular or at a slight angle toward the normal intestine. Noncrushing clamps are placed on Figure 4 the normal intestine 4 to 5 cm away from the enterectomy site after milking away the intestinal content.

The intestine is transected with a scalpel blade using the crushing clamps as guide. Since the submucosa is the only holding layer, it needs to be incorporated in the suture. The submucosa tends to retract away from the edge of the

incision. The everted mucosa can be trimmed away to allow better exposure of the submucosa (Figure 3). Anastomosis is performed with simple interrupted or continuous appositional pattern with 4-0 monofilament absorbable suture (Figure 4).

If the two extremities of the intestine are not of equivalent diameter the smaller diameter segment can is incised on the antimesenteric border to create a larger spatulated edge (Figure 4). A serosal patch can be placed around the enterectomy site to improve blood supply and tensile strength.

The abdominal cavity is lavage with warm saline prior to closure. Surgical gloves are changed and a new pack of instruments is then used to complete the abdominal closure.

POSTOPERATIVE MONITORING Postoperatively the patients should be monitored for signs of peritonitis, hypotension, disseminated intravascular coagulation, and pain. Patients can be fed 8 hours after surgery unless the patients is vomiting. Feeding tubes might be required to support those patients. Peritonitis occurs in 13 to 20% of the cases. Leakage after gastrointestinal surgery can happen within 24 hours of surgery because of non viable tissue or inappropriate surgical technique. It can also happen 3 to 4 days after surgery at the peak of the debridement phase. Clinical signs of peritonitis will be tachycardia, tachypnea, acute abdominal pain, hypoglycemia, and hyperthermia. An abdominocenthesis is then required to confirm the presence of bacteria in the abdomen. If bacteria are presented pass 8 hours after surgery, the anastomosis is leaking and a second surgery is required.

GASTRIC DILATATION VOLVULUS SYNDROME Eric Monnet, DVM, PhD, FAHA Diplomate ACVS and ECVS Colorado State University, Fort Collins, Colorado Gastric dilatation volvulus syndrome is an acute medical and surgical condition due to several pathophysiological effects occurring secondary to gastric distension and mal-positioning.

It occurs most commonly in large, deep chested dogs. Gastric dilatation volvulus should be differentiated from food engorgement. Food engorgement results from the over consumption of food and can result in severe dilation of the stomach. Large and giant breed dogs appear to have a 7% risk of death from GDV throughout their lifetime. Great Danes, however, have a 42.4% chance of developing GDV, and a 12.6% chance of dying from GDV in their lifetimes.

Chronic gastric dilatation volvulus has been recognized at several occasions in dogs. The diagnosis is more subtle because the clinical signs are not as dramatic as for an acute gastric dilatation volvulus. Dogs with chronic dilatation volvulus have an history of chronic vomiting, flatulence, and weight loss.

Aerophagia is the most likely source of gas accumulation. Bacterial fermentation of carbohydrate, gas production from acid-bicarbonate reactions may contribute to gas accumulation. The fluid component of gastric contents is a combination of ingesta, gastric secretions, and transudate from venous obstruction.

The mechanism of gastric outflow obstruction is unknown. As gastric dilatation progresses, the normal means of relief, such as eructation, vomiting, or pyloric emptying fail to occur.

Pyloric function seems to be normal in dog treated for gastric dilatation volvulus. Acute gastric dilatation volvulus has been recognized for many years in dogs however its exact cause is still not clearly understood in dogs. Only risk factors have been identified. Increased gastrin level, decreased stomach motility and delayed gastric emptying have been mentioned as a risk factor but never been demonstrated. Diet, the amount of food ingested, the frequency of feeding, behavior (fast eating style), exercise and stress after a meal are contributing factors for the development of gastric dilatation volvulus. Large breed dogs (Great Danes, Irish Setter, Standard Poodle, Weimaraner, Labrador, Golden Retreiver), dogs with large thoracic depth-towidth ratio, dogs of history of GI disease, dogs with family history of GDV, underweight dogs, and older animals are at higher risk to develop a gastric dilatation volvulus. Dogs with an happy personality might be at less risk.

The pyloric antrum rotates in a clockwise fashion. Displacement of the pylorus occurs from right toward ventral midline, passing along the gastric fundus and body to an area along the left abdominal wall close to the lower esophageal sphincter. At the same time the fundus goes in a ventral direction toward the right abdominal wall. Because of the attachment of the omentum to the greater curvature of the stomach, the omentum covers the stomach after volvulus. The displacement of the spleen may vary from the degree of volvulus. The spleen is usually engorged or can undergo torsion on its own pedicle. Thrombosis of the splenic artery can also occur. Most commonly 1800 degree of rotation is seen but 3600 rotation is possible.

Gastric dilatation causes compression of the caudal vena cava and portal vein. Sequestration of blood in the spleen, kidney, and gastrointestinal tract occurs. Compression of the caudal vena cava and portal vein induces a decreased venous return resulting in hypovolemic shock.

Hypotension and venous stasis result in cellular hypoxia and anaerobic metabolism. Focal myocardial ischemia and hypoxia will reduce contractility and induce arrhythmias. Vascular stasis, hypoxia and acidosis can predispose to the development of disseminated intravascular coagulopathy. Respiratory dysfunction results from decreased pulmonary compliance and mechanical restriction of diaphragmatic movement by a dilated stomach. Tissue hypoxia results from decreased cardiac output and respiratory impairment. Increased gastric intraluminal pressure, portal hypertension, and venous stasis with thrombosis result in gastric mucosa stasis, hypoxia, and edema. Gastric wall necrosis can then develop in the fundus along the greater curvature Vascular wall disruption results in mucosal hemorrhage. Avulsion of branches from the short gastric arteries contributes to the blood loss, hypovolemia, and restriction of blood flow to the stomach.

CLINICAL SIGNS Dogs with gastric dilatation volvulus are presented with progressive distension and tympanic cranial abdomen. They are restlessness, retching, and hypersalivating. Weak peripheral pulse, pale mucous membrane, increased heart rate, prolonged capillary time, and tachypnea are present too. Abdominal pain is usually not present on palpation.

Dogs with a gastric dilatation volvulus are presented with a weak femoral pulse, increased heart rate, pale mucous membrane, decreased capillary refill time, and tachypnea. Dogs present clinical signs similar to hypovolemic shock because their venous return is limited by the stomach dilation. If decompression is not performed rapidly they can develop septic shock during to congestion and ischemia of the gastrointestinal tract.

DIAGNOSIS Very often the diagnosis is made from the history, the signalment and the physical examination. Radiographic evaluation is rarely required for the diagnosis of gastric dilatation volvulus.

Dogs are usually presented for unproductive vomiting, retching and hypersalivation. The abdomen is distended and as the severity increases the animal can become weak, lateral recumbent with tachypnea.

Signalment Gastric dilatation volvulus is most commonly seen in large and giant breed dogs. It also can be seen in small dogs and cats. Dogs from 10 month to 14 years old have been diagnosed with gastric dilatation volvulus. No sex predilection have been demonstrated.

Physical examination On physical examination is classic to find a large distended abdomen. On percussion, a tympanic sound is produced.

Abdominal palpation could be uncomfortable.

Animals hypersalivate and are retching.

Gastric dilatation volvulus induces different degree of shock that needs to be recognized during the evaluation of the patient. First, the animals are presented with clinical signs similar to hypovolemic shock because most of their blood volume is restricted in the caudal vena cava and the portal vein. Therefore, the animals are going to be tachycardic and tachypnic with a normal femoral pulse, a slow capillary refill time, pale mucous membrane, and cold extremities. With progression of the syndrome, the patients are going to go in endotoxemic shock with tachycardia, tachypnea, weak femoral pulse, injected mucous membrane, fever, slow capillary refill time.

Finally the patients are going to decompensate with severe hypotension, bradychardia, hypothermia, white mucous membranes and cold extremities.

The severity of the presentation is indicator of survival for the patients. Dogs that are presented bright and alert have better prognosis than dogs that lateral recumbent.

Blood work Complete blood count and biochemistry profile are indicated for dogs with GDV. Coagulation profile might be required for dogs with advance shock because of the increased risk of DIC in those patients. If the platelet count is low on the CBC it is also indicated to evaluate the coagaulation profile Lactate level needs to be evaluated too. Since dogs with GDV are in some degree of shock, very often they are presented with an elevated lactate level. It is important to evaluate the level of lactate at the time of presentation and after initiation of fluidotherapy. Response to medical is an important prognosis indicator. If the lactate level decreased by 50% after initiation of medical treatment the prognosis is good.

Radiographs Radiographs help to differentiate between gastric dilation and gastric dilation volvulus syndrome. Radiographs if necessary for the diagnosis are not performed until the patient is stable. Since the pylorus is displaced on the left side of the abdominal cavity in a dorso-cranial position to the fundus a right lateral recumbency radiographs are required to be able to have a double bubble image. The two bubbles are due to the accumulation of air in the pylorus and the fundus. Free gas is present in the abdomen when the stomach has ruptured.

If only gastric dilatation is present without volvulus, radiographs show a dilated stomach with dilated loop of jejunum.

Radiographs will also help differentiate between gastric dilatation volvulus and mesenteric volvulus. Dogs with mesenteric volvulus have very large loop of jejunum lined up parallel to each other.

TREATMENT Emergency treatment Emergency medical treatment of the hypovolemic shock and gastric decompression is required before surgical treatment for gastric dilatation volvulus. Venous catheters of the largest size possible are placed in the cephalic or jugular vein to deliver shock dose of intravenous fluid.

Isotonic fluids are delivered at an initial rate of 90 ml/kg during the first 30 to 60 min. The rate and volume of fluids administered can be adjusted according to assessment of several clinical

parameters: heart rate, pulse, mucous membrane, capillary refill time and measurement of central venous pressure. It is very common to start with a quarter of the total shock dose and evaluate the response of the patient. Colloids at the dose of 4 ml/kg are recommended during hypovolemic shock treatment. Blood gas and electrolyte evaluations are required before acidbase and electrolyte imbalances corrections are attempted. A dog presented with a gastric dilatation volvulus can be either alkalotic or acidotic, hypokalemic or normokalemic.

Gastric decompression is attempted first with an orogastric tube after initiation of fluid therapy. Patients' compliance, the amount of gastric distension, and the degree of gastric volvulus determine the ease and feasibility of passing a tube. Difficulties or easiness to pass a tube does not have a diagnostic value for the magnitude of the volvulus. Perforation of a compromised stomach can happen with orogastric tube. Measurement from the chin to the xiphoid before introduction of the tube may help prevent perforation of the stomach. If the intubation is successful stomach lavage is required to empty the stomach. Color and content of the fluid coming back after stomach lavage need to be looked at. Hemorrhagic fluid or black necrotic fragments are indications of stomach wall necrosis. To help intubation, it could be beneficial to place the dog in an upstanding position on its hind leg. If intubation is not successful, percutaneous gastrocentesis with 18 gauge needles is an option to decompress the stomach. Percutaneous gastrocentesis is performed on the right side. Abdominal contamination is a risk after percutaneous gastrocentesis especially if large trocars are used. After percutaneous gastrocentesis orogastric intubation can be tried again.

Cardiac rhythm needs to be evaluated before surgery. Supraventricular tachycardia and ventricular tachycardia are the most common arrhythmias associated with a gastric dilatation volvulus. Atrial fibrillation has been reported in some dogs with GDV without cardiomyopathy.

Usually the arrhythmias occur postoperatively. Twenty-five percent of dogs presented for gastric dilatation volvulus already have cardiac arrhythmias.

Surgical intervention is required after medical stabilization of the patient. Surgical intervention is recommended as soon as possible. Delayed surgery increased the potential for gastric wall edema and necrosis, and venous stasis especially if the stomach is rotated 360o. If the surgery is delayed potential cardiac arrhythmias can develop. Seventy-five percent of the dogs that have arrhythmias develop them 36 hours after the gastric dilatation episode. Delaying surgery increases the risk of stomach necrosis. It has also been shown that dogs with more than 5 or 6 hours of clinical signs related to GDV have a poor prognosis.

SURGICAL TREATMENT The purpose of the surgery is to derotate the stomach, evaluate the stomach wall and the spleen for ischemic injury, and perform a gastropexy. Gastropexy decreases the chances of recurrence from 80% to 5%. Dogs after a gastropexy can still dilate but not rotate their stomach.

The dogs are placed on dorsal recumbency and a midline celiotomy is performed. The surgeon stays on the right side of the dog. Upon opening the abdominal cavity, the omentum is covering the stomach which confirmed the diagnosis of gastric dilatation volvulus. The stomach can be decompressed again before derotation with a large orogastric tube. After identification of the pylorus and the fundus with a clockwise rotation, the pylorus is grasped with the right hand

and pulled ventrally toward the abdominal incision while the left hand pushed the fundus dorsally into the abdominal cavity. The spleen follows the motion of the stomach. If a splenic torsion is present a splenectomy is performed without untwisting the vascular pedicle.

After derotation, the stomach and spleen are evaluated for ischemic injuries. Usually the spleen shows signs of venous congestion that resorb quickly after derotation of the stomach.

Splenectomy is indicated if thrombosis of the splenic artery is present. Evaluation of gastric wall perfusion is difficult. Approximately 10% of dogs have a devitalized gastric wall requiring gastrectomy. Ischemic injury occurs most commonly in the fundic area along the greater curvature. No objective criteria exist to evaluate the gastric wall. Absence of peristaltic wave, pale greenish to gray serosal color, thin gastric wall, and lack of bleeding after partial thickness incision are signs of gastric wall devitalisation. Gastrectomy is required to resect the necrotic stomach wall. Two options are available: gastrectomy with either traditional suture technique or stapling suture.

The stomach is packed off from the abdominal cavity with multiple moistened laparotomy sponges. The healthy stomach is retracted with stay sutures to prevent gastric spillage. Branches of the short gastric arteries and left gastroepiploic artery supplying the area are ligated. Necrotic gastric wall is resected with Metzenbaum scissors to the level of healthy gastric tissue. A two layers closure with inverting pattern using 3-0 absorbable monofilament suture is necessary to close the stomach. This technique was associated with a 60% mortality. If autostapling equipment is available a Gastro-Intestinal Anastomosis device (GIA 50) or a Thoraco-Abdominal device (TA 90) can be used to perform the gastrectomy (Figure 1). Advantages of this technique include decrease surgical time and decreased abdominal contamination from gastric spillage.

Mortality rate with the autostapling equipment is close to 10%. Stomach rupture at the time of surgery is associated with severe peritonitis. Placement of a close suction drain is recommended to help control the peritonitis.

After gastrectomy, a gastropexy is required. A belt loop gastropexy, a circumcostal gastropexy and an incisional gastropexy are the most commonly performed with similar outcome. The circumcostal gastropexy is probably more technically demanding than any other technique. It is also associated with a risk of pneumothorax if the diaphragm is incised.

For a belt loop gastropexy (Figure 2), two small transverse stab incisions are made in the parietal peritoneum and transverse abdominalis muscle. The incisions are located 2 to 3 cm caudal to the last rib, and one third the distance Figure 1 from the ventral to dorsal midline (Figure 2 A). The incisions are made 3 cm apart, and a flap of transverse abdominalis muscle is elevated (Figure 2 B) A 4 cm by 3 cm seromuscular flap is created in the pyloric antrum (Figure 2 C-D). A branch of the right gastroepiploic artery is incorporated in the flap. One simple interrupted suture can be placed between the stomach wall and the ventral part of the transverse abdominalis muscle flap (Figure 2 E). Using a stay suture, the seromuscular flap is passed through the belt loop in the abdominal

wall (Figure 2 F) The seromuscular flap is sutured back on its original position using 3-0 absorbable monofilament with simple interrupted pattern (Figure 2 E).

POSTOPERATIVE COMPLICATIONS Several complications can occur after surgical treatment of gastric dilatation volvulus. They result from the pathophysiology of the gastric dilatation volvulus syndrome. Shock after surgery results usually from inappropriate treatment prior to surgery, surgical blood loss, anesthetic depression and fluid sequestration due to ileus. Septic shock can result from toxins and bacterial absorption from gastric mucosa necrosis and peritonitis.

Prognostic indicators are gastrectomy with Figure 2 splenectomy, hypotension, DIC, arrhythmias, and peritonitis.

Gastrectomy alone is not a prognostic indicator for survival, however it increases the risk of complications: peritonitis, arrhythmias, and hypotension.

Ventricular arrhythmias are common after gastric dilatation volvulus, especially 36 hours after surgery. It occurs in 50% of the cases. They result from poor myocardial perfusion, ischemia, acidosis, electrolyte imbalance, thromboembolic event, and myocardial depressant factor.

Treatment requires correction of acid-base and electrolyte imbalances, and hydration. Lidocaine, 2 to 4 mg/kg as a slow bolus is given intravenously followed by a constant rate infusion of 50 to 100 microgm/kg/mn is the drug of choice for treatment of ventricular tachycardia. Sotalol will then be administered for 2 weeks. An electrocardiogram will be repeated 2 weeks after surgery to make sure the arrythmias are not present anymore.

Hypokalemia, blood loss, and disseminated intravascular coagulopathy need to be recognized and treated accordingly. Gastric rupture occurs rarely postoperatively but is due to inappropriate assessment of the viability of the stomach at time of surgery. Gastritis secondary to mucosal ischemia is treated with famotidine, and sucralfate.

PERITONITIS Eric Monnet, DVM, PhD, FAHA Diplomate ACVS and ECVS Colorado State University, Fort Collins, Colorado Peritonitis is a life threatening condition in dogs and cats that causes serious metabolic alterations and organ dysfunction Peritonitis is an inflammatory process that involves all, or a portion, of the peritoneal cavity. It results from contamination of the abdominal cavity by either microorganisms or inflammatory chemicals. Peritonitis is characterized by acute abdominal pain.

ETIOLOGY Peritonitis can be caused by the introduction of microorganism into the serosal-lined peritoneal cavity. This may results from traumatic injury, surgical induced lesions, strangulation-necrosis of the gastrointestinal tract, perforation of the bowel, rupture of gastrointestinal ulcers, incarcerated loop of intestine, mesenteric volvulus, or pyometra rupture. Inflammation of the peritoneal cavity may also results from release of neoplastic tissues, blood, urine, or bile into the abdominal cavity. Pancreatitis can trigger peritonitis by local inflammation.

PATHOPHYSIOLOGY Irritation or injury to the peritoneal lining results in direct cellular damage with the release of lysosomal enzymes, kinin and histamine. Cellular damage to capillaries and serous surfaces allows white blood cells, fibrin, fibronectin and fluid to enter the area.

Sympathetic stimulation inhibits peristalsis, which localizes and helps inhibit movement of contaminants through the peritoneal cavity. Omentum moves in the area to increase oxygen tension, deliver white blood cells and absorb bacteria, foreign material or debris.

If the initial response is insufficient to localize the insult, the inflammatory reaction takes place over a larger area and a generalized peritonitis occurs. Bacteria embolize and sepsis is developing. Activation of the arachidonic acid pathway occurs after damage to the cell membrane with production of toxic free radicals, activation of the coagulation cascade. Endotoxins also activate the extrinsic coagulation pathway. Increased amounts of interstitial fluid lead to accumulation of free peritoneal fluid with protein and sodium.

As more peritoneal fluid accumulates there is a decrease in circulating blood volume and hypovolemic shock occurs. Continued accumulation of endotoxin, bacteria, chemicals and white blood cells increases the severity of the inflammatory process. Hemoglobin if present interferes with the chemotactic response of white blood cells, retarding clearance of bacteria. The addition of 4 gm of free hemoglobin/100ml of fluid results in 90% mortality when bacteria are present. Fibrin clots isolates bacteria from the white blood cells. Bacteremia develops with septic shock.

As more fluid accumulates in the abdominal cavity hypotension develops with reduction of the cardiac output. Sympathetic activation results in augmentation of

contractility and vasoconstriction. Pain and increased metabolic rate contributes also to the augmentation of heart rate.

Reduction of kidney perfusion stimulates reninangiotensin system. It results in severe vasoconstriction. After stimulation of aldosterone secretion by renin-angiotensin, water and sodium retention occur which help maintain plasma volume. Augmentation of osmolality stimulates the secretion of anti-diuretic hormone.

Renal vasoconstriction, aldosterone and anti-diuretic hormone release contributes to the reduction of urine production.

Decrease cardiac output and vasoconstriction result in poor tissue perfusion leading to myocardial ischemia, brain damage and renal tubulonecrosis. Electrolyte imbalance plus myocardial ischemia trigger arrhythmia with further reduction of cardiac output.

Bile will produce intense peritoneal irritation. Bacteria might be present if there is an associated cholangiohepatitis. A certain level of endogenous flora is present in the liver and hepatic circulation as a result of normal entero-hepatic circulation. Numerous species have been cultured including Staphylococcus, Streptococcus, E Coli, Klebsiella, Enterobacter, Clostridia, Bacteroides and Fusobacterium. Death will not occur from bile contamination alone. The concentration of bile salts is important in the toxicity of bile peritonitis. Bile salts enhance bacterial proliferation. Bile salts reduce surface tension, bacterial adherence and subsequently neutrophils activity. Bile salts lyse red blood cells, releasing hemoglobin, which enhances bacterial proliferation.

Gastric fluids and pancreatic enzyme are more irritant than bile salts. They cause immediate cellular damage. The acid pH of the gastric fluid prevents bacterial growth initially but if blood is present or foreign material bacterial will develop.

Urine may or may not be contaminated with bacteria. Urine does not create a significant inflammation. Urine peritonitis can cause profound azotemia subsequent to absorption of urine constituents across the peritoneum.

Barium produces an intense chemical peritonitis with hemorrhagic, granulomatous reactions. When combined with bowel perforation, the toxic effect is greater than with either contaminant alone. The morbidity and mortality of peritonitis induced by barium has been correlated to the amount of barium in the peritoneal cavity. Water soluble contrast materials are less toxic but are still associated with a high morbidity if there is concurrent bowel perforation.

Blood causes minimal irritation of the peritoneum and is completely absorbed from the peritoneal cavity within 24 hours. Blood interferes with chemotactic influx of white blood cells. It may impede lymphatic clearance of bacteria.

CLINICAL FINDINGS Local or generalized tenderness may be present in peritonitis. The pain is usually diffuse and the abdomen is tender and tympanic. Splinting of the abdominal wall is common with the slightest touch. Pyrexia, tachycardia, tachypnea and vomiting then develop. Inflammation of the peritoneal cavity causes cessation of normal peristaltic activity and accumulation of fluid and gas.

Marked leukocytosis with a severe left shift is present on the complete blood count. Biochemistry is also helpful to further define the cause of the peritonitis. Platelet counts should be carefully evaluated because lot of dogs with peritonitis will develop DIC. Abdominal paracentesis with cytology is more likely to confirm the diagnosis of peritonitis. Abdominal lavage may help in the diagnosis of a peritonitis if the first abdomocenthesis is negative. In per-acute situations since peritoneal leukocytes counts do not rise until 2-3 hours after contamination the abdominocenthesis may not help in the diagnosis. Peritoneal fluid is an exudate (1,000 to 2,000 white blood cells/microliters, toxic neutrophils) with or without bacteria. An exsudate with a high white blood cell count but without any bacteria is very commonly associated to a perforation of the upper GI. Cytology of the exudate is necessary to evaluate the neutrophils. Aerobic, anaerobic, and fungal culture is required from the exudate. Presence of bile, blood, or urine (creatinine) obtained after tapping the abdomen suggests specific diagnosis. Also dehydrated patients may not have a severe effusion but after rehydration the effusion will get worse. Therefore it is important to constantly evaluate those patients because the diagnosis will change when more fluid is present in the abdomen.

RADIOGRAPHIC EXAMINATION Radiographs may be helpful for the diagnosis of peritonitis. Radiographic examination shows a lack of abdominal contrast and a ground glass appearance. Fluid accumulation and pneumoperitoneum can be seen on radiographs. Pneumoperitoneum is more characteristic of stomach rupture. Free gas in the abdomen may be seen between the liver and the diaphragm; however, this is considered a normal finding for at least 1 week after abdominal surgery. Intraluminal gas pattern may be suggestive of ileus or obstruction. Contrast studies are helpful for assessment of the urinary tract but should otherwise be avoided, particularly if gastrointestinal perforation is suspected or if surgery is inevitable. Ultrasound can be used to evaluate parenchymatous organs and intraabdominal masses.

TREATMENT Treatments of peritonitis have 3 goals: administer appropriate supportive medical treatment (antibiotics, fluid therapy, shock therapy), lavage thoroughly the abdominal cavity with sterile warm saline to flush bacteria or debris, and surgical correction of the primary problem if possible.

Antibiotic therapy is initiated as soon as peritonitis is diagnosed and samples are collected for culture and sensitivity. Usage of intravenous bactericidal drugs that are active against anaerobic and gram negative aerobic organisms is recommended. We are using the combination of Ampicillin (20 mg/kg three times a day) and Enrofloxacin (5 mg/kg 2 times a day). Intraperitoneal administration of antibiotic is contraindicated.

Fluid therapy with crystalloid, colloids should be initiated first with a shock dose since the patients are in hypovolemic shock. Colloids such as Dextran 70, Hetastrach or

plasma are highly recommended for patients with septic shock and endotoxemia.

Hypoglycemia and electrolyte imbalance should be corrected when recognized.

Surgery is necessary to halt ongoing contamination, remove foreign material and adjuvant substances, provide drainage and provide access for enteral nutrition. After correction of primary lesion, animal with generalized peritonitis should undergo lavage of the abdominal cavity with 3 to 4 liters of warm sterile saline. The abdominal cavity is then dried as much as possible.

At the time of closure of the abdominal cavity there are four options for the surgeon: close the abdomen completely, perform a second surgery 24 hours alter to have a second look, place a closed suction drain, or leave the abdomen open with an heavy bandage to contain the abdominal organs. Decision of placing a drain is purely subjective and there is no data in the literature to demonstrate the benefit of draining the abdominal cavity.

Drainage of the abdominal cavity will prevent a compartmental syndrome that can induce anuria. If the contamination was mild and the source of the peritonitis well controlled then the abdomen can be closed. If the peritonitis is mild but has a tendency to be very exudative (bile peritonitis) or the source not well controlled then a drain can be placed. If the contamination of the abdominal cavity is severe or if the source of the contamination is not controlled or if lot of foreign materials are present the abdomen should be left open to drain. Colon trauma, intestinal necrosis after incarceration, strangulation of a loop of bowel, rupture of a pyometra with generalized peritonitis, and necrotico-hemorrhagic pancreatitis are amenable to open abdominal drainage.

Second look surgery: Twenty-four hours after surgery the patient is anesthetized and brought to the operating room. The abdominal cavity is open again. A fluid sample is collected for cytology. A full exploration is performed to evaluate the surgical site and also brake down adhesion to eliminate pockets of fluid. Foreign materials are eliminated mechanically during the exploration. If the surgical site is showing signs of leakage it is then repaired. The abdominal cavity is then flushed aggressively with 3 to 4 liters of warm sterile isotonic solution. A drain can then be placed if needed. The abdomen is then closed. This operation can be repeated 24 hours later if needed.

Surgical technique for placement of drains: Jackson Pratt drained should be placed in the cranial part of the abdominal cavity. The drain should extend between the liver and the diaphragm. The drain then exit in the lateral side of the cavity and connected to a closed suction device that generate between 5 to 10 mm Hg. The drains are maintained for several days until the daily cytology of he abdominal fluid shows significant improvement. The tip of the drain should be cultured at the time of removal. This technique does not allow flushing of the abdominal cavity. The drain allows collection of fluid that can be evaluated daily.

Surgical technique for open abdomen: At the end of the surgical procedure, a loose lace of heavy suture material (#2 monofilament non-absorbable suture) is placed on the edge of the abdominal incision to maintain the abdomen organs inside the abdomen. The two edges of the abdominal incision are not brought close together. Subcutaneous tissue

and skin are not sutured. A layer of 2 or 3 sterile laparotomy sponges is placed on the loose lace. Loops of 2-0 nylon are placed every 2 to 3 cm on the skin 5 to 6 cm away from the edge of the incision and umbilical tap is laced through those loops to maintain the laparotomy sponges. Sterile surgical towels are the applied and maintained in place with an adhesive incises surgical drape. If the patient is a male dog, a urinary catheter is placed and the penis can be incorporated under the adhesive incise surgical drape. Under heavy sedation and analgesia or general anesthesia, bandages are changed every 12 to 24 hours. At each bandage change, the abdomen is flushed with warm sterile saline.

Cytology of the fluid present in the abdominal cavity is performed. When the cytology shows healthy neutrophils and decreased number of bacteria per high power field, the abdomen can be closed. During the open abdomen treatment the patient is kept under appropriated intravenous antibiotherapy. Usually, a combination of ampicillin and enrofloxacin is used until the results from the culture and sensitivity are known. With an open abdomen patients are loosing a great amount of proteins which placed them very quickly in severe hypoproteinemia. Fresh frozen plasma transfusions should then be administered to maintained their preload and oncotic pressures. To limit the severity of the hypoproteinemia a jejunostomy tube is placed at the first surgery to try to supplement the patient in high catabolic stage. Also the plasma transfusions bring coagulation factors that very important for these patients since they are at high risk of disseminated intravenous coagulation (DIC). Since these patients are septic or are at high risk to become septic heart rate, arterial blood pressures, central venous pressure, activated coagulation time, and blood glucose should be monitored closely. Open abdominal drainage is associated with a high morbidity and mortality. In a study, 63% of the patients treated with an open abdomen died in the early postoperative period from complications associated with the open abdomen. The major complications from open abdominal drainage are hypoproteinemia, DIC, and nosocomial infection.

Feeding tube placement: A combination of gastrostomy and jejunostomy tube are used for the management of patients with peritonitis.

Gastrostomy tubes are placed for long term management of the patient and also for decompressing the stomach in the post-operative period. The greater curvature of the body of the stomach is identified. The greater curvature of the body of the stomach is manipulated to identify the are with e least amount of tension after placement against the left abdominal wall behind the last rib. A purse-string suture with 3-0 monofilament absorbable suture is placed in the gastric fundus in the identified area. A Foley catheter (18 to 20 French) is inserted first through the left abdominal wall just behind the last rib.

A stab incision is made in the middle of the purse-string suture and the tip of the Foley introduced in the stomach. The balloon of the Foley catheter is inflated with appropriate amount of saline and the purse-string suture tied.

Four gastropexy sutures (3-0 monofilament absorbable material) are placed between the stomach wall and the abdominal wall. The sutures are evenly distributed around the Foley catheter. A Chinese finger trap suture is placed around the Foley catheter on the skin.

A jejunostomy tube is placed when bypass of the upper part of the gastrointestinal is required. A loop of jejunum is selected distal to the part of the intestine that needs to be bypassed. A purse-string of 3-0 monofilament absorbable suture is placed on the antimesenteric border of the jejunum. The jejunostomy tube (3 to 5 French) is first inserted through the abdominal wall. A stab incision is made in the middle of the pursestring and the jejunostomy tube is introduced in the jejunum 20 cm aborally. The pursestring is tied. Then, 4 jejunopexy sutures are placed evenly around the jejunostomy tube between the abdominal wall and the jejunum.

Feeding can be started immediately after placement of the jejunostomy tube. A liquid diet is administered continuously through a feeding pump. The catheter needs to be flushed every 4 hours to prevent its obstruction. The tube needs to stay in place for at least 4 days before its removal to allow appropriate sealing of the pexy. Usually, the jejunostomy tube is for short-term usage because a pump is required to deliver the diet.

Jejunostomy tube is advantageous for patients requiring multiple anesthesia (open abdominal drainage) or being profusely vomiting before surgery.

Prognosis is worse for young and very old animals, or in the presence of delayed diagnosis, greater or more virulent contamination or poor nutrition. Mortality rate is high if organ failure is present. Poor prognosis is associated with refractory hypotension, cardiovascular collapse and development of DIC. Mortality could be as high as 68% for peritonitis. Mortality rate with open abdomen has been reported as high as 48%. 

SURGERY OF THE LIVER AND GALL BLADDER Eric Monnet, DVM, PhD, FAHA Diplomate ACVS and ECVS Colorado State University, Fort Collins, Colorado Surgery of the liver and gall bladder is indicated for liver trauma, liver neoplasia, liver abscess, liver torsion, bile duct obstruction, and gallbladder mucocele. Liver and spleen are the two most common organs to induce a hemodabdomen after trauma. It rarely requires surgery unless the patient cannot be stabilized with appropriate fluid-therapy and blood transfusion. Liver trauma is treated surgically by compression, tamponnade with the omentum or liver lobectomy. Liver neoplasia is rare in dogs. Liver adenocarcinoma and lymphoma are the most common tumors found in dogs. Massive adenocarcinoma are well amenable to surgical treatment since they are slow growing and metastasize slowly.

Liver abscess are rare in dogs and cats and usually their cause is not well known. Gramnegative aerobic bacteria are the most commonly found in the liver abscess. Liver lobe torsion usually involves the left liver lobes. Cholelithiasis has to be considered when obstructive icterus is present Stones could be solitary, numerous or sandlike. Most canine and feline stones are calcium salts of bilirubinate. Bile stasis and inflammation might be cause for the formation of bile stones. Cholecystitis has been reported in dogs. It could be acute or chronic and a necrotizing or emphysematous form has been described.

Extrahepatic biliary obstruction occurs when disease processes interfere with normal flow of bile from the liver and the gallbladder into the intestine.

General considerations Regenerative capacity Removal of 70% of the liver is tolerated. The general condition of the patient conditions how much liver can be removed safely. If more is resected it will result in portal hypertension because there is not enough liver parenchyma left to access the entire blood flow from the portal vein. Regeneration of the liver starts with 24 hours of the surgery and peaks at 3 days. There is hyperplasia and compensatory hypertrophy of the remaining hepatocytes. The liver mass can be restored within six weeks after 70% hepatectomy.

Metabolic alterations Coagulation is evaluated in any patients with hepatobiliary disease. In one study, prothrombine time was elevated in 66% of the animal with liver disease. Plasma fibrinogen remain normal until almost liver function is lost Vitamin K deficiency resulting in coagulopathy may occur with prolonged complete bile duct obstruction. Vitamin K administration (1 to 2 mg/kg subcutaneously) is

sufficient to increase their level in 3 to 12 hours. Fresh frozen plasma is administered if the coagulation times are still prolonged.

Hypoglycemia can occurs with 48 hours of partial liver lobectomy but does not always happened after major hepatectomy. Intravenous infusion f glucose (10%) would then be required. Albumin concentration is reduced after massive liver lobectomy because of the low level of production. Bilirubin can increase but usually goes back to normal within one week. Increased liver enzymes will occur after major resection and will persist for 4 to 6 weeks.

Antibiotherapy Portal venous blood is an important source of bacteria for the liver. Infections of the liver and biliary tract commonly involve Gram-negative aerobic bacteria (E coli, Enterococcis faecalis, Proteus, Klebsiella). Anaerobic bacteria can also colonize the liver in dogs (Clostridium).

Antibiotics are routinely administered when hepatobiliary surgery is performed.

Cephalosporins provide broad spectrum coverage.

When anaerobic bacteria are suspected metronidazole or enrofloxacine should be used.

Anatomy The liver has 6 lobes: left medial and lateral, right medial and lateral, quadrate lobe and the caudate lobe with two processes. The liver lobes are attached to the diaphragm by the triangular ligaments. There are also the hepato-gastric ligament, duodeno-hepatic ligament with the bile duct and hepato-renal ligament stabilizing the liver. The liver receives 70 % of its blood supply from the portal vein and 30 % from the hepatic artery.

The blood from the hepatic artery and the portal vein mixes in the hepatic sinusoids and is released in the caudal vena cava through the hepatic vein. There is on hepatic vein per liver lobe.

Surgical techniques Liver Surgical biopsy Liver biopsies are commonly taken during abdominal exploration. The guillotine technique with a 3-0 braided suture is commonly used to remove a small fragment of the liver. Forceps can be used to make small indentation in the edges of the liver lobes.

Several biopsy can be taken from different liver lobes. Biopsy can be submitted also for cultures. If the edges of the biopsy are bleeding, cautery can be used to control the bleeding or gelfoam can be applied.

Partial liver lobectomy Partial liver lobectomy can be performed to remove the distal end of a liver lobe with a small lesion. Occlusion of the blood flow to the liver can be accomplish by compressing the hepatic artery and the portal vein with a vascular clamp or a Bulldog clamp.

After the line of resection has been decided, mattress sutures with 2-0 monofilament absorbable suture material are placed across the liver parenchyma and tighten to crush the tissue. This technique allows crushing of the parenchyma and ligation of the major vessels. Several mattress sutures are placed across the section of the liver lobes.

Mattress sutures should be 2 to 3 cm long. After all the sutures have been placed the blood vessels are cut with a scissors. Stapling equipment can laso be used to performed a partial liver lobectomy. Usually the section the liver lobs is bleeding significantly with this technique. Cautery can be used to cauterize the small vessels that are still bleeding.

Alos Gelfoam can be applied to the liver or omentum can be patched to the liver to tamponnade the section of the liver.

Liver lobectomy Liver lobectomy requires ligation of the blood vessels and hepatic duct at the hilus of the liver. Each liver lobe can be removed separately. Right liver lobes and caudate lobes are the most difficult lobes to remove because of their close proximity to the vena cava.

The dissection starts from caudally with exposure of the branch of the portal. IT is dissected and double ligated. Then hepatic artery and the hepatic duct draining the liver lobes are dissected and ligated next. Finally, the hepatic vein is identified after finger fragmentation of the liver parenchyma at the base of the liver lobe. Finger fragmentation reduces the amount of bleeding from the liver parenchyma and prevents laceration of major blood vessels. After the hepatic vein has been exposed it is double ligated and divided. The hepatic vein of the right caudal liver lobes is better clamped with a vascular clamp divided and then sawn as an open vessel. This technique avoid kinking of the vena cava or slippage of the suture of the stub of the hepatic vein. If the quadrate lobe has to be removed the gall bladder is dissected away from the liver parenchyma. At the end of the procedure either the gall bladder is removed or pexied to another liver lobes to prevent torsion and obstruction of the cystic duct.

Stapling equipment (TA 30 V3 or TA55) can be used to perform a liver lobectomy of the left liver lobes.

Gallbladder and bile duct Cholecystotomy Cholecystotomy is indicated to removed inspissated bile or biliary sludge, gelatinous bile or gallstones and bile duct stones. It is also performed to cannulate the bile duct to evaluate its patency.

Two stay suture of 3-0 monofilamet are placed on the gall bladder. A small incision is made between the two stay sutures and suction is used to aspirate the bile overflow before it contaminates the abdominal cavity. The incision is then enlarged with Metzembaum scissors. The incision should be long enough to perform the procedure.

The bile duct needs to be catheterized before closure. It could be difficult to achieve a good catheterization because of the angle of the cystic duct with the common bile duct.

A biopsy of he wall of the gallbladder is taken for histology and culture before closure.

The gallbladder is then closed with a simple suture pattern with 4-0 monofilament absorbable suture. A one-layer closure is sufficient.

Cholecystectomy A cholecystectomy is required when the gallbladder is the primary cause of the pathological process or if the damages to the gall bladder are too severe and might contribute to the recurrence of the disease. Cholecystitis and gallbladder mucocele are best treated by cholecystectomy.

Cholecystectomy requires the dissection of the gallbladder form the quadrate lobe. The gallbladder is lodged in the hepatic fossa and it is covered by visceral peritoneum. The dissection starts at the fundus of the gall bladder by an incision through the visceral peritoneum. The dissection should not be in the liver parenchyma because severe bleeding will occur. The dissection is then carried with cautery toward the infudibulum of the gall bladder. The cystic duct and the cystic artery are isolated, clamped, and ligated. The cystic duct is ligated at a sufficient distance from the common bile duct to prevent kinking of the common bile duct. If the liver parenchyma is bleeding, cautery could be used to control the bleeding or gentle pressure could be applied for 5 minutes.

Gelfoam could also be applied on the bleeding surface of the liver.

Cholecystectomy can also be performed with laparoscopy. Only cases without occlusion of the common bile duct can be operated with minimally invasive surgery.

Usually the cystic duct is dissected first and ligated with clips. After successful ligation of the cystic duct the gall bladder is dissected from the hepatic fossa of the quadrate lobe.

If the gall bladder is too large the dissection can be started at the level of the apex. IT is then important to establish a good plane of dissection between the gall bladder and the liver parenchyma. The cystic is then ligated last.

Cholecystoduodenostomy Cholecystoduodenostomy is the procedure of choice for bile diversion in dogs and cats when the gall bladder is not directly involved in the disease process that is causing the bile duct obstruction. It could be a palliative procedure for bile duct obstruction due to neoplasia.

The gall bladder is detached for the hepatic fossa as described for the cholecystectomy.

Then the gall bladder is brought in contact with the duodenum with two stay sutures.

Special attention should be placed on the cystic duct to avoid twisting and occlusion. The

stoma between the gall bladder and the duodenum should be between 2 and 4 cm. A first layer of suture is applied between serosal layers on the back side of the duodenum. The gall bladder and the duodenum are then incised. A simple continuous suture is placed between the muscosa layers of the gall bladder and the duodenum. Finally, another layer of simple continuous suture is placed between the serosa of the duodenum and the serosa of the gall bladder. 4-0 monofilament absorbable suture material is used for the procedure.

After cholecystoduodenostomy, the patients are at risk for ascending cholangiohepatitis and needs to be maintained on enrofloxacin for long term.

Choledochoduodenostomy Choledochoduodenostomy can be performed if a benign obstruction occurs at the distal end of the bile duct. Significant dilation of he proximal art of the common bile has to be present to be able to perform this procedure.

The distal part of the common bile duct is separated form the pancreas and the duodenum. It is then implanted more proximal into the wall of the duodenum with two simple interrupted sutures.

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SURGERY FOR URINARY STONES
 LOWER URINARY TRACT Eric Monnet, DVM, PhD, FAHA Diplomate ACVS and ECVS Colorado State University, Fort Collins, Colorado The most common cause of urinary obstruction in small animal surgery is urinary stones in the urethra. Other causes of obstruction are neoplasia in the urethra, and neoplasia compressing the urethra. Generally, small cystic calculi migrate to the neck of the bladder during micturition and pass into the urethra. In the male, urethral calculi most commonly lodge caudal to the os penis. In the female, calculi may lodge at any location along the length of the urethra. Urethral obstruction is more common in the male than female.

Urinary obstruction requires medical treatment to stabilize the patient to surgery and surgical treatment to release the obstruction. Dogs and cats with urinary obstruction are presented with hematuria, stranguria, and pollakiuria. Plain radiographs or radiographs with contrast material (excretory radiographs, cystourethrograms) will confirm the presence of a urinary stones in the urethra.

MEDICAL MANAGEMENT Blood work with complete blood count, and biochemistry is required to evaluate kidney function of the patient. Urinary obstruction is associated with severe post renal azotemia and severe electrolytes imbalance.

Hyperkalemia is the most common electrolyte abnormality. Hyperkalemia can induce severe bradycardia if the concentration is over 5 me/dl. Therefore it is important to reduce the hyperkalemia before anesthetizing patients with urinary obstruction.

The most efficient technique to lower the potassium concentration is to diaries the patient. If the patient can still urinate on its own intravenous fluid therapy will induce a diuresis. If the patient cannot urinate cystocenthesis can be performed to empty the bladder. The concentration of potassium is monitored very closely to be able to anesthetize the patient as soon as the potassium is back to normal limits. If diuresis is not efficient insuline/glucose and bicarbonate can be used. While the glusoce moves intracellular it brings the potassium in the intracellular space. Potassium and hydrogen particles are exchanged which results in metabolic acidemia. Therefore bicarbonate is required to control the acidosis. This technique lowers the potassium within 30 minutes.

If the potassium concentration is not reduced then calcium gluconate is used to protect the myocardium form the effect of potassium.

SURGICAL MANAGEMENT When the potassium concentration is within normal limits general anesthesia can be performed. After induction of general anesthesia the urinary stones lodged in the urethra

can be retropulsed in the bladder. All the efforts should be made to retroflux the uroliths in the bladder. It is easier to performed a cystotomy than an urethrotomy, and there is less morbidity associated.

Retropulsion To perform a successful repulsion the following steps have to be performed after inducing deep general anesthesia with intubation a) Thoroughly mix 45 cc of sterile saline and 15 cc of Surgilube in a 60 cc syringe and attach to the largest high density polyethylene urinary catheter that will pass through the os penis (5 to 8 French). b) Pass the catheter up to and against the calculus. If the patient is a male place a gauze sponge around the tip of the penis and occlude the penis around the catheter by squeezing it with thumb and finger. c) Using a back and forth action on the catheter, simultaneously inject the saline/ lubricant mix under pressure. The calculi and urethra are lubricated and the viscosity of the mix encourages the calculus to dislodge and flush into the bladder. This technique is attempted regardless of how many stones are in the urethra. d) If the above technique fails, place a finger in the rectum, palpate the urethra, and occlude its lumen, repeat step C above and when maximum pressure is exerted on the urethra by the saline/lubricant mix, suddenly release digital urethral occlusion allowing lodged calculi to flush into the bladder. This technique allows maximal dilatation of the urethra.

This technique is successful in most of the cases. Lidocaine can also be injected while the catheter is in contact with the stone to release a spasm of the urethra around the stones.

If the stones are successfully retroflux in the bladder, the urinary catheter is left in place to prevent migration of the stones back into the urethra.

If the stone cannot be retroflux in the bladder then a urethrotomy is performed.

Cystotomy After a midline incision in the caudal abdomen, a ventral cystotomy is performed to expose the inside of the bladder. After placing three or four stay sutures in the wall of the bladder to minimize trauma during manipulation of the bladder, the uroliths are removed either with a spoon, or suction. The bladder neck and lumen should be explored with a finger to detect remaining large uroliths. A biopsy of bladder wall should be performed then for culture and sensitivity.

Bladder wall culture gives more reliable results regarding bacterial infection than urine culture. Bladder neck is flushed with warm sterile saline to remove small uroliths. The urethra is flushed with the catheter placed to retroflushed the stones in the bladder. While sterile saline is flushed profusely in the urethra the catheter is removed. With this technique little uroliths left in the urethra are

flushed in the bladder. Then a catheter is introduced in the proximal urethra and large amounts of saline are used to flush the urethra normograde. Before closing the bladder a catheter is introduced from the bladder in the urethra to confirm patency of the urethra. It is not necessary to maintain a urinary catheter postoperatively.

It is recommended to take a post-operative radiographs to make sure all the stones have been removed.

Urethrotomy A urethrotomy (an incision over the calculi) may be performed to remove calculi that cannot be retropulsed. It is usually performed in the prescrotal or perineal region. With a urinary catheter in place to the obstruction a 5 cm midline incision is made over the uroliths. The subcutaneous tissue is dissected and the retractor penis muscle is retracted on one side. The urethral is dorsal to the retractor penile muscle. A 15 scalpel blade is use to longitudinally incise the urethra over the uroliths. The uroliths are removed and the catheter advanced. If other uroliths are present they can either be retrieved through the urethrotomy or they can be flushed back in the bladder. Then a cystotomy is required.

The urethrotomy incision can be left open or suture with an absorbable suture in a continuous pattern on the urethra . Subcutaneous tissue and skin are closed. If the incision is left open it is going to granulate and closed by second intention. Urine is leaking through the incision for several days. The corpus spongiosum will bleed when the dog urinates or becomes excited.

Urethrostomy A urethrosotmy (a permanent opening to allow calculi to pass) may be indicated in animals that are chronic recurrent calculi formers (e.g., urate calculi in Dalmatians).

Scrotal urethrostomy Scrotal urethrostomy is the technique of choice in male dogs because the urethra has its largest diameter at the level of the scrotum. The dog is placed in dorsal recumbency and a urethral catheter is placed. After castration and scrotal ablation, the retractor penile muscle is retracted on the side to expose the ventral aspect of the urethra. The urethra is incised longitudinally over 3-4 cm. The periurethral tissue is sutured to the subcutaneous tissue with a 4-0 absorbable suture in a simple interrupted pattern. The urethral mucosa is then sutured to the skin with 4-0 non-absorbable monofilament in a simple continuous pattern. The urethra is more superficial in the scrotal area, surrounded by less cavernous tissue. Complications of an urethrostomy are hemorrhage, stricture, and dermatitis from urine scalding. Hemorrhage happens for 6 to 7 days after surgery when the dog urinates or becomes excited. Sedation might be required for a week to 10 days after surgery to help control bleeding. Stricture mostly occurs is the dogs is self-traumatizing the surgical site. An E collar is recommended for 10 days. After a urethrostomy dogs are at more risk of ascending UTI because the urethra is shorter.

Perineal urethrostomy

In cats a perineal urethrostomy is performed. The cat is positioned in ventral recumbency at the end of the table. An elliptical incision is performed around the prepuce and the scrotum.

The cat is castrated. The penis is isolated and the ischiocavernosus muscles are exposed by blunt dissection and transected to their attachment to the ischium. After care blunt dissection ventrally posterior displacement of the penis is possible. The retractor penile muscle is transected near the external anal sphincter muscle. The penile urethral is incised dorsal to the bulbourethral glands. At this point the urethra is wide (4 mm). The pelvic urethra and 3 cm of the penile urethra are sutured to the skin with 4-0 monofilament in a simple interrupted pattern. The remaining of the penile urethra and penis are amputated. An Elizabethan collar is used to prevent self-mutilation. Complications are hemorrhage, cystitis, urethral stricture, selfmutilation, and wound dehiscence.

PATIENT MONITORING Post operatively patient needs to be monitored for signs of uroabdomen. Animals presenting with complete urinary obstruction and postrenal azotemia are continued on crystalloid IV therapy until serum urea nitrogen and creatinine return to normal. Postobstruction diuresis happened after the obstruction has been released. Fluid rate should be increased to maintain the hydration status of the patient. Treatment for UTI and dietary management are required to prevent reoccurence. After a cystotomy hematuria is possible for 2 - 3 days postoperatively. After a urethrotomy or a urethrostomy, hemorrhage from the urethral stoma is common in the immediate postsurgical period. It generally occurs 4 - 5 days postoperatively, but occasionally will last up to 2 weeks.

Apply an Elizabethan collar to prevent self-mutilation.

SURGERY OF THE PANCREAS Eric Monnet, DVM, PhD, FAHA Diplomate ACVS and ECVS Colorado State University, Fort Collins, Colorado Pancreatic surgery is indicated for lesions of the pancreas such as neoplasms, abscesses, and pseudocysts. Surgery is usually not indicated for acute pancreatic unless there is indication of abscess formation and severe peritonitis, or obstruction of the duodenum and the bile duct. In some cases, the presence of pancreatic pathology may not be obvious until the surgeon is in the midst of an abdominal exploration. Therefore it is important for the surgeon to have some general knowledge on pancreatic surgery and to be prepared to perform pancreatic surgery when needed.

ANATOMY The pancreas develops from the first part of the duodenum to which it retains a close association. The pancreas has a V shape with an angle located against the cranial part of the duodenum. The largest segment is located along the duodenum and it is called the right limb of the pancreas. It shares it blood supply with the duodenum through the pancreatico-duodenal artery and it lies in the mesoduodenum. The smaller and thicker segment of the pancreas or left limb of the pancreas lies in the deep leaf of the greater omentum and extend obliquely caudally, dorsally and to the left. It is not intimately associated to any other organ in the abdomen. The left limb of the pancreas receives its blood supply form the splenic artery and the hepatic artery. The left and right limbs of the pancreas meet at the apex of a V (body of the pancreas).

The exocrine portion of the pancreas drains through the pancreatic duct. It is totally concealed in the parenchyma of the pancreas. It extends longitudinally in the middle of the gland and terminates in the duodenum with a straight angle. Usually there are two ducts present in dog and cat. The anatomy of the ducts is highly variable and most of the time they communicate with each other within the parenchyma. The ducts enter the duodenum usually 3 to 4 cm apart. The pancreatic duct ( of Wirsung) usually opens with the bile duct in the major duodenal papilla situated 4 to 5 cm distal to the pylorus. It is the principal and usually the only duct for cats. It is usually small for dogs and drained only the left lobe of the pancreas. The accessory pancreatic duct (of Santorini) is the major duct for dogs and it is present in only 20 % of the cats. It opens in the minor duodenal papilla 2 cm distal to the major papilla.

SURGICAL PROCEDURES Principles of pancreatic surgery Access to the pancreas is gained by a midline laparotomy from the xyphoid to the pubis. Balfour retractors are used to provide adequate exposure of the abdominal cavity.

First a complete abdominal exploration should be performed. The free border of the

greater omentum is brought forward out of the abdominal cavity and wrapped in moist towels. The duodenum is brought into view to visualize the right limb of the pancreas.

The colon is moved caudally to expose the tip of the right limb. The left limb of the pancreas is seen within the deep leaf of the greater omentum after a cranial retraction of the stomach. The body of the pancreas is visualized at the junction of the pylorus and the duodenum.

The pancreas should be manipulated gently during the surgery. However the risk of inducing a pancreatitis with surgical manipulation is very limited even if a biopsy is taken.

Pancreatic biopsy Pancreatic biopsy can be harvested with a shaving technique. A # 15 blade is used to shave a small part of a pancreatic lobule. This technique only allows small biopsies specimens.

The guillotine technique with a loop of absorbable suture can be used to take a bigger specimen. Placement of a suture avoid leakage of pancreatic enzyme or bleeding if the pancreatic duct or a vessel are damaged during the biopsy. Usually several lobules can be isolated with sharp dissection and the loop of suture placed at their base.

Pancreatic biopsy can also be collected with laparoscopy and special biopsy forceps.

This technique is very efficient and only require sedation.

Partial pancreatectomy Partial pancreatectomy can be performed with a suture fracture technique or with a dissection-ligation technique of the pancreatic parenchyma down to the ducts and ligature. Both techniques are acceptable and do not induce severe pancreatitis in dogs and cats. Partial pancreatectomy involving the central part of the pancreas are more difficult because the surgeon should pay attention not to ligate the common duct.

In both procedures the part of pancreas that will be removed needs to be isolated. The mesoduodenum or the deep leaf of the greater omentum are dissected away for the pancreas. Partial pancreatectomy of the right limb of the pancreas requires careful blunt separation of the pancreas from the duodenum without inducing a trauma to the pancreatico-duodenal artery. During partial pancreatectomy of the left limb of the pancreas it is important to preserve the splenic artery.

In the suture fracture technique, an incision is made in the omentum or the mesoduodenum on each side of the tissue to be removed. A non-absorbable suture is passed around the pancreas proximal to the area to resect. The suture is then tied to crush through the parenchyma. Blood vessels will be ligated as well as the duct. The specimen distal to the ligature can be excised, leaving a small amount of tissue caudal to the suture.

In the dissection ligation technique the lobules are separated with blunt and sharp dissection. The dissection is completed when the ducts and the blood vessels are

exposed. These structures are then ligated with a non-absorbable suture. The tissue distal to the ligature can then be resected leaving some tissue distal to the suture.

Extensive partial pancreatectomy can be performed without impairing endocrine or exocrine function. No metabolic abnormalities have been reported after resection of 80% of the pancreas if the pancreatic duct has been left intact.

Complete pancreatectomy Complete pancreatectomy is indicated for neoplasia involving most of the pancreas, severe necrotico-hemorrhagic pancreatitis not improving with appropriate medical treatment. This procedure is extremely rarely performed. Patients are then diabetic and pancreatic insufficient.

POSTOPERATIVE CARE Lavage and drainage of pancreatic surgery are important is sepsis and necrotic tissue are present to eliminate inflammatory cells and mediators. Antibiotics are maintained as long as needed if peritonitis is present. Intravenous fluids are maintained to prevent dehydration and treat electrolytes imbalance. Feeding with a jejunostomy tube is started immediately after surgery until the patient can eat on its own without vomiting. If a complete pancreatectomy has been performed exocrine pancreatic supplementation is required. Also endocrine deficiency will be treated with insulin.

SPECIAL CONSIDERATIONS Pancreatitis Acute and chronic pancreatitis are common pathology in dogs and cats. Several factors have been associated with the conditions; high fat diet, hyperlipidemia, hypercalcemia, drugs, infection, trauma, and ischemia. Pancreatitis is due to an early activation and release of proteolytic and lipolytic enzymes, which causes an autodigestion of the pancreas.

The activation factor for a pancreatitis is the transformation of the trypsinogenin trypsin within the pancreatic parenchyma. Other enzymes will then be activated leading to the destruction of the fibrous tissue, interstitial tissue, elastic tissue in the arteries. It results in an edematous hemorrhagic process with thrombosis of the blood vessels. The release of different proteolytic enzymes, inflammatory mediator results in a multisystemic effect that can lead to a septic shock and a multiorgan failure.

Phospholipase activation can reduce the amount in surfactant in lungs and induces a severe pulmonary edema. A phlegmon is the result of an acute pancreatitis and it is a solid mass of indurated pancreatic tissue and surrounding tissue. It is the result of edema, inflammation and necrosis.

The treatment of pancreatitis is not clearly established. Medical treatment with fluid therapy, antibiotic and antiemetic therapy is tried first. Transfusion with plasma is recommended to maintain the oncotic pressure and provide macroglobulin. The role of surgery for an acute pancreatitis has not been established. However, the abdominal exploration with abdominal lavage, biopsy, and placement of a jejunostomy tube is

indicated. The placement of jejunosotmy tube is paramount to allow delivery of calories and proteins to a patient in a high catabolic state without activating the pancreas. Chronic pancreatitis is usually associated with an obstruction of the bile duct. It is then necessary to release the obstruction by performing a choledocostomy or a cholecystoduodenostomy.

Pancreatic abscess Pancreatic abscess is a serious complication of an acute or chronic pancreatitis. It results from a hematogenous or retrograde contamination of a pancreatic phelgmon. An abscess is visible on ultrasound. At the time of surgery, it appears as a pancreatic and peripancreatic collection of hemorrhagic, necrotic and purulent tissue. Pancreatic abscess is associated with an extremely poor prognosis.

Surgery is indicated to debride the abscess.

If the debridement with partial pancreatectomy is not possible, marsupialization in the stomach has been described for the abscess of the left limb of the pancreas. Abdominal drainage is recommended to improve survival after surgery. It will provide continuous drainage of the abdominal cavity and daily flushing will be required. Closed suction drains can be used instead of open abdominal drainage. During surgery a gastro-jejunostomy tube is placed to aspirate the stomach and feed the patient in the jejunum.

In the postoperative period, animals with pancreatic abscess need to be watched for sepsis, disseminated intravascular coagulation, hyporproteinemia, hypotension, and renal failure.

Pancreatic pseudocyst Pancreatic pseudocyst is an accumulation of pancreatic fluid within the pancreatic parenchyma. It is usually surrounded by granulation tissue. It is associated with chronic pancreatitis. Pseudocysts have the tendency to resolve in their own in 2 to 3 weeks.

Pseudocyst can hemorrhage, become infected and produce and abscess or rupture.

Pseudocysts that are not resorbing need to be removed surgically.

A partial pancreatectomy is indicated to remove a pseudocyst if it is located in the distal part of the right or left pancreas. If a partial pancreatectomy is not possible then the pseudocyst needs to be drained and omentalized.

Pancreatic neoplasia Insulinoma Insulinoma is a tumor of the beta cells. It is most commonly seen in older dogs. It results in hypoglycemia, weakness, seizures, muscle tremors,exercise intolerance, and lethargy. Diagnosis is based on hypoglycemia with a high level of insulin. Exploratory celiotomy is indicated even if it is not a cure because of functional metastasis. It usually allows a better control of the clinical signs.

Insulinoma could be either a single or multiple discrete masses or diffuse. Careful palpation of the entire pancreas is important because the insulinoma might be extremely

small. Insulinoma is firm on palpation and it can occur in any part of the pancreas.

Methylene blue has been used to stain pancreatic tissue. A dose of 3 mg/kg intravenously has been recommended 30 min prior to surgery. However, hemolytic anemia can result from the methylene blue injection.

Wide excision of the pancreas is recommended because insulinomas are not encapsulated. Metastasis is common with insulinoma. They are located in lymph nodes and liver. Metastasis need to be removed if possible because they are functional.

Postoperatively, the blood glucose is monitored every 4 to 6 hours. The blood glucose will increase shortly after surgery and hyperglycemia is not unusual because the other beta cells are atrophied. Insulin may then be required for one to two weeks.

Pancreatic exocrine carcinoma Pancreatic exocrine carcinoma is not a common tumor that is usually diagnosed late in the progression of the disease. Animals are anorexic, weak and they are presented for weight loss and vomiting. Icterus due to obstruction of bile duct is usually present.

Ultrasound diagnoses a pancreatic mass. At the time of surgery, the tumor is so invasive that resection is impossible.

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LARYNGEAL PARALYSIS Eric Monnet, DVM, PhD, FAHA Diplomate ACVS and ECVS Colorado State University, Fort Collins, Colorado The laryngeal functions are to regulate airflow, voice production, and prevent inhalation of food. If the intrinsic muscles and/or the nerve supply of the larynx are not normal laryngeal functions are compromised.

The dorsal cricoarytenoide muscle abducts the arytenoid cartilages at each inspiration.

The laryngeal recurrent nerve innervates this muscle. Central lesions or lesions to the laryngeal recurrent nerve or to the dorsal cricoarytenoide muscle result in laryngeal paralysis in dogs and cats. Laryngeal paralysis can be unilateral or bilateral ETIOLOGY Congenital and acquired forms of laryngeal paralysis have been recognized in dogs and cats.

Congenital Laryngeal Paralysis Congenital laryngeal paralysis has been reported in Bouvier des Flandres, bull terrier, Dalmatian, Rottweiller and Huskies. Bouvier des Flandres and bull terrier have mostly been reported from Europe while the Dalmatian and Huskies from United States.

Laryngeal paralysis has a hereditary transmission in Bouvier des Flandres with an autosomal dominant trait. Dogs with congenital laryngeal paralysis are clinical at an early age (before one year old) than dogs with acquired laryngeal paralysis. Usually dogs with congenital laryngeal paralysis have several neurological deficits like ataxia.

Acquired Laryngeal Paralysis Acquired laryngeal paralysis is most commonly reported in Labrador retriever, Golden retriever, St Bernard and Irish Setter at an age of 9 years old. It has been reported in cats.

Acquired laryngeal paralysis is more frequently idiopathic; however, other causes should be ruled out. Several diseases and conditions may contribute to laryngeal paralysis. A cranial mediastinal or neck mass stretching or compressing the laryngeal recurrent nerves can induce a laryngeal paralysis. Trauma to the laryngeal recurrent nerve during dogfights or during surgery in the neck can cause of laryngeal paralysis. Laryngeal paralysis in the cat has been diagnosed after bilateral thyroidectomy. Finally, a ployneuropathy involving the laryngeal recurrent nerve is the most common cause of laryngeal paralysis. The polyneuropathy can be due to an endocrine insufficiency (hypthyroidism) . However most of the time a diagnosis of idiopathic polyneuropathy is made because no causes can be identified. A myopathy involving the intrinsic muscle of the larynx.

CLINICAL FINDINGS History The presenting signs are similar for the congenital and acquired forms. Progression of signs is often slow; months to years may pass before an animal develops severe respiratory distress. Early signs include change in voice, followed by gagging and coughing, especially during eating or drinking. Endurance decreases and laryngeal stridor (especially inspiratory) increases as the airway occlusion worsens. Episodes of severe difficulty breathing, cyanosis, or syncope occur in severely affected patients. Male dogs are approximately three times more affected than female. Laryngeal paralysis can be accompanied with various degrees of dysphagia, which significantly enhances the probability of aspiration pneumonia after surgical correction of the laryngeal paralysis.

Physical Examination The physical examination of dogs with laryngeal paralysis is fairly unremarkable. Dogs have a difficulty breathing on inspiration that is not alleviated with open mouth breathing.

Mild lateral compression of the larynx significantly increases inspiratory effort. Referred upper airway sounds are present during auscultation of the thoracic cavity. Auscultation of the thoracic cavity and the lung field may reveal the presence of pneumonia in the cranial lung lobe due to aspiration. Palpation of the muscle mass may reveal skeletal muscle atrophy in cases of polyneuropathy. The tibial cranial muscle is very commonly atrophied in dogs with endocrine polyneuropathy. A complete neurological examination is required to evaluate the animal for a polyneuropathy.

Laboratory Findings Complete blood count and chemistry profile are usually within normal limits.

Hypercholesterolemia, hyperlipidemia, and augmentation of liver enzymes activity are present on the chemistry profile for dogs with hypothyroidism. A thyroid profile with endogenous TSH and free T4 is then required to further define the diagnosis. Laryngeal paralysis has inconsistent correlation with hypothyroidism.

Radiographic Examination It is necessary to perform a radiographic examination of the thoracic cavity for the evaluation of the lung parenchyma and the esophagus. Aspiration pneumonia is common finding pre-operatively in dogs with laryngeal paralysis. If aspiration pneumonia is present the surgical intervention should be delayed until the aspiration pneumonia resolved. Pulmonary edema is not uncommon in dogs with an acute exacerbation of their clinical signs. Pulmonary edema needs to be treated aggressively and the surgery for the laryngeal paralysis does not need to be delayed. Megaesophagus might be present in dogs with laryngeal paralysis especially if the paralysis is due to polyneuropathy or polymyopathy. Megaesophagus places the animal at more risk for aspiration pneumonia after surgery. Radiographic examination of the larynx is unremarkable.

Laryngeal Examination A laryngeal examination under general anesthesia is required for the diagnosis of laryngeal paralysis. A light plane of anesthesia is required to be able to evaluate the laryngeal function during each inspiration. Thiopental or propofol is used intravenously as needed for the anesthesia. The animal should be anesthetized to the point at which the mouth can be opened easily and a laryngeal reflex is still present. If the animal is too deeply anesthetized the larynx looks paralyzed even in the normal animal. If the plane is too deep it is important to let the animal approach consciousness and examine the laryngeal function during this time. During the laryngeal examination, motion of the arytenoid cartilage is observed during inspiration. Dopram intravenously can be used to stimulate the central respiratory center and have a better laryngeal examination. The animal should be placed in sternal recumbency and the head elevated to the level that it is normally carried. In the normal animal the vocal fold and the arytenoids should abduct during inspiration and passively relax during expiration. The arytenoid cartilages and the vocal cords are immobile and drawn toward midline during inspiration if the animal has laryngeal paralysis. If the paralysis is unilateral only one cartilage is not moving. Edema and erythema of the mucosa of the arytenoid cartilages is present on the dorsal part of the larynx and appear to be due to repeat trauma of the arytenoid touching each other at each inspiration. Paradoxical motion of the arytenoid can be present and makes the diagnosis more difficult. With paradoxical motion the arytenoid cartilages are sucked in the airway during inspiration and are moving back to a normal position during expiration. This gives the impression the patient does not have laryngeal paralysis.

TREATMENT Medical treatment is reserved for the emergency treatment while the surgical treatment is for the long term treatment of the condition. Surgery will improve the quality of life of the patient Medical Treatment: Emergency Treatment Animals are usually presented with acute cyanosis or collapse as a result of upper airway obstruction. Most animals in a cyanotic crisis precipitated by upper airway obstruction recover initially with medical therapy. Excitement or increase in the ambient temperature can trigger an acute onset of inspiratory dyspnea. Excitement or increase in the ambient temperature increases the respiratory rate, which results in trauma to the mucosa of the arytenoid cartilage. Inflammation and acute swelling of the mucosa of the arytenoid cartilages can exacerbate the chronic airway obstruction and induce an acute onset of inspiratory dyspnea. A vicious circle is then initiated.

Corticosteroids are given intravenously (dexamethasone, 0.2 to 1.0 mg/kg BID) to reduce laryngeal inflammation and edema. At the same time, oxygen is administered by mask or oxygen cage to alleviate hypoxia. Hyperventilating hyperthermic animals (temperature > 1050 F) must be cooled. Sedation with acepromazine intravenously is indicated (0.1 mg/kg with a maximum dose of 3 mg) if the animal is still stressed. Fluid therapy is administered with caution, because some animals with severe upper respiratory

tract obstruction develop pulmonary edema. Diuretics are indicated in these patients. If the patient condition is deteriorating, an emergency tracheostomy is recommended to bypass the upper airway. Temporary tracheostotomy increases the risk of complication nine time in the post-operative period.

Surgical Treatment Laryngeal surgery is directed at removing or repositioning laryngeal cartilages that obstruct the rima glottidis. The surgical procedures commonly used to correct laryngeal paralysis are a unilateral arytenoid cartilage lateralization, aventricular cordectomy and partial arytenoidectomy via the oral or ventral laryngotomy approach, and a permanent tracheostomy. Arytenoid cartilage lateralization is getting the gold standard technique.

Arytenoid Cartilage Lateralization This procedure has been used successfully to treat laryngeal paralysis in cats and dogs.

Arytenoid lateralization has been performed bilaterally or unilaterally. Unilateral arytenoid lateralization is sufficient to reduce clinical signs of laryngeal paralysis. A unilateral lateralization can be performed through a ventral or a lateral incision. It is our preference to perform lateralization through a lateral incision.

The animal is positioned in lateral recumbency for a unilateral lateralization, and a skin incision is made over the larynx just ventral to the jugular groove. The sternohyoid muscle is retracted ventrally to expose the lateral aspect of the thyroid and cricoid cartilages. The larynx is rotated to expose the thyropharyngeal muscle, which is transected at the dorsocaudal edge of the thyroid cartilage. The wing of the thyroid cartilage is retracted laterally. The dorsal cricoarytenoide muscle or the fibrous tissue left is dissected and transected. The joint capsule of cricoarytenoid articulation is partially opened with Metzembaum scissors. The opening oft joint capsule should be minimal to prevent excessive abduction while tightening the suture. The sesamoid band connecting the arytenoid cartilages dorsally is left intact.

The arytenoid cartilage is sutured to the caudo-dorsal part of the cricoid cartilage. This provides an adequate laryngeal airway with only a unilateral tieback. Placement of the suture on the caudo-dorsal part of the cricoid provides a physiologic position of the suture. One 2-0 non-absorbable suture is placed in a simple interrupted suture pattern from the muscular process of the arytenoid cartilage to the caudo-dorsal edge of the cricoid cartilage and tightened to maintain the arytenoid in position. The amount of tension on the suture should be limited to avoid to over abduct the arytenoids cartilage. In cats, it is recommended to use small suture material 3-0 or 4-0 mounted on a pledget to prevent tearing through the cartilage. The arytenoid cartilage does not need to be displaced caudally. It is the authors’ impression that the arytenoid cartilage needs only to be maintained in position and stabilized at inspiration. The wound is closed by suturing the thyropharyngeal muscle and routinely closing the subcutaneous tissue and skin.

At the time of extubation it is important to observe per os the size of the laryngeal opening achieved to ensure that adequate abduction of the laryngeal cartilages has been obtained. Excessive abduction may lead to aspiration of food or fluid.

Complications associated with laryngeal lateralization include aspiration pneumonia, persistent cough exacerbated after drinking, seroma, and breaking of the suture and fragmentation of the arytenoid cartilage. Breaking of the suture and fragmentation of the cartilage induce recurrence of the clinical signs of laryngeal paralysis. Laryngeal lateralization should then be performed on the other side. If the procedure has been performed bilaterally a partial laryngectomy needs to be performed. Seroma formation is very common and is self-limited. Aspiration pneumonia is present in 10 to 20% of the cases. Dogs are at risk for aspiration pneumonia during the rest of their life. The incidence of aspiration pneumonia is more common in bilateral laryngeal lateralization compared to unilateral. In a study, 42% of the dogs with bilateral lateralization experienced an episode of aspiration pneumonia. Metoclopramide peri-operatively can be used to try to reduce the incidence of regurgitation and aspiration pneumonia in the perioperative period. Limited utilization of opiod is also recommended to allow sternal recumbency as soon as possible after surgery. A local skin block with bupivacaine might be valuable to control pain post-operatively and minimize the utilization of opioids.

Water and food should be completely withdrawn after surgery for 24 hours. Two or three meatballs should be delivered 24 hours after surgery under constant direct supervision. If the animal can handle meatballs with aspirating, ice cube and then water can be delivered. The animal should be closely watched for the next 2 weeks. The animal is at risk for aspiration pneumonia for its entire life after surgery. The quality of life of the dogs is significantly improved in the long term.

Permanent Tracheostomy Permanent tracheostomy is a surgical option for the treatment of dogs with laryngeal paralysis. The permanent tracheostomy bypasses the upper airway obstruction without inducing any modification in the size of the rima glottidis. This surgical technique is therefore more valuable for dogs at high risk of aspiration pneumonia (myopathy, megaesophagus, hiatal hernia, gastrointestinal disorder). Animals responded well to the treatment and owners were satisfied. Permanent tracheostomy requires attention and maintenance from the owners.

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BRACHYCEPHALIC AIRWAY SYNDROME Eric Monnet, DVM, PhD, FAHA Diplomate ACVS and ECVS Colorado State University, Fort Collins, Colorado Brachycephalic breeds (Shih Tzu, boxer English and French Bulldog, Pekingese, pug and Boston terrier) have a shortened skull compared to the other breeds. Compression of the nasal passage and distortion of the pharyngeal tissue result in an increase in airway resistance. Brachycephalic airway syndrome includes stenotic nares, elongated soft palate, everted laryngeal saccules and laryngeal collapse. There is a high incidence of hypoplastic trachea found in brachycephalic dogs that contributes to airway distress.

Stenotic nares and elongated soft palate are the primary anatomic components of the syndrome while everted laryngeal saccules with laryngeal collapse are thought to be secondary. Excessive negative pressure generated at inspiration because of stenotic nares creates inflammation and stretching of soft tissue and eventually eversion of the laryngeal saccules and laryngeal collapse. Stenotic or obstructed nares affect the mechanics of the lungs and provoke degenerative changes of the nasal mucous membrane. Severe upper airway obstruction can result in pulmonary edema because of a reduction of intrathoracic pressure. The greatest changes are observed in dogs with partial bilateral nasal obstruction and high nasal resistance. Inadequate pulmonary ventilation due to upper airway obstruction can lead to a reduction of arterial oxygen content. The hypoxia is a potent pulmonary vasoconstrictor to divert away blood from poorly ventilated alveoli.

Pulmonary vasoconstriction and pulmonary hypertension result in cor pulmonale and right sided heart failure.

CLINICAL FINDINGS AND DIAGNOSIS Brachycephalic breeds are presented for excessive noisy breathing and inspiratory dyspnea. Inspiratory dyspnea is exacerbated by exercise and augmentation of the ambient temperature. Some English Bulldogs have been presented for vomiting not associated with meals. An increase frequency of hiatal hernia seems to be present in English Bulldogs with brachycephalic airway syndrome. The mean age for dogs presented is 3 to 4 years old. Many of these animals have a high potential to decompensate and develop acute respiratory distress. Therefore, they must be handled carefully to prevent stress and acute decompensation. It is important to keep the animal calm and in a cool environment.

Supplemental oxygen might be required.

Physical examination of the nares for stenosis should be performed. Breathing pattern should be observed. Brachycephalic dogs are presented with an inspiratory dyspnea that is corrected by open mouth breathing if only the nares are involved in the syndrome. If the soft palate is elongated, the laryngeal saccules and/or the larynx collapse the dyspnea is inspiratory and expiratory. The severity of inspiratory dyspnea depends on the length and congestion of the soft palate and other restrictive or obstructive conditions present.

An obstructive breathing pattern, characterized by a slow inspiratory phase followed by a

rapid expiratory phase is seen frequently in brachycephalic breed even if the airway diameter is not comprised more than 50%. In nonbrachycephalic breed, a reduction of more than 50% of the airway diameter is required to modify the breathing pattern. The greatest airway noise is usually noticed in the larynx. Auscultation of the lung field is difficult because of enhanced upper airway sounds.

A radiological examination of the larynx shows an elongated soft palate protruding in the rima glottidis. It is also important to evaluate the diameter of the trachea in dogs with brachycephalic syndrome. It is very common to diagnose an hypoplastic trachea, which worsens the prognosis. Comparison of the diameters of the thoracic inlet (TI) and the tracheal lumen (TD) makes the diagnosis of tracheal hypoplasia. In normal Bulldogs the ratio TD/TI is 0.106 English Bulldogs have the highest incidence of hypoplastic trachea within brachyocephalic breeds (55%). Thoracic radiographs allow evaluation of lung fields for signs of pulmonary edema, pneumonia and the heart for signs of right-sided dilation. If there is cardiac enlargement an echocardiography and an electrocardiogram are required to evaluate myocardial function and arrhythmias. Diagnosis of hiatal hernia can also be done with radiographs.

Blood work is usually within normal limits since the animals are young at the time of diagnosis. An augmentation of the pack cell volume might be indicative of a mild to moderate hypoxia.

A laryngeal examination is required under light general anesthesia to visualize the soft palate, the laryngeal saccules and the function of the larynx. The soft palate should not extend passed the tip of the epiglottis. Position of the soft palate is influenced by the position of the head, traction on the tongue and presence of an endotracheal tube.

Evaluation of the soft palate should be performed without an endotracheal tube in place and with the tongue in a normal position. Everted laryngeal saccules are white shiny dome shape structures located cranial to the vocal cords. Tonsils should also be evaluated as well as the presence of redundant mucosal folds in the pharynx/larynx. A medial tipping of both corniculate processes both and medial flattening of the cuneiform processes of the arytenoid cartilage characterize a laryngeal collapse. The vocal cords are usually not visualized if the larynx is collapse. Usually the corrective surgery is performed during the same anesthesia because recovery from anesthesia with compromise airways could be life threatening.

Stenotic nares are frequently diagnosed in younger, brachycephalic dogs (less than 2 years) with an overlong soft palate and have a favorable prognosis after surgical treatment. In brachycephalic dogs older than 2 years, stenotic nares are associated with additional airway obstruction, and these patients have a guarded prognosis even with treatment. Surgical treatment is therefore recommended as soon as possible to prevent further deterioration of the animal condition and prognosis. English Bulldogs are not responding as well as the other breeds to surgery probably because of the higher incidence of hypoplastic trachea in this breed.

SURGICAL TREATMENT Stenotic Nares In brachycephalic breed the cartilage plates are short, thick and displaced medially.

Stenotic nares are present in 48% of dogs presented for brachycephalic airway syndrome.

Stenotic nares are frequently found in brachycephalic dogs and interference with inspiration by the obstructed nares leads to secondary airway changes (i.e., everted saccules, laryngeal collapse, tracheal collapse). Stenotic nares have also been reported in cats.

The wing of the nostril is examined to determine the amount of tissue to be removed for optimal airflow. The technique of removing a vertical wedge from the wing of a nostril and extending the incision caudally to include part of the alar cartilage has been useful in eliminating stenosis. The incision is made with a # 11 BardParker blade. The tip of the blade is introduced at the apex of the wedge and directed caudally, with the cutting edge directed medially to the free edge of the wing of the nostril. The apex of the wedge is the pivot point of the flap created to allow the edges of the incision to come together evenly and without tension. The blade is again introduced at the apex of the wedge, and the cutting edge directed ventrolaterally as the tip is pushed in caudally to end at the same point as the first incision. The width of the base of the wedge (free edge) determines the opening of the nostril. The wedge is removed, and the edges are sutured with two or three interrupted sutures performed with 30 or 40 absorbable material using a small halfcircle cutting needle.

The surgical site is kept clean and protected from rubbing (selfmutilation) with an Elizabethan collar. Additional medical care is usually not needed.

Elongated Soft Palate In brachycephalic breed the soft palate extends beyond the epiglottis obstructing the airway passage. Vibration of the soft palate in the pharynx induces inflammation and swelling that will obstruct even more the airway. Approximately 80 per cent of cases of overlong soft palate are found in brachycephalic dogs, English and French bulldogs being the most frequently afflicted. Edematous pharyngeal mucosa and enlarged, protruding tonsils are common. The intention of palate resection is to shorten the soft palate so that its free border lies at the tip of the epiglottis or just covers it with the tongue in a normal position.

The mouth is held open with a mouth gag, and the tongue is extended to provide adequate exposure of the oral pharynx. A pair of malleable ribbon retractors is helpful in moving soft tissues while the resection level is being determined. The free border of the palate is grasped with forceps, and both sides of the palate as well as the oral cavity are swabbed with antiseptic.

The tongue is relaxed, and the point at which the tip of the epiglottis touches the soft palate is noted and marked with a scalpel cut or a sterile felttipped marking pen. The caudo-dorsal part of tonsils can also be used as a cranial landmark for the soft palate. A pair of Allis forceps or a traction suture is placed in the free edge of the palate and retracted rostrally. An absorbable suture (40 to 50) is placed in the mucosa at the lateral edge of the free soft palate. The visualization is not always good in the mouth of

brachycephalic dogs. It will open the surgical field and improve the visualization if the procedure is performed with long and curved instruments. The palate is incised from the lateral traction suture to the reference mark at its midline with a scalpel or scissors while low tension is applied on the forceps and lateral traction suture. The soft palate is completely excised. The incised edge is sutured with a simple continuous pattern, with sutures placed through both the nasal and oral mucosa, 1 mm from the cut edge and 2 mm apart. The layer of muscle is avoided so that the mucosa is pulled over the exposed muscle when the sutures are tightened. The closely placed sutures provide a smooth hemostatic closure and do not shorten the width of the soft palate. Postoperative hemorrhage or edema is minimal.

Everted Laryngeal Saccules Everted laryngeal saccules are most frequently encountered in brachycephalic breeds, with a prolonged history of upper airway obstruction. Everted laryngeal saccules have been present in 48% of the brachycephalic dogs in a study. The mucosa of the laryngeal saccules evertes in the larynx because of the high negative pressure during inspiration.

The prolapse mucosa is edematous and creates a mass in the larynx that contributes to the obstruction of the ventral rima glottidis. Resection of everted saccules is not performed routinely. Correction of other components of the syndrome might result in the reduction of the everted saccules.

A temporary tracheostomy is necessary to ensure an adequate airway during surgery and during postoperative recovery. Temporary tracheostomy allows removal of the endotracheal tube from the surgical site and helps manage the airway after the surgery.

A patient is placed in sternal recumbency with the mouth held open as described for partial laryngectomy. The saccule is grasped with long hemostats or Allis forceps, and rostral traction applied. The saccule is amputated at its base with scissors or a longhandled scalpel. Hemorrhage is minor and controlled by pressure. Avoiding the electroscalpel reduces inflammation Resection of everted saccules is associated with edema and swelling of the larynx.

Dexamethasone intravenously (1 mg/kg) is used to reduce the amount of edema after surgery. The temporary tracheostomy is maintained for 24 hours after surgery. The patient is challenged before removal of the temporary tracheostomy tube.

Laryngeal Collapse Laryngeal collapse occurs as a result of a loss of the supporting function of the cartilages. It represents a very advance form of the brachycephalic airway syndrome. The cuneiform and corniculate cartilages are drawn medially by the excessive inspiratory negative pressure. Laryngeal collapse is a progressive disease in which the prognosis worsens with time. Collectively, stenotic nares, elongated soft palate and everted laryngeal saccules predispose dogs to abnormal stresses within the larynx that lead to progressive distortion and ultimate collapse of the arytenoid cartilages.

Three stages of laryngeal collapse have been described (stages 1 to 3) stage 3 being the most advance. The first stage in the pathogenesis of laryngeal collapse involves eversion of the laryngeal saccules into the cavity of the glottis. This is caused by an abnormal negative pressure created at the glottis during inspiration. The vacuum that develops in

the glottis results from the increased inspiratory effort necessary to ventilate through the stenotic nares or elongated soft palate. Inflammation and edema of the mucosa usually accompany saccule eversion and contribute to the dyspnea. During stage 2, the cuneiform process of each arytenoid cartilage, which normally extends to the caudolateral region of the pharynx during inspiration, loses its rigidity and gradually collapses into the laryngeal lumen. In stage 3, the corniculate process of each arytenoid cartilage, which normally maintains the dorsal arch of the glottis, collapses toward the midline, resulting in complete collapse of the larynx. Loss of laryngeal cartilage rigidity is speculated to contribute to the collapse of the cuneiforme and corniculate process. Dogs with stenotic nares, an elongated soft palate, or everted laryngeal saccules are treated for these conditions first. A dog is allowed to recover, and the clinical response suggests whether further resection is necessary.

Dogs with persistent stage 2 disease, even after resection of the soft palate and nares, may require partial arytenochordectomy to enlarge the laryngeal opening. Dogs with stage 3 laryngeal collapse may not show significant improvement when treated with partial laryngectomy. An alternative treatment for dogs with severe laryngeal collapse that does not improve after resection of the elongated soft palate, stenotic nares, or laryngeal saccules is a permanent tracheostomy.

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LAPAROSCOPY IN SMALL ANIMAL PRACTICE Eric Monnet, DVM, PhD, FAHA Diplomate ACVS and ECVS Colorado State University, Fort Collins, Colorado There is a number of minimally invasive surgical (MIS) procedures that are currently performed using laparoscopy. Many of these procedures require multiple trocar/cannula portals, specific minimally invasive surgical instruments, loop ligatures, clip applicators and monopolar electrosurgery. The techniques described below are the “tip of the iceberg” in as far as the potential for MIS in veterinary medicine. They can be performed in a small animal practice.

Intestinal Biopsy Small intestinal biopsies can be obtained using laparoscopy simply by exteriorizing a piece of intestine through the abdominal wall and then collecting the sample externally as would be done with a standard surgical biopsy. A 5-mm atraumatic grasping forceps with multiple teeth is used to grasp the intestine at the site to be biopsied. It may be necessary to “run” the bowel with two grasping forceps to select a location to biopsy. The antimesenteric boarder is firmly grasped with the forceps. The intestine is then pulled to the cannula. A 3-4 cm loop of intestine is exteriorized. A small full thickness biopsy is then obtained in the same manner as one would use when performing an open abdominal surgical technique. The intestine is then returned to the abdominal cavity. If too much intestine is exteriorized it is difficult to return it to the abdominal cavity through a small incision.

Intestinal Feeding Tube Placement Duodenostomy or jejunostomy feeding tubes can be placed using the laparoscope simply by exteriorizing a respective piece of intestine through the abdominal wall and inserting the tube externally. Once the location of the bowel for tube placement is determined the antimesenteric boarder is firmly grasped with the forceps. The intestine is then pulled close to the cannula in which the intestine will be exteriorized. A 3-4 cm loop of intestine is exteriorized and four stay sutures (4-0 monofilament absorbable) are placed in the intestine to prevent the intestine from falling back into the abdominal cavity. A purse-string suture is placed on the antimesenteric border of the intestine. A number 11 blade is used to puncture the intestine in the middle of the purse-string suture and the jejunostomy feeding tube (5 French for cats and 8 French for dogs) is introduced in the loop of bowel in the aboral direction. The purse string suture is closed and the intestine is returned to the abdominal cavity except for the segment containing the feeding tube. The stay sutures are then used to pexy the intestine to the abdominal wall using 4.0 monofilament absorbable sutures. The abdominal wall is then closed with simple

continuous suture pattern. Subcutaneous tissue and skin are closed in a routine fashion.

The feeding tube exits through the incision.

Intestinal foreign body Single, non-linear foreign body in the jejunum or ileum can be removed under laparoscopy. Dogs or cats with signs of peritonitis are not good candidates for this procedure. The surgical technique is the same as for a jejunostomy tube placement. The loop of intestine with the foreign body is exteriorized and an enterotomy or an enterectomy is performed outside of the abdominal cavity. The loop of intestine is then returned into the abdominal cavity at the end of the procedure.

Gastropexy A preventive gastropexy can be performed using the laparoscope simply by exteriorizing the pyloric antrum region of the stomach through the right abdominal wall.

The animal is placed in dorsal recumbency and the telescope portal is placed on the midline at the level of the umbilicus. A 5-mm atraumatic grasping forceps with multiple teeth is used to grasp the pyloric antrum mid-distance between the lesser and the greater curvature. The pyloric antrum is exteriorized after extension of the cannula site situated behind the last rib on the right side. An incisional gastropexy is then performed.

Ovariohysterectomy /Ovariectomy Ovariohysterectomy or ovariectomy can be performed using laparoscopy in any size dogs. The space in the abdominal cavity of small dogs and cats make the procedure technically difficult. The advantage of this technique is the perceived rapid patient recovery following the procedure and the improved visualization of the ureters and the pedicle for hemostasis.

The procedure is performed on dorsal recumbency and tilting the dog on the right and the left side to expose the ovaries.

Two cannulas are enough to perform an ovariectomy or an ovariohysterectomy.

The ovariohysterectomy is laparoscopically assisted then. The cannula for the endoscope is placed caudal to the umbilicus.

For an ovariohysterectomy the second cannulas is placed caudal in the abdomen.

The ovaries are suspended with a transcutaneous suture on the abdominal wall. Each ovarian pedicle is ligated with either suture, endoclips, electrocautery, or a vessel sealant device. After ligation of both ovarian pedicles, the uterus is exteriorized in the caudal abdomen through the caudal cannula. The cervix is ligated outside the abdominal cavity like during a regular ovariohysterectomy. The cervix is then returned to the abdomen.

For an ovariectomy the second cannula is placed cranial to the umbilicus. The ovarian pedicles are ligated as described above. Another ligature will be placed on each uterine horn before transecting the ovaries from the uterus. Electrocautery or vessel sealant device can be used to transect the uterus at the level of the proper ligament. Both ovaries will be removed through one cannula site.

The enlarged cannula sites are sutured with a simple continuous suture pattern with 2-0 monofilament absorbable suture material. Subcutaneous tissue and skin are closed in a routine fashion. The other cannula site requires only subcutaneous and skin sutures.

Cryptorchid Surgery A testicle that is located in the abdominal cavity can be removed easily with laparoscopy. Laparoscopic vasectomy can also be performed through this technique. The dog is placed in dorsal recumbency. The monitor is placed at the end of the table as described for ovariohysterectomy surgery.

The procedure is performed with two cannulas. One is placed cranial to the umbilicus while the other is caudal to the umbilicus.

The ectopic testicle is usually readily visible upon entering the abdominal cavity.

The ectopic testicle of one side rarely ever crosses the midline but stays lateral to the bladder on the effected side. The testicle is grabbed with a fine tooth grasper and a transcutaneous suture is placed through the abdominal wall to stabilize the ectopic testicle. The vascular pedicle and the vas deference are ligated with a pre-tied suture, clips, or electrocautery. The ectopic testicle is removed through one the cannula holes that generally must be enlarged. The enlarged cannula site is sutured with a simple continuous suture pattern with 2-0 monofilament absorbable suture material.

Subcutaneous tissue and skin are closed in a routine fashion. The other cannula sites require only subcutaneous and skin sutures.

Laparoscopic Cystoscopy Laparoscopic cystoscopy is an alternate method that allows placement of a laparoscopic telescope into the urinary bladder that has been exteriorized through the abdominal wall for examination, biopsy and calculi removal. The technique involves a standard laparoscopic entry with the telescope placement on the abdominal midline cranial to the umbilicus. Once the urinary bladder is visualized a second trocar cannula is placed directly over the urinary bladder at the location of exteriorization. Using atraumatic forceps with multiple teeth the bladder is grasped and pulled into the trocar cannula as described in intestinal biopsy section. Once the apex of the bladder is exteriorized stay sutures are placed from the bladder wall. The bladder is temporally pexied to the abdominal wall. A small incision is made in the bladder wall, the bladder is then flushed with sterile saline and the telescope is introduced into the bladder. Forceps can be placed in the lumen along the telescope to obtain a biopsy or remove calculi. At the conclusion of the procedure the bladder is closed in a standard manner and placed back into the abdomen. The cannula ports are then closed. The pexy is released and the abdominal wall closed in a routine fashion.

Laparoscopy is a minimally invasive technique for diagnostic and surgical procedures. Once the basic technique of laparoscopy is mastered and the appropriate indications are applied to the procedures it becomes a simple and rewarding addition to

small animal veterinary medicine and surgery. As our ability advances newer diagnostic and therapeutic procedures will no doubt be developed.

SURGICAL APPROACHES TO THE THORACIC CAVITY Eric Monnet, DVM, PhD, FAHA Diplomate ACVS and ECVS Colorado State University, Fort Collins, Colorado Thoracic approaches provide access to the thoracic cavity and as such are fundamental techniques for thoracic surgery. Two thoracic approaches, intercostal thoracotomy and median sternotomy, are used most often in small animals. Other thoracic approaches such as rib resection or transsternal thoracotomy are used less often. The choice of a thoracic approach depends mostly on the type of access to the thoracic cavity that is needed.

INTERCOSTAL THORACOTOMY Intercostal thoracotomy is employed when exposure to a specific region of the thoracic cavity is needed. This approach provides good access to thoracic structures in the immediate area of the thoracotomy, but access to structures not in the area of the thoracotomy is limited. As a general rule, intercostal thoracotomy allows access to about one-third of the ipsilateral thoracic cavity and mediastinal structures. Access to structures in the contralateral thorax is very limited when using this approach. The exposure gained by intercostal thoracotomy can be increased approximately 33% by performing two small osteotomies, one dorsal and one ventral, on the rib just cranial or caudal to the intercostal incision. It is not necessary to routinely perform osteotomies of a rib, but the technique is useful on occasion when increased exposure is necessary.

The site of an intercostal thoracotomy may be the third through the tenth intercostal space depending on the structures being exposed. The intercostal spaces most commonly used to approach selected thoracic structures in dogs and cats are listed in Table 1. A lateral thoracic radiograph also can help determine the intercostal space that best exposes a desired thoracic structure. A caudal intercostal thoracotomy may be combined with an incision in the diaphragm to provide exposure to the cranial abdominal cavity. Complications associated with intercostal thoracotomy are uncommon as long as air-tight closure of the intercostal space is achieved.

MEDIAN STERNOTOMY Median sternotomy is the only thoracic approach that allows access to the entire thoracic cavity, and therefore is indicated when exploration of the thoracic cavity is necessary. Structures in the dorsal thoracic cavity such as the great vessels and bronchial hilus are more difficult, but not impossible, to reach when this approach is used. Median sternotomy can be combined with a ventral midline celiotomy or cervical incision if a combined approach to the abdomen or neck is desired.

An important technical consideration when performing a sternotomy is that either the manubrium or xiphoid, or both, should be left intact. Doing so greatly enhances the ability to achieve a stable closure of the sternotomy, and thereby decreases the risk of postoperative complications. Reluctance to use this approach because of a perception that it is associated with excessive postoperative pain or complications is not justified. Pain and complication rates with

this approach are not different from intercostal thoracotomy. In fact, median sternotomy probabily causes less postoperative discomfort than intercostal thoracotomy. Sternotomy and thoracotomy are comparable in the degree of cardiopulmonary impairment that they cause.

Thus, the decision to employ a sternotomy or thoracotomy approach should be based on the kind of access to the thoracic cavity needed, and not on a perception that one approach is superior with regard to intraoperative or postoperative morbidity.

THORACOSCOPY Thoracoscopy is examination of the pleural cavity and its organs with a rigid scope. With the development of high-resolution micro-cameras, video optics, and fiberoptic light delivery systems, clear magnified images of the surgical field can be transferred to a video screen. In combination with minimally invasive surgical instruments, the ability to perform diagnostic and advanced therapeutic procedure is possible.

Thoracoscopy is indicated for exploration of pleural space and biopsy of the pleural surface for a patient with a pleural effusion of unknown origin, partial or complete lung lobectomy, biopsy of the lung, pericardectomy and exploration for the right atrium. Thoracoscopy can also be used to perform biopsies for frozen section to establish a diagnosis prior to thoracotomy. Cranial mediastinal mass may represent a challenge to the clinician to establish a definitive diagnosis.

Therefore, thoracoscopy and frozen section of a biospy from a mass in the cranial mediastinum might help differentiating a lymphoma from a thymoma. Thoracoscopy is used commonly in human thoracic surgery for diagnosis of intra-thoracic neoplasia and staging of oncology patients The basic equipment to perform a thoracoscopy includes a surgical telescope, trocar-cannulas, a basic set of thoracoscopic surgical instruments, a light source, a video camera and a video monitor. Thoracoscopy does not require CO2 insufflation since the rib cage is maintaining the thoracic cavity expanded. Telescope comes with different angles. The most commonly used are the 00-degree and the 300-degree angled telescopes. Laparascope trocar-cannula can be used to perform a thoracoscopy. Since the laparoscope trocar-cannulas have a valve, the thorax is not opened and a control pneumothorax needs to be established. Disposable thoracic cannulas do not have a valve. After insertion of the cannula, the thoracic cavity is opened to room air. The lungs are collapsing and positive ventilation is then required. One-lung ventilation with selective intubation of either the left or the right lungs will allow a better exposure of specific area of the thoracic cavity. Cannulas are placed in a triangular position. The cannula for the thoracoscope can be placed in a sub-xyphoid position. The cannulas for the instruments are then placed in the left and right hemithorax at the level of the 7th intercostal space.

Thoracoscopy can be performed with a trans-xyphoid or an intercostal approach. Transxyphoid approach gives access to the left and right hemithorax after partial resection of the mediastinum. Trans-xyphoid approach is the approach of choice for exploration of the thoracic cavity since the right and the left sides of the thoracic cavity can be visualized. Pericardectomy can be performed with this approach. Intercostal approach requires positioning of the animal in lateral recumbency. Only one side of the thoracic cavity can be explored. However, visualization of the hilus of the lung is better for lung resection, and lymph nodes evaluation. In human thoracic surgery, approach through the thoracic inlet has been described for exploration of the cranial mediastinum.

INTRAOPERATIVE CONSIDERATIONS Thoracic surgery is always associated with some degree of cardiopulmonary compromise during surgery. Thoracotomy and sternotomy differ somewhat in the type of cardiopulmonary compromise they are most often associated with. Because animals undergoing thoracotomy are laterally recumbent, they are more likely to develop congestion of the dependent lung and impairment of pulmonary gas exchange. This tendency is countered by maintaining good ventilation to the dependent lung and by avoiding overzealous administration of crystalloid fluids during surgery. On occasion, positive end expiratory pressure (PEEP), applied by immersing the expiratory portion of the ventilator into 5 to 7 cm of water, may be necessary to maintain adequate gas exchange during thoracotomy. On the other hand, animals undergoing median sternotomy in dorsal recumbency are more likely to develop some degree of cardiovascular compromise during surgery because the weight of non-suspended thoracic structures compresses the base of the heart and impedes venous return. This tendency is compensated for somewhat by volume loading the patient to increase cardiac filling pressures. In the end, while it is useful to be aware of these tendencies, it is most important to closely monitor each animal during surgery and provide supportive therapies that best address specific problems and needs.

Placement of a thoracostomy tube before closure of the thoracic cavity is essential to ensure proper and timely evacuation of the pleural space during and after surgery. Failure to place a thoracostomy tube invites substantial risk of developing life-threatening complications. The period of transition from an open to closed thoracic cavity is especially critical. During this period, inadvertent tension pneumothorax can be avoided by keeping the thoracostomy tube open to atmosphere during initial closure of the thoracotomy. Then, after the closure is airtight, the pleural space can be evacuated and the thoracostomy tube closed. It is also important to be aware that pulmonary compliance can decrease suddenly when the thoracic cavity is closed, and that inspiratory pressures may have to be increased to maintain an adequate tidal volume.

POSTOPERATIVE CARE The period immediately after surgery is critical for animals undergoing thoracic surgery.

Hypoventilation, hypoxemia, hypothermia, acid base disorders, hypotension, shock, and oliguria are among the problems that may arise after surgery. Ventilation may be depressed by anesthetic drugs, pneumothorax, or somatic pain. Hypoventilation causes hypoxemia and respiratory acidosis; neither is well tolerated postoperatively. A tidal volume less than 10 ml/kg measured with a Wright's respirometer suggests that ventilation may be inadequate.

Suspected hypoventilation in the recovery period is confirmed by a PaCO2 > 50 mm Hg. Impaired pulmonary gas exchange resulting from pulmonary shunt or VA/Q mismatch also can cause hypoxemia after surgery. The most common cause of pulmonary shunt or VA/Q mismatch after thoracic surgery is pulmonary congestion. For this reason, it is very important that animals recovering from surgery be turned over at least every two hours as long as they remain laterally recumbent. A PaO2 < 60 mm Hg or PA-aO2 > 25 mm Hg while the patient is breathing room air suggests that serious gas exchange impairment is present. Serious hypoxemia due to impaired gas exchange may require treatment with supplemental oxygen or PEEP therapy.

Animals that are hypothermic after surgery should be slowly surface warmed with warm water bottles or circulating water blankets. Hypothermia, hypovolemia, anesthetic drugs, or pain may

cause varying degrees of hypotension during the recovery period. Appropriate treatment of circulatory compromise with fluids is essential. Titrating fluid therapy to central venous or pulmonary wedge pressure is the best way to ensure adequate volume loading and avoiding overhydration. Ideally, central venous pressure should be maintained between 5 and 10 cm of water in animals with cardiovascular compromise. Animals also should be evaluated for acid base and electrolyte disorders. Urine production should be monitored to assure adequate renal function.

Analgesia is indicated in all animals after thoracic surgery. Selective intercostal nerve block, intrapleural anesthetics, epidural morphine, or parenteral opiate drugs are all viable methods for postoperative analgesia. Chest bandages aid in sealing and protecting a thoracotomy incision, however bandages should be wrapped loosely after thoracic surgery as they can impair ventilation. Placement of a thoracostomy tube during thoracic surgery is always indicated since it allows close monitoring the pleural space for the presence of air or blood during the recovery period. The thoracostomy tube should be hand-aspirated every hour for four hours, and then every two to four hours until it is removed.

TABLE 1:

Location of Thoracic Structures via Intercostal Thoracotomy Thoracic Structure

Intercostal Space Left

Right

Heart and pericardium Ductus arteriosus Pulmonic Stenosis Pericardiectomy

4, 5 4, 5 4 5

4, 5

Lungs

4-6 4, 5 5, 6

4-6 4, 5 5 5, 6

3-5 7-9

3-5 7-9

Cranial lobe Middle lobe Caudal lobe Esophagus Cranial Caudal Thoracic Duct Dog Cat

5

8-10 8-10

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SURGERY OF THE LUNG Eric Monnet, DVM, PhD, FAHA Diplomate ACVS and ECVS Colorado State University, Fort Collins, Colorado The trachea divides into two principle bronchi which in turn subdivide into lobar bronchi that supply each lung lobe. Within each lung lobe, lobar bronchi divide into segmental bronchi that supply bronchopulmonary segments within each lobe. Dichotomous branching of the airway continues through subsegmental bronchi, terminal bronchioles, and respiratory bronchioles.

Respiratory bronchioles give rise to alveolar ducts, alveolar sacs, and pulmonary alveoli. The pulmonary arteries follow a lobar distribution in close proximity to the cranial dorsal aspect of each bronchi. Bronchial branches of the bronchoesophageal arteries provide oxygenated blood to the airways down to the level of the respiratory bronchioles where they terminate in capillary beds continuous with the pulmonary arteries. Pulmonary veins course on the caudal and ventral aspect of each bronchi collecting blood from both the pulmonary and bronchial arteries.

The left lung of dogs and cats is divided into cranial and caudal lobes. The left cranial lung lobe is divided into a cranial and caudal portion, but shares a common lobar bronchus. The right lung is divided into four distinct lobes: cranial, middle, caudal and accessory. The accessory lobe passes dorsal to the caudal vena cava and is located medial to the plica vena cava.

PNEUMOTHORAX Pneumothorax results from the accumulation of air in the pleural space. The air can come from the respiratory tract, the esophagus and through the skin. Spontaneous pneumothorax are classified as primary or secondary. Primary pneumothorax are usually resulting from the rupture of a bleb or a bullae. Primary spontaneous pneumothorax are more common in large breed dog with deep chest. Secondary spontaneous pneumothorax results from a lung pathology that eroded through a bronchioles (pneumonia, abscess0 or from chronic obstructive lung disease (emphysema). Primary spontaneous pneumothorax are treated with drainage of the pleural space by thoracocenthesis or thoracostomy tube. If a bullae is visible on thoracic radiographs, a lung lobectomy is then recommended. A pleurodesis can also be performed at the time of surgery to prevent recurrence.

NEOPLASIA Primary neoplasia of lung is the most common indication for pulmonary surgery in small animals.

Presumptive diagnosis of primary lung neoplasia is based on characteristic radiographic appearance of a solitary lung mass. Fine needle aspiration can be undertaken prior to surgery. Pulmonary lobectomy is indicated for suspected primary lung tumors without prior biopsy. Excision biopsy of hilar lymph nodes is indicated for staging if they are visualized.

Diagnosis is confirmed by histopathologic examination of the excised specimen.

Adenocarcinoma is the most common primary lung neoplasia in dogs, representing approximately 75% of the cases. Alveolar carcinoma and squamous cell carcinoma also occur.

Pulmonary carcinomas are classified as differentiated or undifferentiated. Prognostic indicators

for primary lung neoplasia include involvement of hilar lymph nodes at surgery, histologic type, tumor size, and presence of pleural effusion. The prospect for cure or long term remission with surgery alone is good for small differentiated adenocarcinomas. Undifferentiated carcinomas have over a 50% incidence of metastasis. The prognosis for squamous cell carcinoma is poor with a metastasis rate of over 90%.

Metastatic lung neoplasia is treatable by surgical excision under certain circumstances.

Guidelines for surgical treatment of metastatic pulmonary disease include: control of the primary site for at least several months, no evidence of metastasis to sites other than lung, favorable histology (i.e. sarcomas are better than carcinomas), slow growth of metastatic tumors (i.e. size doubling time > 30 days), and less than 5 metastatic nodules present. Metastatic lung tumors should be excised by partial lung resection whenever possible to preserve lung volume.

LUNG LOBE TORSION Lung lobe torsion is a rare condition that occurs most often in large deep-chested dogs. The condition may occur secondary to one of several predisposing factors including thoracic trauma, pleural effusion, diaphragmatic hernia, pneumothorax, or thoracic surgery. Lung lobe torsion occurs most often in the right middle lung lobe and less often in the left cranial lung lobe.

Clinical findings associated lung lobe torsion include acute depression, weakness, dyspnea, tachypnea, cyanosis, nonproductive cough, hemoptysis, and tachyarrhythmias. Radiographically, lung lobe torsion appears as an isolated atelectasis of the right middle or left cranial lung lobes.

Air bronchograms may be present early, but disappear over time. Pleural effusion is often apparent on radiographs. Evacuation of sanguinous effusion fails to expand the collapsed lobe.

Confirmation of the diagnosis can be made by contrast bronchography, bronchoscopy, or exploratory surgery. At surgery, the involved lung lobe appears as a solid liver-like mass due to engorgement of the lung with blood. Surgical treatment consists of complete lung lobectomy of the affected lung, preferably without derotation of the lung lobe.

PULMONARY ABSCESS Pulmonary abscesses occur secondary to severe pulmonary infections or pulmonary foreign bodies. Foreign bodies can enter by inhalation or impalement through the thoracic wall.

Pyothorax can occur concurrently with pulmonary abscesses. Persistent pulmonary atelectasis and signs of pneumonia despite appropriate antibiotic therapy suggests the presence of a pulmonary abscess. Pulmonary lobectomy of the affected lung lobe is indicated for suspected pulmonary abscesses. Caution during surgical manipulation of an abscessed lung lobe is necessary to prevent expulsion of purulent material into adjacent lung lobes. Morbidity and mortality associated with this procedure is high in animals that have active diffuse pneumonia at the time of surgery.

PULMONARY RESECTION TECHNIQUES Possible indications for pulmonary resection include pulmonary neoplasia, pulmonary trauma, pulmonary abscess, lung lobe torsion, bronchoesophageal fistula, and spontaneous pneumothorax. Normal animals can tolerate resection of as much as 50% of their lung capacity and still survive. However, generalized pulmonary disease substantially decreases the amount of

lung resection that can be tolerated.

Chronic obstructive lung disease and pulmonary hypertension in particular limit the extent of pulmonary resection that can be undertaken.

Lung Lobectomy Lung lobectomy is indicated for severe traumatic injury, neoplasia, lobe torsion, or abscesses that are primarily confined to a single lung lobe. Lung lobes that can undergo separate lobectomy in small animals include the left cranial, left caudal, right cranial, right middle, and right caudal lobes. The accessory lobe divides incompletely from the right caudal lobe and generally is resected with the caudal lobe. The standard surgical approach for lung lobectomy is a fifth intercostal thoracotomy in dogs and a sixth intercostal thoracotomy in cats. The procedure can be performed one intercostal space cranial or caudal to the ideal intercostal space, if necessary. Lung lobectomy also can be accomplished from a median sternotomy, if this approach is indicated for other reasons. Lung lobectomy is performed by dividing the pulmonary vessels and oversewing the lobar bronchus. Lung lobes should be manipulated carefully during resection to avoid embolization of neoplastic cells or extrusion of purulent material into adjacent airways. The bronchus should be checked for leaks after closure by flooding the chest with saline and applying a positive pressure breath. Placement of a thoracostomy tube prior to closure of the thoracotomy is absolutely indicated.

Partial Lung Resection Partial lung resection is indicated for lung biopsy or excision of localized pulmonary lesions that do not require complete lung lobectomy. Partial lung resection can be performed by a standard suturing technique or with a surgical stapling device. Standard partial lung resection can be accomplished with readily available materials, but some leakage of air from the surgery site can be anticipated after surgery. Stapling devices, when available, are fast and less likely to leak after surgery. Partial lung resection can be performed using either the TA or GIA surgical stapling device. The 3.5 mm (blue) staples are most appropriate for stapling lung tissue. Any leakage of air after surgery is readily evacuated by a thoracostomy tube and usually will be self limiting after several hours.

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PLEURAL EFFUSIONS Eric Monnet, DVM, PhD, FAHA Diplomate ACVS and ECVS Colorado State University, Fort Collins, Colorado

The thoracic cavity is lined entirely by a serous membrane known as pleura. The pleura is divided into visceral pleura which covers the lungs and parietal pleura which covers the remaining thoracic cavity. The pleura is composed of a single layer of mesothelial cells supported by a delicate network of elastic connective tissue. The visceral and parietal pleura contain a rich capillary network that originates from the pulmonary and systemic circulations, respectively. In addition, the parietal pleura contains a rich lymphatic network responsible for lymphatic drainage of the pleural space. Under normal conditions, the pleural space is only a potential cavity. The visceral and parietal pleura are separated by a thin layer of pleural fluid, the average volume of which is 2.4 ml in a 10 kg dog. Liquid coupling between the thoracic wall and lungs provides instantaneous transmission of thoracic volume changes to the lungs, and yet allows low friction sliding between the pleural surfaces.

Because high pleural permeability causes the pleural space to be continuous with the interstitial fluid of the thoracic wall, the dynamics of pleural fluid formation and absorption are controlled by Starling's forces. Since hydrostatic pressure in the systemic capillaries that supply the parietal pleura is a 30 cm of water and hydrostatic pressure of the pulmonary capillaries that supply the visceral pleura is approximately 11 cm of water, one theory suggests pleural fluid is formed by the parietal pleura and absorbed by the visceral pleura under physiologic conditions.

More recent evidence suggests that pleural fluid filters through the parietal pleura and is drained by parietal lymphatics.

HYDROTHORAX Hydrothorax is the result of transudative effusion caused by a disturbance in the balance of Starling forces responsible for pleural fluid formation and absorption. Hypoalbuminemia reduces capillary colloid osmotic pressure and causes fluid to remain in interstitial compartments including the pleural space.

Congestive heart failure causes hydrothorax by disturbing pulmonary and systemic capillary hydrostatic pressures. Right-sided congestive heart failure increases pleural fluid formation, whereas left-sided congestive heart failure decreases pleural fluid absorption. Hydrothorax may result from obstruction of venous or lymphatic drainage such as occurs with lung lobe torsion or incarcerations of liver through a diaphragmatic herniation.

These effusions result from transudation of fluid through the organ capsule.

Diagnosis of hydrothorax is based on identification of an effusion as a transudate or modified transudate. Transudates typically have a specific gravity less than 1.018, a total protein less than 1.5 gm/dl, and a nucleated cell count less than 3 X 103 cells/ul. Large (5-20 u) pale staining mesothelial cells predominate comprising 70% of the nucleated cell count. Single mesothelial cells are most common, although multicellular clusters of mesothelial cells are occasionally observed and must be differentiated from neoplastic cells. Macrophages and

lymphocytes account for the remaining nucleated cells. As a transudative effusion becomes longstanding, mesothelial cells degenerate and attract neutrophils to the pleural space. Total nucleated cell counts may approach 5 X 103 cells/ul with a significant percentage of the cells being neutrophils. These effusions are termed modified transudates. Effusions associated with obstructive phenomenon such as lung lobe torsion or liver incarceration present a distinctive picture on fluid analysis. Because the obstructive process causes lymphatic as well as venous obstruction, the effusions generally will have a total protein of 1.5 to 5 gm/dl. Red blood cells and lymphocytes often are present in numbers higher than is typical for a transudate. Pleural effusions with these characteristics are termed high-protein modified transudates or obstructive effusions. These effusions quickly develop an inflammatory component if organ necrosis is occurring. The treatment of hydrothorax consists of pleural drainage if respiratory distress is present and correction of its underlying cause if possible.

PLEURITIS AND PYOTHORAX Inflammatory conditions of the pleura may be dry, serofibrinous, pyogranulomatous, or purulent. Dry pleuritis often precedes inflammatory pleural effusions. Dry pleuritis may be caused by bacteria, viruses, or trauma. A diagnosis of dry pleuritis is suggested by clinical findings of a rapid and shallow respiratory pattern, obscure thoracic pain, nonproductive cough, and auscultation of a pleural friction rub.Serofibrinous pleuritis is reported with canine hepatitis, canine leptospirosis, canine distemper, canine and feline upper respiratory viruses, and parasitic diseases such as Aelurostrongylus in cats and Spirocerca lupi in dogs. Bile and tuberculosis are unusual causes of severe serofibrinous pleuritis. Pyogranulomatous pleuritis is associated with feline infectious peritonitis. The effusion is secondary to virus-induced vasculitis affecting all serous membranes.Purulent pleuritis, also referred to as pyothorax or empyema, is invariably the result of bacterial or fungal sepsis of the pleural space. Sources of bacterial contamination include penetrating thoracic wounds, extension of bacterial pneumonia, migrating foreign bodies, esophageal perforations, extension of cervical, lumbar or mediastinal infections, and hematogenous spread. Thoracic bite wounds are frequently implicated in feline pyothorax.

Inhalation and migration of a grass awn often is suspected in field dogs with pyothorax.

Anaerobic bacteria and Nocardia asteroides are isolated most often from dogs with pyothorax.

Pasteurella multocida and anaerobes are the most prevalent isolates in cats.

Pleuritis and pyothorax frequently have an insidious course and presentation may be delayed. Moderate to severe respiratory distress usually is present. The patient also shows signs of systemic infection characterized by anorexia, weight loss, malaise, and fever. Physical and radiographic findings are those of pleural effusion. Inflammatory exudates typically exhibit a total protein greater than 3.0 gm/dl, a specific gravity greater than 1.018, and a total cell count greater than 30 X 103 cells/ul. Inflammatory exudates may be nonseptic or septic.Nonseptic exudates usually have a serofibrinous or serosanguineous appearance. Feline infectious peritonitis produces a nonseptic exudative pleural effusion that appears yellow, translucent, and viscous on gross examination. Total protein values will approach serum levels ranging from 4 to 8 gm/dl. Electrophoresis will reveal an elevated gamma globulin fraction. The predominant cell types present in nonseptic exudates are nondegenerative neutrophils and macrophages. Total cell counts are generally not high, ranging from 5 to 15 X 103 cells/ul. Septic exudates are

characteristic of pyothorax. The fluid is viscous, opaque, and varies in color from white or yellow to green or red. The fluid may clot or exhibit fibrinous debris, and often produces a foul odor. Cell counts range from 30 to 200 X103 cells/ul, although accurate cell counts are difficult due to extensive cellular degeneration. Degenerate neutrophils predominate and bacteria are often visualized. Gram stains may give an early indication of the types of bacteria present. Fluid should be cultured for aerobic and anaerobic bacteria. Macrophages and plasma cells increase as an exudative process becomes longstanding.

Treatment of pyothorax must be prompt and aggressive. The prognosis is guarded but not hopeless. The initial goal of therapy is to relieve respiratory embarrassment by thoracocentesis, preferably under minimal restraint with the patient sternal or standing. Supportive care with intravenous fluids is necessary to correct dehydration, acid-base and electrolyte imbalance.

Systemic antibiotic therapy should be initiated immediately, and then adjusted based on culture and sensitivity results if necessary. Success in culturing anaerobic bacteria is dependent on sample handling. Samples must be submitted in a capped syringe within one hour or in appropriate transport media within 24 hours. Due to the high incidence of anaerobic infections, antibiotics with an anaerobic spectrum should be started upon diagnosis of pyothorax and continued throughout the course of disease. Many animals with pyothorax will have bacteremia or septicemia so intravenous antibiotics are indicated in the initial treatment period. Oral antibiotic therapy should be continued for at least four to six weeks after diagnosis. Once the patient is stable, a thoracostomy tube should be placed utilizing local anesthesia and sedation.

Bilateral thoracostomy tubes often will be necessary. After complete evacuation of the pleural space, pleural lavage is initiated.

The pleural space should be lavaged twice daily with approximately 20 ml/kg of warmed 0.9% saline or Ringerâ&#x20AC;&#x2122;s solution. The lavage fluid should be instilled slowly and discontinued if respiratory distress occurs. The lavage fluid should remain in the pleural space for one hour if respiratory distress does not occur. Approximately 25% of the initial lavage volume will be absorbed by the patient. Efficacy of treatment is monitored by clinical findings, thoracic radiographs, and cytology of the pleural effusion. Most animals with successful treatment will have a decrease in fever and improvement in general attitude within the first 48 hours. Cytology of pleural fluid can be used to assess the response to therapy.

Neutrophils, both total number and percentage of degenerate cells, and bacteria should gradually subside over three to five days. The combination of thoracostomy tube, pleural lavage, and antibiotic therapy have been reported to resolve 50 to 60% of cases of pyothorax in small animals.

Lack of significant clinical improvement within 48 to 72 hours or radiographic demonstration of undrained encapsulated fluid are indications to surgically explore the thoracic cavity. Radiographic evidence of lung lobe consolidation and pneumothorax suggest the possibility of a ruptured pulmonary abscess and is a relative indication for surgery. Exploratory thoracotomy should be undertaken by medium sternotomy which gives access to both hemithoraces. Adhesions and loculated pockets of fluid should be broken down carefully during surgery. Mediastinectomy often is necessary since the ventral mediastinum is invariably thickened and filled with small abscesses (Figure 8.1). The pericardium also may require excision if it is thickened and abscessed. Consolidated lung lobes which cannot be inflated

should be excised by partial or complete lobectomy. Large lung lacerations created by adhesion breakdown must be repaired or the damaged tissue excised. Before closure, the thoracic cavity is vigorously lavaged with copious amounts of warm isotonic crystalloid solution. Closed pleural lavage should be continued postoperatively for at least two to three days. The probability of success with surgical management of refractory pyothorax is better for dogs than for cats.

Constrictive pleuritis is a serious sequela to longstanding pyothorax that is suggested by an inability to re-expand the lungs following resolution of the pyothorax. If the constriction is diffuse, then surgical decortication of the fibrous peel from the visceral pleura is necessary (Figure 8.2). Decortication in small animals is a difficult surgical procedure, but it can be successfully accomplished with careful technique. The procedure often results in numerous pulmonary lacerations that should be treated with continuous pleural drainage postoperatively.

Decortication should be attempted as soon as possible after it is recognized.

CHYLOTHORAX

Chylothorax results when chyle from the cisterna chyli-thoracic duct system gains access to the pleural space. In the dog, the caudal thoracic duct courses dorsal and to the right of the aorta, lateral to the intercostal arteries, and ventral to the azygos vein. The duct crosses to the left side of the aorta ventral to the body of the fifth thoracic vertebra and continues cranioventral across the left side of the esophagus to empty at the junction of the left jugular vein and cranial vena cava. Although this description of the thoracic duct is considered "normal", few dogs exhibit this pattern without some variation. Variations included multiple collaterals of the caudal and middle portions of the duct, and double duct systems. In the cat, the caudal thoracic duct typically courses dorsal and to left of the aorta.

The etiology of chylothorax is poorly understood in the dog and cat. The incidence of chylothorax in Afghan is inordinately high, but it is unknown if this predisposition is hereditary.

Trauma is an often cited cause of chylothorax in dogs and cats. Thoracic duct rupture might result from blunt or penetrating injuries, traumatic diaphragmatic herniation , thoracic surgery, or severe coughing or vomiting episodes. Recent evidence suggests that traumatic rupture of the thoracic duct may be an uncommon cause of chylothorax in animals. The role that obstruction of the thoracic duct plays in the development of chylothorax is unclear. Experimental obstruction of the thoracic duct alone rarely results in chylothorax, but ligation of the cranial vena cava produces lymphangiectasia of the thoracic duct and a high incidence (> 50%) of chylothorax in dogs and cats. It is speculated that lymphangiectasia may allow extravasation of chyle through the lymphatic vessel wall. Malignancies or thrombosis that occludes the cranial vena cava might induce chylothorax by such a mechanism. Elevations in systemic venous pressure secondary to congestive heart failure likely explain why chylothorax occurs with cardiomyopathy, tricuspid dysplasia, and heartworm disease. Lymphangiectasia of unknown origin has been demonstrated in dogs and cats with spontaneous chylothorax.

Debilitation associated with chylothorax is caused primarily by loss of chyle from the body after pleural drainage is instituted. Water and electrolyte losses can be sufficient to cause dehydration and electrolyte imbalance. Loss of lipid and protein can lead to protein-calorie malnutrition and hypoproteinemia. Malnutrition is compounded by the loss of fat soluble

vitamins. Immunocompetence becomes impaired due to loss of antibodies, lymphopenia, and malnutrition.

Diagnosis of chylothorax is based on recognition of characteristic clinical and radiographic findings of pleural effusion and by demonstration of chyle on fluid analysis. Chylous effusions are typically opaque and milky white to yellow in color. Chyle retains its milky appearance upon standing and may form a creamy top layer. Physicochemical properties of chylous effusions are similar to obstructive transudates since lymph composes a large portion of thoracic duct chyle.

Total protein ranges from 3 to 5 gm/dl. Cytological examination reveals a predominance of small and large lymphocytes.

Chronic chylous effusions will show increased neutrophils, macrophages, and mesothelial cells. Total cell counts generally do not exceed 20 X 103 cells/ul.

Chylomicrons within an effusion confirms its chylous nature. Chylomicrons can be visualized on direct smears or with supravital stains such as Sudan III or IV. The presence of chylomicrons is most reliably confirmed by determination of triglyceride levels in the serum and fluid. Chylous fluids typically show triglyceride levels that are 12 to 100 times greater than levels measured in the serum. Cholesterol levels in chylous effusions are not elevated when values are compared to values from serum. Anorectic animals with chylous effusion may have greatly reduced levels of chylomicrons. Pleural fluid from such animals may easily be mistaken for a modified transudate or obstructive effusion. Feeding a fatty meal is often necessary to demonstrate the chylous nature of a pleural effusion in these animals.Pleural effusions high in cholesterol or lecithin-globulin complexes appear grossly similar to chylous effusions, but are due to degenerating cells associated with chronic inflammatory or malignant processes. These effusions are termed pseudochylous effusions. Pseudochylous effusions will be low in triglycerides and may have a high cholesterol level.

Once chylothorax is diagnosed, an attempt to determine its cause should be undertaken.

Owners should be questioned regarding the possibility of recent trauma. Thoracic radiographs taken after complete pleural drainage should be evaluated for the presence of masses particularly in the cranial mediastinum. Echocardiography and ultrasound examination of the mediastinum also can be undertaken. Animals with chylothorax should be evaluated for dirofilariasis using microfilaria concentration techniques or serum adult antigen detection tests, or both. Cytologic examination of the chylous effusion for the presence of neoplastic cells helps rule out neoplasia.

Often, a cause for chylothorax is not found and the clinician is left with a diagnosis of idiopathic chylothorax. Direct lymphangiography may provide information on the etiology of idiopathic chylothorax (i.e rupture versus lymphangiectasia), but generally is of academic interest only since it usually does not change the therapeutic plan.

Treatment of chylothorax may be medical or surgical. Medical management is directed at draining the pleural space and reducing the formation of chyle. Pleural drainage is indicated to relieve respiratory distress and may either be intermittent or continuous. Low-fat diets decrease the triglyceride content of chyle, but there is no evidence that the volume of chyle is similarly decreased. Animals with chylothorax should receive aggressive nutritional support and be supplemented with fat soluble vitamins.

Surgical management of chylothorax involves ligation of the caudal thoracic duct. The rationale for ligation of the thoracic duct is based on formation of lymphaticovenous

anastomoses that divert chyle flow away from the thoracic duct system. Absolute indications for surgical intervention are not established in animals. The following indications for surgery are suggested: 1) failure to significantly diminish the flow of chyle after 5 to 10 days of medical management, 2) losses of chyle exceeding 20 ml/kg/day over a five day period, or 3) proteincalorie malnutrition and hypoproteinemia. Transthoracic ligation of the thoracic duct is accomplished through a right ninth or tenth intercostal thoracotomy in the dog. Failure to ligate all collateral branches of the caudal thoracic duct is thought to be a most common cause of operative failure. For this reason, en bloc ligation of all structures in the caudal mediastinum dorsal to the aorta is recommended. Intraoperative lymphangiograms performed to ensure complete ligation of the thoracic duct have been advocated, however this approach substantially increases operative time and requires facilities for taking intraoperative radiographs. The success rate for surgical management of chylothorax alone is generally less than 60%. Combined mechanical pleural pleurodesis and thoracic duct ligation, both performed via median sternotomy, is currently undergoing clinical evaluation and shows early promise for improving the success of surgery.

Despite vigorous attempts at medical and surgical management, a significant number of animals with chylothorax will fail to respond to therapy. Pleuroperitoneal shunting and chemical pleurodesis have been advocated as palliative treatments for refractory chylothorax. Chronic chylothorax can cause a constrictive pleuritis that may require decortication.

HEMOTHORAX

The most common cause of hemothorax is trauma, either accidental and surgical.

Coagulopathies including thrombocytopenia or warfarin toxicity also can manifest with hemothorax as a primary finding. Neoplasia or parasites, e.g. Spirocerca lupi and Dirofilaria immitus, can cause rupture of thoracic vessels and spontaneous hemothorax.

Diagnosis of hemothorax is based on demonstration of blood in the pleural space.

Specific gravity, total protein, total cell counts, and cytologic findings of hemorrhagic effusions are similar to values in the peripheral blood. The myeloid-erythroid ratio is approximately 1 to 100, similar to peripheral blood. Hemorrhagic effusions generally will have a hemoglobin level of at least 25% of the blood level, whereas serosanguineous effusions rarely have hemoglobin values exceeding 1 gm/dl. Hemorrhage within the pleural space generally does not clot due to mechanical defibrination and activation of fibrinolytic mechanisms. Clotting also is impaired by the disappearance of platelets within eight hours following hemorrhage.

Diagnostic evaluation of coagulation parameters is indicated in animals with hemothorax, especially in the absence of obvious trauma. A platelet count and activated clotting time should be performed. If a platelet count and activated clotting time are normal but coagulopathy is still suspected, a mucosal bleeding time should be performed to assess platelet function particularly in breeds that commonly have von Willebrandâ&#x20AC;&#x2122;s disease. A citrated blood sample should be collected before blood transfusion, centrifuged immediately, and frozen for future assessment of specific factor deficiencies if needed.

Hemothorax is a common injury associated with thoracic trauma. Hemorrhage can originate from internal structures such as the heart, great vessels, or lungs, or from laceration of

intercostal or internal thoracic arteries. Treatment of hemothorax depends on the volume and flow of hemorrhage in the pleural space. Dogs are capable of complete resorption of their blood volume from the pleural space within 90 hours. Therefore, mild hemothorax that does not induce significant respiratory distress should be managed conservatively to allow resorption of pleural blood. Occasionally, pleural hemorrhage is sufficient to require pleural drainage for relief of respiratory embarrassment. Animals with substantial blood loss from the pleural space may require blood transfusion in addition to crystalloid volume replacement to maintain an adequate packed cell volume. Autotransfusion of autogenous blood removed by pleural drainage provides a readily available source of compatible blood in patients with severe hemothorax. Blood can be collected directly into a standard blood collection bag and returned to the patient by standard gravitational infusion. Blood collected into 60 ml syringes should be anticoagulated with citrate phosphate dextrose (CPD) or of anticoagulant citrate dextrose (ACD) (8 to 10 ml/100 ml blood).

Autogenous blood should be administered with a standard blood administration set. Filtration of autotransfused blood with a micropore filter has been recommended to remove microthrombi.

However, due to the expense of these filters and a lack of observed problems when they are not used, standard blood filtration is usually used in animals. Potential problems associated with autotransfusion include microembolization, hemolysis, and coagulopathy.

Despite these problems, autotransfusion is a practical and lifesaving procedure for animals with severe hemothorax. Rarely pleural hemorrhage will be such that pleural drainage and autotransfusion cannot keep ahead of accumulation. In this case, exploratory thoracotomy is indicated in an attempt to repair the site of hemorrhage. Exploratory thoracotomy should be undertaken by a median sternotomy approach. If exploratory surgery for severe hemothorax is undertaken, the surgical team should be prepared for intraoperative collection of blood for autotranfusion.

Occasionally, chronic hemothorax can organize to form a fibrous pleural peel that may require decortication. Decortication is ideally performed within five weeks of hemothorax before fibrous infiltration of the visceral pleura has occurred.

NEOPLASTIC EFFUSION

Pleural effusion can result from primary or metastatic neoplasia involving the thoracic cavity. Lymphosarcoma, pulmonary carcinoma, metastatic carcinomas, and hemangiosarcomas have all been reported to cause neoplastic effusions. Mesotheliomas are rare in all species, but are associated with pleural effusion when present.

Neoplastic effusions are suspected when physical, radiographic, and laboratory findings suggest the presence of a thoracic neoplasm. Neoplastic effusions may have either a exudative or transudative fluid pattern and are identified by the presence of neoplastic cells on cytological examination. Thymic lymphosarcoma is the most common cause of neoplastic effusions in cats.

Neoplastic lymphocytes are usually prolymphocytes or lymphoblasts. These cells are large, variable in size, and have intensely basophilic cytoplasm and multiple nucleoli. Metastatic carcinomas and occasionally sarcomas will produce neoplastic effusions. Differentiation of neoplastic cells from reactive mesothelial cells is difficult even for experienced cytologists.

Therefore, care must be used in diagnosing neoplasia on cytologic examination alone. Cytologic findings should be correlated with other clinical findings. A punch biopsy of the pleura is indicated when pleural neoplasia such a mesothelioma is suspected.

Treatment of a neoplastic pleural effusion is directed at the causative neoplasm. The prognosis for animals with neoplastic effusions is poor with the exception of effusions associated with lymphosarcoma. Intermittent pleural drainage gives temporary relief from respiratory distress. Intracavitary chemotherapy or radionucleotides have been used in the management of neoplastic effusions in dogs. Pleurodesis also may be considered for palliation of neoplastic effusions.

PATENT DUCTUS ARTERIOSUS Eric Monnet, DVM, PhD, FAHA Diplomate ACVS and ECVS Colorado State University, Fort Collins, Colorado Congenital heart defects are the most common indication for considering cardiac surgery in small animals. Congenital heart defects result in pathophysiologic alterations that can lead to progressive heart failure, sudden death, or severe hypoxemia. For most of the congenital heart defects more than one surgical option is available. The options depend on the nature and the severity of the defect, and financial constraints. The surgical options are either a closed heart or an open-heart technique. Closed heart techniques provide most of the time a palliative treatment for the defect while open technique will provide more a curative treatment.

Patent Ductus Arteriosus (PDA) is the most common congenital heart defect seen in dogs. It is also present in cats. Poodles Shelties, German Shepherds, Collies, Pekinese and Welsh Corgies are the most common breed presented for PDA. Females are over represented.

Ductus arteriosus establishes a communication between the pulmonary circulation and the systemic circulation in the fetus. The lungs in the fetus are non-functional and the pulmonary circulation is a high pressure system. Oxygenated blood coming from the placenta can bypass the lung and perfused the fetus. Ductus arteriosus physiologically closed at birth when the lungs expand and the pulmonary artery resistance drops.

Prostaglandins are involved in the closure of the ductus. The ductus arteriosus is anatomically closed at 2 weeks.

Patent ductus arteriosus induces a left to right shunt, which results in volume overload of the left heart. Volume overload of the left atrium and ventricle results in left ventricular dilation and hypertrophy. During diastole, pressure in the aorta drops very low because the blood shunts into the low pressure system of the pulmonary circulation.

Cardiac output is maintained by augmentation of stroke volume with fluid retention.

Progressive left ventricular dilation induces a mitral regurgitation with a more severe volume overload of the left ventricle. If untreated the dogs will develop left-sided congestive heart failure with pulmonary edema. Atrial fibrillation can develop later.

Dogs with PDA can also develop pulmonary hypertension a reverse flow can occur in the PDA when pulmonary pressures are superior to systemic pressures. This condition occurs rarely. It induces cyanosis.

Diagnosis Dogs with PDA will present a continuous murmur over the left heart base and a strong femoral pulse. A palpable cardiac thrill often is present. The murmur is usually first heard during a vaccination visit.

Dogs with severe dilation and advance mitral

regurgitation are presented with signs of congestive heart failure: difficulty breathing, cough and exercise intolerant. A separate holosystolic heart base murmur might be heard when the mitral regurgitation is severe. Dogs with a reverse PDA will be presented for exercise intolerance, and hind leg weakness. The patient is cyanotic. The cyanosis is more pronounced in the caudal half of the animal. The femoral pulse is usually normal.

No cardiac murmur is present especially if polycythemia is present.

Thoracic radiographs show left atrial and ventricular enlargement, enlargement of the pulmonary circulation, and a dilation of the descending aorta. Pulmonary edema can be visible in the patient in early congestive heart failure.

Echocardiography confirms the left ventricular and atrial dilation. Myocardial function is usually normal. Ejection fraction is reduced when congestive heart failure develops.

The mitral regurgitation can be evaluated with Doppler echocardiography. Turbulences are visible in the pulmonary artery with color Doppler echocardiography. The pulmonic stenosis or insufficiency is not present. Sometimes the ductus arteriosus can be visualized on the echocardiography.

Surgical treatment Surgical correction of a left to right PDA is accomplished by ligation or occlusion of the ductus arteriosus. If the patient is presented with pulmonary edema it should be treated with furosemide for 24 to 48 hours prior to surgery. Surgical treatment is a cure for this congenital heart defect. If the ductus is not occluded the animal will dye of congestive heart failure at 1 or 2 years old. Some animal will develop pulmonary hypertension at a younger age if they have a predisposition.

Surgical technique for ligation The animal is placed in right lateral recumbency after induction of general anesthesia.

The left side of the thoracic cavity from the cranial point of the shoulder to the last rib is prepared with aseptic technique for surgery.

A left 4th intercostal thoracotomy is performed to access the PDA. After incision of the skin and the latissimus dorsi caudal to the scapula, the 4th intercostal space is identified.

The serratus ventralis and scalenus muscles are dissected and separated. The intercostal muscles are incised and the pleura space entered. The left cranial lung lobe is retracted caudally with sponges. A Finochietto retractor is used to retract the ribs. The vagus and the phrenic nerves are identified. The patent ductus arteriosus is located medially to the vagus nerve.

The dissection of the PDA is performed with a right-angled forceps. The dissection starts with the caudal part of the ductus. The cranial part is then dissected with the rightangled forceps. Sharp dissection with Metzembaum scissors is required to detach the pericardium from the ascending aorta. The right-angled forceps is dissecting between the ascending aorta, the pulmonary artery and the ductus. The forceps should be directed

caudally with a 45 degree angle to avoid the major blood vessels. After dissection of the PDA, 2 silk sutures are placed around the ductus. The suture the closest to the aorta is tied first.

Rupture of the PDA could happen during the dissection of the medial wall or ligation of the ductus. Small ruptures can be controlled by tamponnade. Bleeding may worsen with further dissection is attempted. More severe bleeding requires clamping of the ductus on each side of the tear. Mattress sutures with Teflon pledgets can then be placed across the ductus to control the hemorrhage. The ductus can be divided first then closed with mattress sutures. Both stumps of the ductus are oversewn with a simple continuous.

Prior to closure of the thoracic cavity a thoracostomy drain is placed. The thoracic cavity is closed in a routine fashion. Ribs are approximated with simple interrupted suture. The serratus ventralis muscle and scalenous muscles are closed with a simple continuous suture pattern (3-0 monofilament absorbable suture). The latissimus dorsi muscle is closed with a simple continuous pattern with 3-0 monofilament absorbable suture. The subcutaneous tissue is closed with a simple continuous suture pattern with a 3-0 braided absorbable suture. Skin is closed with a simple continuous suture pattern with 4-0 nylon.

The chest drain is maintained for 24 hours after surgery. If the thoracic cavity does not produce any fluid or air after 4 hours the drain might be removed then. The animals are maintained under fentanyl for 24 hours (2 to microgm/kg/hr IV).

Surgical technique fo occlusion Interventional cardiology is now commonly used to successfully occlude the PDA. With vascular access either through the femoral artery or vein a occlusion device is delivered in the PDA under visualization with fluoroscopy.

Dogs and cats with a PDA successfully ligated have an excellent long term outcome.

Even if mitral valve is present at the time of surgery it is not affecting the long term prognosis more likely because the mitral regain competency after reverse remodeling of the left ventricle after surgery.

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