TECHNICIAN UPDATE
Tachycardia Under Anesthesia— A Reaction to Potassium G Penicillin Joyce Guthrie, RVT On June 3, 2019, Barbie, a 15-month-old Quarter Horse mare was referred to the University of Missouri Veterinary Health Center, (MU-VHC), with a history of an unresolved colic. The mare had a history of colic approximately 2 months prior, which had been treated and resolved on the farm by the referring veterinarian with the nonsteroidal anti-inflammatory, flunuxin meglamine and hand walking. The current episode began on June 1, 2019 with signs of inappetence and rolling on the ground indicative of abdominal pain. As with the prior episode, Barbie had been treated by the referring veterinarian using flunixin meglumine and hand walking. Although there was some improvement and restoration of appetite, further signs of abdominal pain (including rolling on the ground) were evident by the next day. The mare was further treated with IV fluids and flunixin meglumine. Additional diagnostic tests undertaken by the referring veterinarian on the morning of June 3 included abdominocentesis, complete blood count (CBC) and abdominal ultrasonography. The peritoneal fluid appeared clear and yellow, a normal finding. Identified abnormalities included mild leukocytosis and abnormal small intestine. The mare was subsequently referred to MU-VHC for emergency treatment of colic. Upon arrival at MU-VHC, the mare exhibited ongoing signs of pain, and she tried to lie down and roll in the parking lot. The mare presented in adequate physical condition (BCS 4/9), weight 261 kg, rectal temperature 99.6° F (99.5° F–101.5° F), heart rate 64 bpm (28–44 bpm), respiratory rate 24 brpm (11–24 brpm). Ongoing signs of abdominal pain included continual attempts to collapse and roll. To facilitate further diagnostic testing, xylazine hydrochloride was administered on an as-needed basis over the course of the next 90 minutes. The mare’s mucous membranes were dark pink and moist, but the capillary refill time was <2 sec (a normal finding). Other abnormalities noted on physical examination included decreased borborygmi throughout all 4 quadrants and the presence of tympany in the dorsal aspect of the right flank. Following aseptic catheter placement in the left jugular vein, additional diagnostic tests included routine bloodwork (CBC, plasma biochemical profile, blood lactate and serum amyloid-A [SAA] concentra16
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tions), per rectum-abdominal palpation, passage of a nasogastric tube (for evaluation of reflux), and abdominal ultrasonography. Significant findings included absence of reflux, cloudy appearance to peritoneal fluid with neutrophilia 41,440/uL (<5,000/uL) 82% non-degenerated neutrophils and 18% macrophages, which sometimes displayed leukophagia. This was indicative of some degree of peritonitis and significant inflammation. Laboratory test results included an elevated SAA concentration (308 ug/mL, reference range <20 ug/mL) and normal lactate concentrations in both blood and peritoneal fluid. Ultrasonography revealed some dilated loops of small intestine in inappropriate locations, but with peristalsis present. There appeared to be a consolidated area of overlapping intestines or a small intestinal loop that was within the cecal lumen— this was not a repeatable finding—indicative of intussusception or severe inflammatory bowel disease. On abdominal palpation-per rectum, there was a small colon impaction that felt very hard and firm, and distended loops of small intestine. It was noted that the “impaction” was unusually hard and large. A foreign body was a potential differential diagnosis. Due to the intermittent colic, the age of the mare, peritoneal fluid analysis, findings on ultrasonography and abdominal palpation, the differentials were intussusception, small colon impaction—possibly a foreign body—and gastrointestinal disease leading to adhesions. were differential diagnosis. The findings were discussed with the owner, who agreed to an exploratory celiotomy.
Anesthesia
Barbie was walked to the anesthesia induction area where her mouth was rinsed and her feet cleaned. She was moved into the induction stall and sedated using xylazine hydrochloride 1.1 mg/kg (280 mg, IV). Following sedation, she was induced for general anesthesia with midazolam 0.033 mg/kg (8.5 mg, IV) and ketamine hydrochloride 2.5 mg/kg (700 mg, IV). The ketamine dosage was increased (normal dose 2.2 mg/ kg) due to a reduction in the midazolam dose (normal dose 0.066). Midazolam causes muscle relaxation with resultant respiratory depression. To avoid this effect, the midazolam dose was reduced by one-half. The mare was then intubated with a 22 mm endotracheal (ET) tube and mechanically lifted into the surgery suite where she was placed in dorsal recumbency. An ET tube cuff was inflated and used while the horse was connected to the anesthesia machine. For the first
