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Introduction by Ashutosh Wali, MD Advancements in Lung Isolation Techniques The Congenital Difficult Airway in Pediatrics Oxygen: Achieving a Rational Balance in Anesthetic Care Secrets of Flexible Fiber-Optic Intubation: Pearls for Success in Unusual Circumstances Supraglottic Airways as Bridges To Safe Extubation of the Difficult Airway

Surgical Management of the Failed Airway: A Guide to Percutaneous Cricothyroidotomy Topical and Regional Anesthesia for Tracheal Intubation The Video Laryngoscopy Market: Past, Present, and Future

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REFERENCE 1 4th National Audit Project of the Royal College of Anaesthetists and the Difﬁcult Airway Society: Major Complications of Airway Management in the United Kingdom. Report and ﬁndings: March 2011. Editors: Dr Tim Cook, Dr Nick Woodall and Dr Chris Frerk.

Introduction Airway Education and Training: Adapting to an Expanding Practice ASHUTOSH WALI, MD, FFARCSI Associate Professor of Anesthesiology Baylor College of Medicine Director, Advanced Airway Management Director, Division of Obstetric/Gynecologic Anesthesiology Ben Taub General Hospital Houston, Texas Dr. Wali is the 2014-2015 president of the Society for Airway Management.

he initial closed claims data analysis by the American Society of Anesthesiologists (ASA) Committee on Professional Liability found that 34% of all claims resulted from respiratory events and 85% of respiratory events were associated with permanent neurologic injury

or death.1 This report prompted the first guidelines by the ASA Task Force on Management of the Difficult Airway.2 The third iteration of the guidelines was published in 2013.3 However, airway management is not limited only to anesthesiologists. Airway management ubiquitously spans a wide range of the health care spectrum: prehospital settings, the emergency department, the operating room, endoscopy suites, the ICU, and hospital wards. Traditionally, basic methods of airway management were used to resolve airway issues in most of these clinical sites, with the exception of the operating room, where, if necessary, anesthesiologists would resort to devices and techniques of advanced airway management (AAM). As a result, anesthesiologists were increasingly asked to bring their AAM expertise to the other locations when needed. continued on page 4

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Over the past few years, the paradigm has shifted. The use of devices and techniques for AAM is being offered by local personnel in locations beyond the operating room. These providers include, but are not limited to, paramedics, emergency department physicians, intensivists, and pulmonologists. To keep up with the new and emerging devices and techniques for AAM, it is imperative to obtain and provide continuing airway education and training. For physicians, airway education and training should begin in medical school, expand during residency training, and continue enduringly into clinical practice. Models of airway education and training include the clinical arena, static simulation using manikins, dynamic simulation using simulators, the human cadaveric laboratory, and the animal laboratory. Each of these locations has its benefits and limitations. Ideally, a combination would be complementary, but the use of animal laboratories has declined dramatically in the past decade over concerns about the ethical treatment of animals. Many residency programs in the United States and Canada offer airway rotations to residents so they receive education and training in airway management. Typically, these rotations range from 1 week to 2 months.4-6 At Baylor College of Medicine (BCM), the PGY-2 anesthesiology residents undergo a 2-month advanced airway rotation. The first month is spent in obstetric and gynecologic anesthesia. Residents learn AAM devices and techniques, predominantly in patients with ASA physical status classifications of 2/3 who are under general anesthesia, unless awake intubation is warranted. The second month is spent in trauma anesthesia, where residents rotate in operating rooms for otorhinolaryngology, oromaxillofacial surgery, and trauma surgery. During this month, they gain more experience in awake intubation, mainly oral and nasal fiber optic, under topicalization and minimal sedation in predominantly ASA 3/4 patients. At both locations, airway devices and techniques are taught under the strict guidance and supervision of anesthesiology faculty. At the beginning of the AAM rotation at BCM, residents receive an orientation packet with goals, objectives, core competencies, a sample difficult airway letter, review articles—including the ASA difficult airway algorithm—and a minimal procedural checklist. The orientation packet and the difficult airway chart are discussed thoroughly with the residents and expectations are explained. The goals of the AAM rotation include familiarizing the residents with the ASA Practice Guidelines for the Difficult Airway, predictors of difficult intubation and difficult mask ventilation, and the design of various airway devices, as well as how to set up different airway devices and clean and sterilize basic airway equipment. The objectives of the rotation are to learn about proper positioning of the patient, adequate mask ventilation following induction of general anesthesia, proper use of the “BURP” maneuver and cricoid pressure, and appropriate use of airway devices such as standard laryngoscopes,

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the Eschmann stylet, video laryngoscopes, optical stylets, fiber-optic bronchoscopes, supraglottic airways, and airway exchange catheters. Finally, the residents visit the simulation laboratory as part of their simulation curriculum. They practice invasive airway access on manikins and are tested in real time on critical aspects of the ASA difficult airway algorithm, including awake tracheal intubation; the cannot-intubate, can-ventilate scenario; and the cannot-intubate, cannotventilate situation. Over the years, the AAM rotation has been extremely well liked by the residents and has consistently been rated in the top 1 to 3 rotations during the entire residency program. Continuing airway education and training is essential beyond residency training to maintain crucial airway skills, especially for emergency use. It is critical for airway managers to participate in conferences and workshops to stay updated with current airway literature on an ongoing basis. Recent literature from the United States and United Kingdom suggests that we have come close to mastering the difficult/failed tracheal intubation scenario thanks to the plethora of new airway devices that now are available. However, what also has become clear is that difficult emergence and difficult/failed tracheal extubation remain challenges for us to conquer.7,8 Opportunities abound for attending courses and meetings both nationally and internationally. The Society for Airway Management is a diverse group of physicians from specialties including anesthesiology, emergency medicine, intensive care, otorhinolaryngology, and pulmonology. The society fosters airway education, airway research, and airway-related clinical care. We conduct our annual scientific meeting and airway/simulation workshop every year in September. You are all invited to attend the 2014 conference September 19-21, in Seattle, Washington. Please refer to the website (www.samhq.com) for details.

References 1.

Caplan RA, Posner KL, Ward RJ, et al. Adverse respiratory events in anesthesia: a closed claims analysis. Anesthesiology. 1990;72(5):828-833.

2. Practice guidelines for management of the difficult airway. A report by the American Society of Anesthesiologists Task Force on Management of the Difficult Airway. Anesthesiology. 1993;78(3):597-602. 3. American Society of Anesthesiologists Task Force on Management of the Difficult Airway. Practice guidelines for management of the difficult airway: an updated report by the American Society of Anesthesiologists Task Force on Management of the Difficult Airway. Anesthesiology. 2013;118(2):251-270. 4. Hagberg CA, Greger J, Chelly JE, et al. Instruction of airway management skills during anesthesiology residency training. J Clin Anesth. 2003;15(2):149-153. 5. Dunn S, Connelly NR, Robbins L. Resident training in advanced airway management. J Clin Anesth. 2004;16(6):472-476. 6. Crosby E, Lane A. Innovations in anesthesia education: the development and implementation of a resident rotation for advanced airway management. Can J Anesth. 2009;56(12):939-959.

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Table of Contents 3

Introduction

Topical and Regional Anesthesia For Tracheal Intubation

Ashutosh Wali, MD

D. John Doyle, MD, PhD

Secrets of Flexible Fiber-Optic Intubation: Pearls for Success in Unusual Circumstances Katherine S. L. Gil, MD

Oxygen: Achieving a Rational Balance in Anesthetic Care Vincent J. Kopp, MD

The Video Laryngoscopy Market: Past, Present, and Future Kenneth Rothfield, MD

Advancements in Lung Isolation Techniques

Surgical Management of the Failed Airway: A Guide to Percutaneous Cricothyroidotomy

Wanda M. Popescu, MD

Joan E. Spiegel, MD, and Vipul Shah, MD

The Congenital Difficult Airway in Pediatrics

Supraglottic Airways As Bridges To Safe Extubation of the Difficult Airway

Cheryl K. Gooden, MD

Philip G. Schmid III, MD, and Mohammad El-Orbany, MD

Following page

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Topical and Regional Anesthesia For Tracheal Intubation D. JOHN DOYLE, MD, PHD Professor of Anesthesiology Staff Anesthesiologist Department of General Anesthesiology Cleveland Clinic Foundation Cleveland, Ohio Dr. Doyle reports no relevant financial conflicts of interest.

wake tracheal intubation commonly is used where ordinary

intubation—for example, attempting direct laryngoscopy following the induction of general anesthesia—is expected to be difficult or hazardous. Possible examples include patients with large glottic tumors, patients with unstable cervical spines, and patients known to be difficult to intubate from previous anesthetic misadventures.

Regardless of the reason that awake intubation is warranted, however, several underlying principles hold. The first is that whereas sedatives such as midazolam, fentanyl, and dexmedetomidine (Precedex, Hospira) undoubtedly are useful adjuncts to performing an awake intubation, the “secret recipe” is obtaining decent anesthesia to the airway structures; with good airway anesthesia, minimal or even no sedation is required, and patient cooperation is much easier to achieve.

The process begins by making some important airway management decisions, considered in Table 1. One important decision is whether to use needle-based airway blocks, described in Table 2. Table 3 lists some adjunctive drugs that may be useful and Table 4 details the steps for topicalization for awake intubation. This article also provides potentially useful clinical pearls and explains why clinicians may prefer to use lidocaine rather than benzocaine to obtain airway anesthesia.

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Table 1. Key Decisions When Planning Awake Intubation Oral versus nasal route: In patients with severe trismus, for example, a nasal approach generally is necessary. In addition, the surgeon sometimes will request nasal intubation to make the procedure go more smoothly. 2. Are needle-based local anesthetic blocks warranted? Two schools of thought exist: Use topical anesthesia exclusively, or employ needle-based airway blocks in addition to topical anesthesia (Table 2). The authorâ&#x20AC;&#x2122;s preference is the first approach. However, readers seeking more details on the use of needle-based airway blocks should consult the review by the New York School of Regional Anesthesia.1 3. Sedation protocol: Options include no sedation; midazolam, fentanyl, and propofol in various doses; dexmedetomidine; and other methods (Table 3). The author frequently administers 1 mg of midazolam, 50 mcg of fentanyl, and later 10 to 20 mg of propofol immediately before inserting the bronchoscope. 4. Should glycopyrrolate be given as an antisialogogue? 5. Which method of intubation? Options include fiber-optic intubation, video laryngoscopy, regular direct laryngoscopy, or another technique.

Table 2. Three Popular Airway Blocks for Awake Oral Intubation Where topical anesthesia is not desired or is proven to be ineffective, nerve blocks can be used. Needle blocks are at least relatively contraindicated in patients with coagulopathies or who are on anticoagulation. Always aspirate before injecting to ensure that the needle is not in a blood vessel. Potential complications of these blocks include bleeding, nerve injury, and seizures from intravascular injection. The following 3 upper airway blocks often are used: Glossopharyngeal Block The glossopharyngeal block numbs the oropharynx by anesthetizing the glossopharyngeal, or ninth cranial, nerveâ&#x20AC;&#x201D;a mixed nerve that provides sensation to the posterior third of the tongue, the vallecula, the anterior surface of the epiglottis (via the lingual branch), the tonsils (via the tonsillar branch), and the pharyngeal walls (via the pharyngeal branch). The glossopharyngeal nerve can be blocked by injecting approximately 5 mL of local anesthetic, such as 2% lidocaine, submucosally at the caudal aspect of the posterior tonsillar pillar where it crosses the palatoglossal arch. The block also can be achieved using direct mucosal application by pledgets soaked with local anesthetic, or even by spraying topical anesthesia onto the region. Some clinicians prefer to avoid needles for this block because it obviates the possibility of seizures triggered by accidental injection into the carotid artery. Finally, although a glossopharyngeal block facilitates intubation by blunting the gag reflex, it is not adequate as a solo technique. Superior Laryngeal Block The superior laryngeal block numbs the larynx above the cords. The internal branch of the superior laryngeal nerve originates lateral to the greater cornu of the hyoid bone and passes approximately 2 to 4 mm inferior to the greater cornu of the hyoid bone, where it pierces the thyrohyoid membrane to innervate the tongue base, the posterior surface of the epiglottis, the aryepiglottic folds, and the arytenoids. To perform this block, the patient is placed in a supine position with the head extended. The hyoid bone is identified, and a 25-gauge needle is advanced until it makes contact with the greater cornu of this structure on the side to be blocked. The needle is then walked off the bone inferiorly and advanced 2 to 3 mm. After a negative aspiration test, 2 to 3 mL of local anesthetic is injected, with an additional 1 to 2 mL administered as the needle is withdrawn. Similar to the glossopharyngeal block, the superior laryngeal block is inadequate as a solo technique. Translaryngeal Block The translaryngeal block numbs the larynx and trachea below the cords by anesthetizing the recurrent laryngeal nerve, which provides sensation to the trachea and vocal cords. To perform this block, a 5-mL syringe filled with 4% lidocaine and fitted with a 22- or 20-gauge IV catheter is advanced through the cricothyroid membrane until air is aspirated into the syringe. The needle is removed, leaving the IV catheter. Then 4 mL of 4% lidocaine is injected, inducing coughing, which scatters the local anesthetic.

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Clinical Pearls for Airway Anesthesia for Awake Intubation Topical anesthetics are available as a regular solution, a viscous solution, a gel, an ointment, or in a spray can. Topicalization is the easiest method for anesthetizing the airway; simply spray local anesthetic directly onto the airway mucosa. Nebulization of lidocaine 2% to 4% by oral nebulizer for 15 to 30 minutes also can be effective. Saliva acts as a barrier between the anesthetic agent and the mucosa; the administration of glycopyrrolate can help reduce the production of saliva. When gargling topical anesthetics such as 2% viscous lidocaine, most patients prefer to be sitting rather than supine. In addition, the patient can be encouraged to hold and control the Yankauer sucker to remove any excess anesthetic or to use after they have “had enough.” Cotton pledgets soaked in local anesthetic can be applied to targeted mucosal surfaces for 5 to 15 minutes to obtain selective blockade of underlying nerves. For nasal intubation, adding vasoconstrictors such as epinephrine at a concentration of 1:200,000, or phenylephrine at a concentration of 0.05%, to the local anesthetic solution can prolong the block and help reduce

mucosal bleeding. Needle-based airway blocks (Table 3) are far more complicated than noninvasive methods of providing anesthesia to the airway and generally are unnecessary to achieve good results. If the patient gags with the introduction of an airway guide (such as the Ovassapian or Williams airway), additional topicalization is needed. Performing elective fiber-optic intubation in routine cases in asleep patients will help the clinician master the use of the bronchoscope for intubation. Remember, however, that a jaw thrust from an assistant usually is needed to ensure that the scope passes easily. Remember that even if you see the tracheal rings through the fiber-optic bronchoscope, the endotracheal tube (ETT) may still occasionally end up in the esophagus, resulting in the patient coughing with attempted passage of the tube. Never put the patient to sleep until the capnogram waveform is what you expect! Passage of the ETT into the trachea can be complicated by the tube getting caught on the glottic structures. If this happens—indicated by the tube not passing easily—resolve the situation by rotating the ETT 180 degrees.

Table 3. Commonly Used Adjunctive Medications for Awake Intubation in Adults Medication

Dosage, Route, and Timinga

Action

Reversal Agent

Glycopyrrolate

0.2-0.4 mg IV or IM given 15-30 min preprocedure

Antisialogogue

None

Midazolam

0.5-4 mg IV (titrated to effect)

Sedative

Flumazenil

Fentanyl

25-100 mcg IV (titrated to effect)

Sedative

Naloxone

Remifentanil

Loading dose: 0.75 mcg/kg Infusion rate: 0.075 mcg/kg/minb

Sedative

Naloxone

Dexmedetomidine

Loading dose: 1 mcg/kg/h over 10 min Infusion: 0.7 mcg/kg/hc

Sedative

None

IM, intramuscular a

These are guidelines only; lower doses may be appropriate for frail patients and higher doses may be appropriate for other patients.

From reference 2.

From the manufacturer.

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Table 4. Key Steps in Performing Airway Anesthesia for Awake Intubation Step 1 (preparation): clinical review, equipment check, explanation to patient and assistants, oxygen via nasal cannula, Yankauer suction, bronchoscope suction, apply patient monitors, check patient IV, possibly administer glycopyrrolate, possibly administer sedation. Step 2: Have patient gargle 2% viscous lidocaine (delivered in sitting position using a small disposable drinking cup) (Figure 1). Step 3: Power spray 4% lidocaine to oropharyngeal and glottic structures (Figure 2). Step 4: Insert airway guide (if fiber-optic intubation is planned) (Figure 3). Step 5: Administer more 4% lidocaine through the airway guide using the MADgic Laryngo-Tracheal Mucosal Atomization Device (Figure 4). Step 6: Conduct immediate preintubation review: tracheal tube taped to the fiber-optic scope, scope suction working, image quality check, supply of propofol attached to the IV line. Step 7: Insert the fiber-optic scope, identify the epiglottis and the vocal cords, pass the bronchoscope past the cords, identify the carina, pass the tracheal tube, connect the patient breathing circuit, check for correct tracheal tube positioning clinically and by capnography. Step 8: Induce anesthesia (both IV and inhalational methods can be used). (Note that although the discussion here applies to the use of a fiber-optic bronchoscope, the use of a video laryngoscope also is possible [Figure 5]).

Figure 1. Viscous lidocaine 2% (Roxane Laboratories) can be given using a small disposable drinking cup.

Figure 2.

An oxygen-driven power sprayer can be used to deliver lidocaine to oropharyngeal and glottic structures. Oxygen at 15 Lpm is used (EZ-Spray, Intertex Research).

Figure 4.

The LMA MADgic Laryngo-Tracheal Mucosal Atomization Device (Teleflex) can be useful to assist in the delivery of topical anesthesia to the periglottic structures.

Figure 5.

A video laryngoscope such as the GlideScope (Verathon Medical) sometimes is used for awake intubation.

Figure 3. Airway guides can be useful to facilitate passage of the bronchoscope. Left to right: Berman, Williams, and Ovassapian airways. Courtesy of www.airwaycam.com.

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The Trouble With Benzocaine Administration of benzocaine is sometimes complicated by methemoglobinemia, the presence of elevated methemoglobin levels within circulating erythrocytes. Methemoglobin, being darkly pigmented, causes blood to appear chocolate-colored and the patient to look cyanotic. Dark arterial blood and cyanosis disproportionate to the extent of respiratory distress is suggestive of methemoglobinemia, which incidentally can be caused by factors besides benzocaine administration, including the antimalarial drugs chloroquine and primaquine, nitrites, nitrates, inhaled nitric oxide, and nitroprusside. As an example, Sachdeva et al3 describe a case of a man who underwent transesophageal echocardiography for evaluation of endocarditis and topical 20% benzocaine spray was administered for oropharyngeal anesthesia. Before topicalization, the patientâ&#x20AC;&#x2122;s oxygen saturation by pulse oximetry was 97% on room air, but following the administration of benzocaine spray, it fell to 80% despite oxygen administration. Clinically, the patient was cyanotic. Methemoglobinemia was suspected, and arterial blood gas evaluation by CO oximetry (with the patient on 6 L oxygen via nasal cannula) revealed the following: pH, 7.42; PO2, 248; PCO2, 34; oxygen saturation, 99%; and methemoglobin, 41.8% of total hemoglobin. After treatment with IV methylene blue at a dose of 2 mg/kg, cyanosis resolved, and a repeat methemoglobin level 2 hours later was 2.8%. Abdel-Aziz et al similarly described methemoglobinemia with the use of benzocaine spray for awake

fiber-optic intubation.4 Ferraro-Borgida et al described methemoglobinemia in a 34-year-old woman after perineal application of an over-the-counter cream containing 20% benzocaine.5 Finally, clinicians and parents will be interested to know that benzocaine is the active ingredient in many over-the-counter teething pain gels and liquid medications; for the reasons discussed, the FDA advises against the use of such products in children under age 2 years.6

References 1.

New York School of Regional Anesthesia. www.nysora.com/ techniques/nerve-stimulator-and-surface-based-ra-techniques/ head-and-neck-blocks/3022-regional-topical-anesthesia-forendotracheal-intubation.html. (Note that dexmedetomidine dose in the article is incorrect. It should be loading dose: 1 mcg/kg over 10 min, infusion rate: 0.2-0.7 mcg/kg per hour.)

2. Cattano D, Lam NC, Ferrario L, et al. Dexmedetomidine versus remifentanil for sedation during awake fiberoptic intubation. Anesthesiol Res Pract. 2012;2012:753107. 3. Sachdeva R, Pugeda JG, Casale LR, et al. Benzocaine-induced methemoglobinemia: a potentially fatal complication of transesophageal echocardiography. Tex Heart Inst J. 2003;30(4):308-310. 4. Abdel-Aziz S, Hashmi N, Khan S, et al. Methemoglobinemia with the use of benzocaine spray for awake fiberoptic intubation. Middle East J Anesthesiol. 2013;22(3):337-340. 5. Ferraro-Borgida MJ, Mulhern SA, DeMeo MO, et al. Methemoglobinemia from perineal application of an anesthetic cream. Ann Emerg Med. 1996;27:785-788. 6. So TY, Farrington E. Topical benzocaine-induced methemoglobinemia in the pediatric population. J Pediatr Health Care. 2008;22(6):335-359.

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Secrets of Flexible Fiber-Optic Intubation Pearls for Success in Unusual Circumstances

KATHERINE S. L. GIL, MD Associate Professor of Anesthesiology & Neurological Surgery Northwestern University Feinberg School of Medicine Chicago, Illinois Dr. Gil is editor of The Airway Gazette. She reports no relevant financial conflicts of interest.

othing is more satisfying than

the successful application of one’s inherent knowledge to

unusual patient circumstances, while staying out of trouble and avoiding court appearances. Anesthesiology, intensive care, and emergency department personnel know that the key to “being all that you can be” is practice and the ability to adapt.

Airway management caregivers value being expert in the use of a bare minimum of alternative airway devices, including flexible fiber-optic bronchoscopes (fiberscopes), also known as flexible endoscopes, employing video chips. This article offers fiber-optic pearls beyond straightforward intubation while promoting management comfort and protecting the equipment. For example, the use of fiber-optic devices provides several benefits to patients during tracheostomies: locating the trachea for surgical assistance, reducing the incidence of tracheostomy complications, and treating adverse results of tracheostomies. Transillumination of the fiber-optic light from within the trachea provides assistance in locating its anterior rings (the tip of the fiberscope is placed beyond the distal end of a preexisting airway). Surgeons will see a glow at skin level or during deeper tissue dissection (Figure 1). It might seem implausible that a surgeon cannot locate the trachea, but it does happen. I once had an extremely large, morbidly obese patient who presented

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for elective open tracheostomy. The surgery was to provide relief for his diagnosis of malignant sleep apnea, which had been resistant to all other forms of therapy. In anticipation of an awake fiber-optic intubation (FOI), we performed bilateral glossopharyngeal nerve blocks (2 mL of 3% lidocaine atomizer spray per side), bilateral percutaneous superior laryngeal nerve blocks (3 mL of 1% lidocaine), and a transtracheal injection of 4% lidocaine. FOI went smoothly. Unfortunately, even with easily seen transillumination, the surgical team could not find the trachea after 3 hours. (The team leader said the transtracheal injection was impossible, although the patient had coughed while it was being administered.)

TECHNIQUE In intubated patients or those receiving a supraglottic airway (SGA), the fiberscope can be inserted with the aid of an in-line fiberscope swivel adapter to permit continued ventilation (Figure 2). To prevent impaired ventilation and hypercarbia from potentially excessive â&#x20AC;&#x153;intra-airwayâ&#x20AC;? fiberscope bulk, the relationship between the diameter of the fiberscope and that of the secured preexisting or intended airway device must be carefully selected (Figure 3).1 This step is especially important if the patient has a condition highly sensitive to this possibility, such as increased intracranial pressure. If desired, a preemptive spray of intratracheal lidocaine through the suction or working port of the fiberscope reduces reaction to intratracheal stimuli from either extension of the fiberscope tip or surgical manipulations. The fiberscope is situated within the secured airway device until its tip lies beyond the end of the

Figure 1.

Transilluminated fiberscope tip within trachea.

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device, at least 2 to 3 cm below the second tracheal ring, according to the surgical teamâ&#x20AC;&#x2122;s intended incision site. It should be safeguarded in this position and powered on intermittently as needed for transillumination. Once the surgical team has physically located the trachea, the fiberscope should be protected by withdrawal as much as possible, while still allowing visualization of the impending surgical entry. If the preexisting airway is an endotracheal tube (ETT), the fiberscope is withdrawn immediately proximal to the tip of the ETT. (Note that a light wand also can provide transillumination, but does not have benefits associated with fiberoptic visualization.2) Anterior midline neck pressure on the proposed access point into the trachea often can be perceived by the caregiver, who is observing the fiberscope image. Once the surgical instrument is seen entering into the trachea, this action is reported to the surgeons and the fiberscope and ETT can be partially withdrawn 1 to 2 cm. Winkler et al found that of 71 patients undergoing percutaneous dilation tracheostomy (PDT) in the ICU, 18% had paramedian punctures that were corrected to midline after fiberscope guidance.3 Similarly, false passages from the tracheostomy tools are unlikely during fiberscope assistance. Whether blade incision for open tracheostomy or needling for PDT, direct observation of tracheal impact is associated with fewer serious surgical complications. In a study of 76 patients undergoing PDT with or without use of a fiberscope, Berrouschot et al found an equivalent rate of perioperative complications among patients treated with a fiberscope (7%) and those in the nonfiberscope group (6%).4 More severe complications,

Figure 2. adapter.

Fiberscope through in-line swivel

however, were significantly less frequent in the fiberscope group (2.5%) than in the non-fiberscope group (8%). These included perforation of the pars membranacea or posterior tracheal wall (3), intratracheal hemorrhage (3), tension pneumothorax (2), mediastinal emphysema (1), and death (1). One patient in the fiberscope group experienced a laceration and 2 experienced intratracheal hemorrhages. As the Berrouschot et al study demonstrated, a fiberscope on occasion can be used to treat tracheostomy complications: Two of the patients who experienced fiberscope-observed intratracheal hemorrhage were treated with fiberscope flushing and aspiration of the accumulated blood. The lower rate of severe complications associated with FOI has been shown to lower costs. Carillo et al reported a reduction in costs of $1,750 in PDT under fiberscope guidance compared with surgical tracheostomy.5 Use of a fiberscope can be economical in other scenarios as well, such as determining the position of an ETT and to prevent complications from intubations that are too shallow or too deep. Clinicians have a definite need beyond clinical signs and counting off ETT distance marks for determining the position of the tube. This need is particularly acute in longer-term intubation patients, as many studies have noted. In small children, diagnosing ETT position is particularly important because it is far from accurately assessed with these parameters. Malposition occurs frequently. Harris et al found that despite normal clinical signs in 257 children ages 6 months to 12 years, up to 18% had errantly placed ETTs.6 In children under 1 year of age, the incidence was 35%. Although 95% of patients had successful ETT repositioning after a single

chest x-ray, the other 5% needed readjustment during continuous fluoroscopy. The question arises, “Is there some other method that is just as effective?” and the answer is “Yes!” Vigneswaran compared the accuracy of a fiberscope and chest x-ray in 20 high-risk premature and full-term infants.6,7 Surprisingly, infants undergoing x-ray were more likely to experience large drops in oxygen saturation during the radiographs. This effect was thought to result from alterations in the position of the head and ETT. On the other hand, the group observed with fiberscopes—a subset of patients with secretions—experienced higher airway pressures and likely increased work of breathing, and significant but lower drops in oxygenation. The one advantage in this subset of patients was the ability to suction with the fiberscope. A comparison study between fiberscope and x-ray detection by O’Brien et al involving 25 adults also found equal accuracy in determining the distance of the ETT from the carina and laryngeal areas.8 Fiberscope examination is similar in cost to chest x-ray and considerably less than fluoroscopy. Use of a fiberscope also has the benefit of avoiding radiation. Although a single chest x-ray only incurs approximately 6 mrem, repeated x-rays or fluoroscopy may result in many times this degree of exposure. A fiberscope may be more advantageous than x-ray if urgency is a factor, as the fiber-optic examination can provide instantaneous results and can be used multiple times if circumstances dictate. In the event that a particular technique is unavailable or its use is technically problematic for determining distances, the opposite approach should be chosen.

Figure 3.

The “transillumination-assisted technique” permits greater passage of ventilation (red arrows) when less fiberscope bulk occupies the airway, as shown in frames A and B, in contrast to C and D.

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TECHNIQUE In infants, the tip of the ETT should be at least 2 cm above the carina, but no more than an additional 1.5 to 2 cm margin above that mark. In adults, the ETT tip generally should be at least 4 cm, and up to an additional 6 to 10 cm above the carina (Figure 4). Because of variations in sex, age, height, race, and other factors, these distances are not absolute, and other possible causes of malposition should be considered. Another advantage of this type of examination is gaining experience in fiberscope practice; a fiberscope also can be selected for examining patients with increased airway pressures, unexplained drops in oxygen saturation, secretions, and poor positioning of an SGA. In the pediatric population, as with adults, successful FOI often hinges on the availability and functionality of equipment. For a small patient, when the only available fiberscope is too large, all is not lost. This fiberscope can still complete intubation by serving as a means of inserting a long guidewire into the trachea. To accomplish wire delivery, the fiberscope must have a suction or working channel (Figure 5). Any flexible Teflon-coated guidewire can be used if its specifications correspond to the dimensions of the fiberscope channel (usually 0.032-0.038 inch [0.81-0.97 cm] in diameter) and it is at least 20 cm longer than the scope (usually 110-150 cm).

TECHNIQUE The wire should be extended 0.5 to 1.0 cm out of the tip of the fiberscope. The end protruding from the working port can be taped to the handle. In asleep or awake (topically anesthetized) patients, the wireloaded fiberscope is then inserted to view the glottis. At this point, the airway operator gives an assistant a previously arranged signal to free the wire and slowly advance it. Meanwhile, the operator manipulates

Figure 4.

Endotracheal tube distance to carina measured by fiberscope.

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the fiberscope control to ensure its correct passage between the vocal cords. The wire should be inserted until resistance in the distal tracheal is felt; the distance from the vocal cord to carina averages 4 to 9 cm in pediatric patients and 10 to 15 cm in adults. The fiberscope is carefully withdrawn while preventing outward movement of the wire. If desired, once the solitary wire remains in the patient, ordinary facemask ventilation can be administered by bending the wire over until the next step. At this point, if the diameter of the wire and the inside of the ETT are similar, it might be possible to railroad the ETT over the wire into the trachea. During FOI, however, advancement of an ETT through the glottis can be problematic if the diameters do not match. Hakala et al studied 2 groups of 40 adults undergoing FOI with a fiberscope of either 3.7 or 5 mm diameter.9 They found that resistance to ETT passage was 35% with a thinner fiberscope and 11% with a larger one. The failure rate was 20% among patients treated with the thinner scope, and zero for the others. This difficulty is thought to result from periglottic hang-up of the ETT, most frequently after posterior misdirection of the ETT into the esophagus, or ETT impingement on the arytenoids, particularly on the right. The same situation presumably can arise if there is discordance between the diameters of the guidewire and ETT. To forestall this possibility, vascular, cardiac, or Cook airway exchange catheters (AECs) can be introduced over the wire to more closely approximate diameters. The ETT should be pretested to assure its fit over the catheter, and likewise, that the catheter fits over the wire.

ALTERNATIVE TECHNIQUE A wire-stylet epidural catheter can substitute for a guidewire (similar to retrograde intubation use), but may be less preferable due to comparably greater epidural catheter flexibility. A â&#x20AC;&#x153;too-largeâ&#x20AC;? fiberscope can

Figure 5. channel.

Wire extending from working

be useful if the patient requires FOI but the only available pediatric fiberscope is ultrathin and lacks a working channel for the administration of local anesthetic to prevent laryngospasm.

TECHNIQUE The larger fiberscope is inserted for laryngoscopy and, after visualizing the glottis, local anesthesia is sprayed through the working channel onto the vocal cords. Seconds later, following the onset of local anesthesia after removing the fiberscope, FOI is performed with the ultrathin device. Can use of a fiberscope eliminate blind airway management methods, such as blind nasal intubation, ETT exchanges, and insertions of SGAs? Perhaps it is a little radical to advocate fiberscope deployment to eliminate these airway techniques because they often are simple, effective, and cheap. Rather than taking on all the worldwide airway practitioners who advocate these methods, here are some alternatives for circumstances where risks can be reduced, success rates can definitely be improved, and a fiberscope can rescue blind ventures.

Eliminating Blind Nasal Intubation Any patient with prohibitive anatomy for oral intubation, and nasal passages too small to admit an ETT over a fiberscope, may still require nasotracheal intubation (Figure 6). A blind nasal intubation might be deleterious considering trauma and edema from the unseen ETT tip.

TECHNIQUE In this situation, a smaller ETT plus a side-by-side fiberscope technique can be employed (Figure 7). After administration of topical medication including

Figure 6.

Interdental distance = 0 mm.

vasoconstrictors, an appropriately sized, lubricated ETT is inserted into one nasopharyngeal passage. A fiberscope is advanced through the other passage until the vocal cords appear at a distance far from the periglottic region. From this viewpoint, the operator can instruct an assistant to slowly feed the ETT forward until it enters between the vocal cords. If the tip of the ETT seems to be directed too posteriorly, the assistant can inflate the ETT cuff, pushing the tip off the posterior pharyngeal wall toward the glottis (Figure 8). The assistant can then slowly deflate the cuff while keeping the tip at the glottis for tracheal intubation until the signal to advance it is given. If the ETT goes astray (anteriorly, laterally, or posteriorly), other maneuvers are activated, including pressure on the thyroid cartilage, neck flexion, neck extension, or ETT rotation, during which time the assistant withdraws or advances the ETT as directed.

ALTERNATIVE TECHNIQUE Despite having no oral entry for airway devices due to severely abnormal anatomy, some patients have retromolar areas that allow a fiberscope to squeak through (Figure 9). This permits a modified â&#x20AC;&#x153;side-byside technique.â&#x20AC;? If large enough, it may even admit an ETT-loaded fiberscope for FOI.

Eliminating Blind ETT Exchanges Blind ETT exchanges often succeed with the insertion of a Cook AEC down the old ETT, followed by removal of the tube and attempts to railroad a new ETT over the catheter. However, during this process, the disaster of airway loss is quite possible. ETT exchange frequently involves a patient with a difficult airway or low tolerance for lost ventilation. Any preexisting ETT may have softened and bent in the

Figure 7.

Side-by-side technique.

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pharynx. A leaky cuff often is reinflated with more and more air over time, and the tip of the ETT may migrate upward into the periglottic area, away from the trachea. Blind insertion of a catheter in these situations does not guarantee it will end up in the correct location in the respiratory tract. McLean et al found a 13.8% incidence of failure of blind ETT exchange in an analysis of 1,177 patients.10 Pneumothorax occurred at a rate of 1.5%; of those, 75% occurred in cases of difficult exchange.

TECHNIQUE For adults, the blind technique can be changed to perhaps just having a small cataract. Gauze availability and testing of a pediatric fiberscope through a well-lubricated Aintree catheter (4.7 mm internal diameter) is mandatory. Similar to the AEC, ventilation via the Aintree is possible. Sedation helps prevent bucking. The old ETT must be at least 6.5 mm in diameter. The catheter-loaded fiberscope is inserted through the old ETT with the scope tip leading the way (Figure 10). Nonvisualization of the trachea may indicate extubation and the need for airway rescue. Otherwise, once the carina is seen, the Aintree is railroaded close to it. The fiberscope and ETT are removed while securing the catheter. A new ETT-loaded fiberscope is placed within the catheter until nearing the carina. The ETT is secured while removing the catheter and fiberscope.

Figure 8.

Effect of endotracheal tube cuff inflation during fiber-optic assisted nasotracheal intubation.

Figure 9.

Figure 10.

Fiberscope within an Aintree catheter, within an endotracheal tube.

Fiberscope entering deeply into retromolar space.

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Figure 11.

Fiberscope tip protected in bowl of supraglottic airway.

ALTERNATIVE TECHNIQUE

Figure 12.

Fiberscope tip extended beyond bowl of supraglottic airway.

A wire-loaded fiberscope is advanced through the old ETT. After leaving only the wire by the carina, a new ETTloaded fiberscope can be threaded over it to situate the ETT at an appropriate depth, after which fiberscope and wire are extracted.

the fiberscope can be extended out of the SGA while one assistant stabilizes the airway and another performs jaw thrust. Once periglottic structures have been identified, the SGA is railroaded over the fiberscope. After its positioning is visually inspected, the fiberscope is withdrawn.

Eliminating Difficult SGA Placement

ALTERNATIVE TECHNIQUE

This technique is particularly useful for anticipated problematic placement of an SGA. It can be performed in any asleep or awake patient. Preparation includes complementary SGA and fiberscope sizes and a welllubricated fiberscope (Figures 11 and 12).

Obviously, some of these approaches can be used for ETT intubation through the SGA if there is an interest in eliminating the blind part of an intubating laryngeal mask airway (LMA Fastrach, Teleflex) or other trans-SGA intubation. The caveat is that the success rate of Fastrach intubation changes from 97% after 3 blind attempts to almost 100% with a fiberscope.11

TECHNIQUE Different approaches are possible. Prepared devices can be loaded to keep the fiberscope tip protected just prior to the exit point of the SGA and prevent outward movement of the fiberscope. An assistant opens the patient’s mouth widely and applies tongue pull and neck extension, if permissible. The SGA is inserted according to manufacturer’s recommendations. After initial mouth entry, fiberscopic observation is used to locate periglottic anatomy and the SGA is positioned. If the glottis is not found, the SGA can be pulled back a bit and

References 1.

2. 3.

5. 6.

Reilly PM, Sing RF, Giberson FA, et al. Hypercarbia during tracheostomy: a comparison of percutaneous endoscopic, percutaneous Doppler, and standard surgical tracheostomy. Intensive Care Med. 1997;23(8):859-864. Walls RM, Murphy MF. Manual of Emergency Airway Management. New York, NY: Lippincott Williams & Wilkins, 2008;151. Winkler WB, Karnik R, Seelmann O, et al. Bedside percutaneous dilational tracheostomy with endoscopic guidance: experience with 71 ICU patients. Intensive Care Med. 1994;20(7):476-479. Berrouschot J, Oeken J, Steiniger L, et al. Perioperative complications of percutaneous dilational tracheostomy. Laryngoscope. 1997;107(11):1538-1544. Carrillo EH, Spain DA, Bumpous JM, et al. Percutaneous dilational tracheostomy for airway control. Am J Surg. 1997;174(5):469-473. Harris EA, Arheart KL, Penning DH. ETT malposition within the pediatric population: a common event despite clinical evidence of correct placement. Can J Anesth. 2008;55(10):685-690.

Conclusion Each of the many devices for airway management requires practice to enable ease of use. When recalling the early months of residency, the common laryngoscope was perhaps the hardest to master. With determination, expertise with a flexible fiberscope is readily attainable. Once the barrier of apprehension is eliminated, the elation from success in difficult situations—when it really makes a difference to the patient—is extraordinary. 7. Vigneswaran, R. The use of a new ultra-thin fiberoptic bronchoscope to determine ETT position in the sick newborn infant. Chest. 1981;80(2):174-177. 8. O’Brien D, Curran J, Conroy J, et al. Fibre-optic assessment of tracheal tube position. A comparison of tracheal tube position as estimated by fibre-optic bronchoscopy and by chest X-ray. Anaesthesia. 1985;40:(1)73-76. 9. Hakala P, Randell T. Comparison between two fibrescopes with different diameter insertion cords for fibreoptic intubation. Anaesthesia. 1995;50(8):735-737. 10. McLean SI, Lanam CR, Benedict W, et al. Airway exchange failure and complications with the use of the Cook Airway Exchange Catheter: a single center cohort study of 1177 patients. Anesth Analg. 2013;117(6):1325-1327. 11. Ferson DZ, Rosenblatt WH, et al. Use of the intubating LMAFastrach in 254 patients with difficult-to-manage airways. Anesthesiology. 2001;95(5):1175-81.

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Oxygen: Achieving a Rational Balance in Anesthetic Care VINCENT J. KOPP, MD

Professor of Anesthesiology and Pediatrics Department of Anesthesiology School of Medicine University of North Carolina at Cha apel Hill Chapel Hill, North Carolina Dr. Kopp reports no relevant financial conflicts of interest.

umans have evolved to thrive at or near 21% inspired oxygen

(FiO2 = 0.21). After achieving a patent airway during anesthesia, clinicians face 3 interrelated concerns regarding oxygen:

delivery, utilization, and toxicity. Although delivery and utilization are met, toxicity is discounted. As with too little oxygen, too much is consequential. Toxicity in either case is dramatic, subtle, or delayed.1-3

Contemporary medicine’s “culture of oxygen” 4 assumes oxygen is always safe. This assumption is undeserved. Ingrained practice habits, pulse oximetry and the misinterpretation of blood gas data, and unfamiliarity with basic oxygen science contribute to the problem.5-9 On the positive side, new guidelines incorporate sound knowledge about oxygen toxicity into strategies to guarantee the use and delivery of oxygen while minimizing risk for harm from the gas.10-12 This article considers toxicity in relation to delivery and utilization as an omnipresent risk, especially in anesthesia care.13-15 The take-away message is simple:

The best “antioxidant” is restricted use of oxygen. When a “lowest oxygen level acceptable” (LOLA) standard is matched to clinical need and adjusted using data, the toxicity of oxygen can be reduced, but never eliminated.

Oxygen Delivery Guaranteeing oxygen delivery requires a patent airway. Open passages permit oxygen; carbon dioxide; nitrogen; water vapor; and other inhaled, exhaled, or metabolically generated gases to move along separate partial pressure gradients toward equilibrium. Ventilation opens airways and alveoli so bidirectional gas flow is unimpeded. Alveolar–capillary gas exchange

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reflects maintenance of an adequate partial pressure gradient. Respiration requires oxygen to make adenosine triphosphate (ATP). Carbon dioxide and water are byproducts. Mitochondria make 90% of cellular ATP, which number in the billions, via oxidative phosphorylation.16 Supplying mitochondria with enough oxygen to respire requires reliable delivery. Most anesthesia providers learn that oxygen delivery (DO2) equals cardiac output (CO) multiplied by arterial oxygen content (CaO2): DO2 = CO x CaO2.17 Factors ignored in this equation deserve review. As a global measure, DO2 is insensitive to local conditions. Organs behave individually. Vascular responsiveness is not uniform. Changes in oxygen tension affect delivery efficiency. Oxygen delivered directly to tissue bypasses circulatory delivery. Excessive direct oxygen exposure also promotes tissue injury. In addition to the lungs, gas-containing compartments, such as respiratory sinuses and gastrointestinal segments, experience direct-contact delivery and use. Theoretically, microbiome delivery produces metagenomic effects that might affect local delivery.18,19 Parsing DO2 is instructive. Cardiac output equals heart rate (HR) multiplied by stroke volume (SV): CO = HR x SV. It also equals mean arterial pressure (MAP) minus central venous pressure (CVP) divided by systemic vascular resistance (SVR): CO = MAP – CVP/SVR. Because both of these expressions equal CO, they equal each other: CO = HR x SV = MAP – CVP/SVR. CaO2 is more complex. Arterial hemoglobin concentration ([Hb] g/dL) multiplied by arterial oxygen saturation (SaO2 %/100) multiplied by oxygen volume bound

to normal Hb in a volume of blood (1.39 mL/g), added to the product of the oxygen solubility coefficient (0.003 mL O2/100 mL plasma/mm Hg) times the arterial oxygen partial pressure (PaO2 mm Hg) equals CaO2. For clinicians, this DO2 formula offers 7 factors to manipulate: Hb, PaO2, HR, SV, MAP, CVP, and SVR. This array may account for its popularity. Functional magnetic resonance imaging studies show that increasing FiO2 to 1 increases tissue oxygen partial pressure (PtO2) significantly in rat brain, kidney, liver, gut, muscle, and skin.20 It is no wonder that increasing FiO2 when SaO2 falls is a default maneuver to increase PaO2 and PtO2. The effect, however, produces a submolecular cost.

Use of Oxygen The use and delivery of oxygen are metabolically linked by sensing mechanisms that are not completely understood.21 Normal perfusion is regulated by local oxygen use in all organs except the kidneys.21 This linkage means the influence of CO on oxygen delivery has limitations. Indeed, at low CO, the need to increase FiO2 to enhance DO2 is considered axiomatic. In the absence of significant hypoxemia, however, this intervention may not always be necessary or desirable. More research needs to be conducted to define relevant parameters. Sensing mechanisms for the regulation of oxygen depend on local states of mitochondrial energy, substrate availability, levels of reactive oxygen species (ROS), antioxidant/prooxidant balances, calcium and other ion flux controls, maintenance of inner membrane/matrix electrochemical gradients, the functional states of mitochondrial transmembrane potential and

Figure Key

Pyruvate PDH Acetyl CoA

PDKI

ADP, adenosine diphosphate ATP, adenosine triphosphate CoQ, coenzyme Q10

TCA Cycle Mito Matrix

FADH2 FAD+ O2

+ O2 NADH NAD

II I

CoQ

1/2 O2

H2O ADP+Pi ATP

O2 III

FoF1 ATPase

H+

CytC H+

H+

IMM

Oxygen use by the respiratory chain—oxygen accepts electrons at Complex IV to make ATP.

I N D E P E N D E N T LY D E V E L O P E D B Y M C M A H O N P U B L I S H I N G

NAD+, nicotinamide adenine dinucleotide, oxidized

OMM, outer mitochondrial membrane

Cytosol

Figure courtesy of Dr. Gregg Semenza.

IMM, inner mitochondrial membrane

NADH, nicotinamide adenine dinucleotide, reduced

OMM

Figure 1.

FAD, flavin adenine dinucleotide

PDH, pyruvate dehydrogenase PDKI, phosphoinositide-dependent kinases ROS, reactive oxygen species TCA, tricarboxylic acid

transition pore, and the injury status of mitochondrial DNA.23 Hypoxia-inducible factor plays a pivotal role in cellular responses to both hypoxia and hyperoxia.24 That eukaryotic cells adjust readily to shifting oxygen levels within a narrow range is key to life and health.24 More than 200 cellular reactions use oxygen. Although oxygen is the main biological oxidant to an array of reductants, it also builds molecules and regulates multiple non–respiratory chain functions.17,26 Ultimately, all use of oxygen reflects PtO2, which in turn determines the partial pressure of mitochondrial oxygen (PmitO2).27,28 The minimum PmitO2 required to support metabolism is surprisingly low. The threshold above which the consumption of mitochondrial oxygen remains “supply independent” is 0.1 kPa or 0.75 mm Hg.29 Some lower estimates exist.30 As a result, PmitO2 above such values may not enhance mitochondrial function. Mitochondria consume 90% of all oxygen absorbed; non-mitochondrial use accounts for 10%. Of the 90% mitochondrial use, 80% is directly coupled to the synthesis of ATP, whereas 20% is uncoupled from production of the molecule. This process occurs through leakage of mitochondrial protons associated with free energy production, dissipation of heat, degradation of proteins, and the activity of sodium and calcium ion pumps.26 The 80% of oxygen use coupled to production of ATP occurs at Complex IV (cytochrome C oxidase). At this site, oxygen accepts respiratory chain electrons needed to drive Complex IV-mediated (ATPase) ATP synthesis from inorganic phosphorous and adenosine 5'-diphosphate binding. Simultaneously, the 4-electron transfer to O2 (dioxygen) pumps hydrogen ions from the mitochondrial intermembranous space back into the mitochondrial matrix. This action maintains the chemiosmotic gradient that supports the electrochemical balance in mitochondria that enables adequate respiratory chain function and mitochondrial integrity26 (Figure 1). Notably, the respiratory chain efficiency is not 100%. Approximately 1% to 2% of the 80% mitochondrial oxygen use aimed at ATP production fails to make ATP. Electron escape produces single electron oxygen reductions inside mitochondria, especially at Complexes I and III, sites also affected by anesthetics.31,32 The superoxide ions formed are converted to diffusible hydrogen peroxide by the antioxidant superoxide dismutase, of which a specialized mitochondrial version exists. Superoxide and hydrogen peroxide become intermediaries in complex cell signaling events. Other ROS, such as highly reactive but short-lived hydroxyl radicals, and reactive nitrogen species (RNS) also form against defenses that are less understood. These react in damaging ways with lipids, proteins, DNA, and transition metals such as ferrous iron, sulfur, and copper.33 Together, abnormal levels of ROS and RNS amplify oxygen toxicity in all tissues but especially neurons, glia, and myelin in the nervous system.34

Oxygen Toxicity Comroe and colleagues first systematically studied human oxygen toxicity in 1945. Subjects exposed to 100% oxygen at sea level for 24 hours and at a simulated altitude of 18,000 feet showed signs and symptoms of oxygen toxicity that included cough, sore throat, nasal congestion, eye irritation, ear and dental discomfort, substernal distress, decreased vital capacity, decreased gastrointestinal lumen size, atelectasis, “pulmonary irritation,” fatigue, joint pain, paraesthesias, myalgias, dizziness, lightheadedness, and variable changes in blood pressure, respiratory rate, and hematologic parameters.35 In their 1950 monograph, Comroe and Dripps catalogued more changes: nitrogen reduction, respiratory depression before respiratory stimulation, interference with elimination of carbon dioxide, circulatory depression, increased diastolic blood pressure, bradycardia, reduced CO, systemic arterial constriction, reduction in coronary blood flow, retinal artery constriction, depression of cerebral cortical function, changes in pulmonary blood flow, and suppression of bone marrow.36 In 1951, Weschler and colleagues showed for the first time that cerebral oxygen consumption was reduced during thiopental anesthesia.37 In 1954, Gerschman showed that toxicity from oxygen and radiation shared a mechanism, anticipating future research into ROS.38 By 1956, Kinsey showed retrolental fibroplasia to be unequivocally linked to the duration of exposure to oxygen—the first pediatric condition to be so linked.39 It took years of work by many scientists to discover oxidative stress, ROS, and the details of oxygen toxicity beneath clinically observed signs and symptoms. Oxygen toxicity occurs when intra-mitochondrial prooxidant/antioxidant factors are unbalanced (Figure 2). Excessive ROS overwhelm intra-mitochondrial antioxidants, which decline with age; chain reactions among ROS-susceptible structures promote cell death by triggering apoptosis and/or necrosis. Peroxidation of cardiolipin, abundant in the mitochondrial

m De

Excess ROS production

Homeostasis

PO2

ATP depletion, Excess ROS production

Figure 2.

Oxygen partial pressure (PO2) and reactive oxygen species (ROS) generation; harm from too little and too much oxygen share ROS as a mechanism. Figure courtesy of Dr. Gregg Semenza.

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inner membrane, is critical to apoptosis. Release of cytochrome C into the intermembranous space triggers a caspase cascade, which produces intrinsic apoptosis.7 Extrinsic apoptosis, triggered by mitochondrial outer membrane events, may be relevant to anesthesia in ways that are unexplored. Hyperoxia, which elevates PtO2 and PmitO2 above biologically necessary levels, feeds ROS-mediated chain reactions by mass action. Whereas anoxia– hyperoxia after ischemia–reperfusion pathologically swings PtO2 and PmitO2 to raise ROS concentrations inside injured mitochondria and cells, similar shifts exist when normally perfused uninjured cells are whipsawed between normoxic and hyperoxic conditions. Unfortunately, iatrogenically induced shifts in PO2 are common during routine anesthetic care. When the airway is patent and cellular oxygen use is reduced below unanesthetized levels, there is little rationale for routine oxygen supplementation above awake or baseline concentrations.

Clinical Implications Toxicity equals physiologic effects and submolecular events. Some are clinically apparent, like absorption atelectasis or arterial vasoconstriction; some are not, like lipid peroxidation and mitochondrial and nuclear DNA damage. Three clinical examples beyond the neonatology literature may suffice to illustrate that more oxygen is not always better or necessary. As proof grows that oxygen moderation is possible and desirable, skeptics remain. It is hard to break the oxygen habit and go against the prevailing culture. Oxygen cannot be stored in the lungs but breathing 100% oxygen (FiO2 = 1) can increase the time to “significant” desaturation, itself a slippery metric as PaO2 is more important, after breathing ceases. Preoxygenation and denitrogenation have been studied using blood gases and imaging studies since the 1940s into the 2000s, but not in relation to cellular events that might ensue even from brief hyperoxemic/ hyperoxic exposures. Oxidative stress biomarker studies relevant to clinical anesthesia practice remain to be done. Despite no biomarker evidence, Lindahl and others have advanced rational arguments for “dialing back oxygen” before, during, and after intubation and extubation, and during recovery. Clinicians need not wait to heed their data or advice. Another example where clinical hyperoxia has proven problematic is traumatic brain injury. Small but provocative studies looking at blood flow using positron emission tomography scans and patient outcomes have led to recommendations not to use 100% oxygen in such settings. Safe levels are not defined but maintaining normoxia is advisable. Furthermore, the combination of hyperoxemia and hyperventilation causing hypocarbia together reduces cerebral blood flow so that both mechanisms contribute to extension of ischemic region and penumbral damage.

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A third example where oxygen caution is advisable is in caring for patients with diseases linked to oxidative stress. These include autism spectrum disorder, Alzheimer’s disease, Parkinson’s disease, type 1 diabetes, cancer, and cardiovascular disease. Patients with these conditions frequently require surgery. Because they are already burdened with oxidative stress, hyperoxemia and hyperoxia impose an additional burden that may accelerate a disease process. That said, healthy individuals are also at risk for increased oxidative stress during surgery. Using the least amount of oxygen required to support homeostasis remains a rational caution.

Conclusion In the introduction, a LOLA standard was offered as a clinical “antioxidant” strategy. Like Martin and Grocott’s “precise control of arterial oxygenation” (PCOA) and “permissive hypoxaemia” (PH) concepts,40 a LOLA standard addresses a shared concern: hyperoxemia. Like PCOA and PH, LOLA calls for data-driven, scientifically sound use of oxygen. A significant challenge to LOLA exists, however: human nature. Pulse oximetry facilitates monitoring of SaO2; it also biases toward oversupplementation. At 100%, SaO2/PaO2 Hb-oxygen dissociation relationships can vary 6-fold (100-600 mm Hg). The tone drop with a decrease in SaO2 from 100% to 97% is disproportionate to its physiologic significance. The response might be to increase FiO2. With pulse oximeter chirps restored to 100%, the patient again risks being overdosed. Invisibly, ROS accumulate beyond need and intrinsic antioxidant capacity; invisibly, damage is undetected or misinterpreted at the postoperative check. Clinicians use supplemental oxygen to “guarantee” the delivery of the gas. But oxygen’s therapeutic window is not infinite. The value of a LOLA or PCOA standard is the awareness that overdosage of oxygen demands a solution. If safety is freedom from harm, one safety goal should be minimizing submolecular damage. This goal can be achieved even as science addresses any remaining questions.41

References 1.

de Jonge E, Peelen L, Keijzers PJ, et al. Association between administered oxygen, arterial partial oxygen pressure and mortality in mechanically ventilated intensive care unit patients. Crit Care. 2008;12(6):R156.

2. Diringer MN, Aiyagari V, Zazulia AR, et al. Effect of hyperoxia on cerebral metabolic rate for oxygen measured using positron emission tomography in patients with acute severe head injury. J Neurosurg. 2007;106(4):526-529. 3. Khaw KS, Wang CC, Ngan Kee WD, et al. Effects of high inspired oxygen fraction during elective Caesarean section under spinal anaesthesia on maternal and fetal oxygenation and lipid peroxidation. Br J Anaesth. 2002;88(1):18-23. 4. Leach RM, Davidson AC. Use of emergency oxygen in adults. BMJ. 2009;338:366-367. 5. Gordon RJ. Anesthesia dogmas and shibboleths: barriers to patient safety? Anesth Analg. 2012;114(3):694-699.

6. Pedersen T, Nicholson A, Hovhannisyan K, et al. Pulse oximetry for perioperative monitoring. Cochrane Database Syst Rev. 2014;3:CD002013. 7. Ott M, Gogvadze V, Orrenius S, et al. Mitochondria, oxidative stress and cell death. Apoptosis. 2007;12(5):913-922. 8. Martin LJ. Mitochondrial and cell death mechanisms in neurodegenerative diseases. Pharmaceuticals (Basel). 2010;3(4):839-915. 9. Semenza GL. Oxygen sensing, hypoxia-inducible factors, and disease pathophysiology. Annu Rev Path Mech Dis. 2014;9:47-71. 10. O’Driscoll BR, Howard LS, Davison AG. BTS guideline for emergency oxygen use in adults. Thorax. 2008;63(suppl 6):vi1-68. 11. 2010 American Heart Association guidelines for cardiopulmonary resuscitation and emergency cardiovascular care science. Circulation. 2010;122:S640-S656. 12. Resuscitation Council (UK). The resuscitation guidelines 2010. https://www.resus.org.uk/pages/guide.htm. Accessed July 15, 2014. 13. Iscoe S, Beasley R, Fisher JA. Supplementary oxygen for nonhypoxemic patients: O2 much of a good thing? Crit Care. 2011;15(3):305-308. 14. Meyhoff CS, Staehr AK, Rasmussen LS. Rational use of oxygen in medical disease and anesthesia. Curr Opin Anaesthesiol. 2012;25:363-370.

25. Semenza GL. Life with oxygen. Science. 2007;318(5847):62-64. 26. Rolfe DFS, Brown GC. Cellular energy utilization and molecular origin of standard metabolic rate in mammals. Physiol Rev. 1997; 77(3):731-758. 27. Mik EG. Special article: measuring mitochondrial oxygen tension: from basic principles to application in humans. Anesth Analg. 2013;117(4):843-846. 28. Vanderkooi JM, Erecinska M, Silver IA. Oxygen in mammalian tissue: methods of measurement and affinities of various reactions. Am J Physiol. 1991;260(6 Pt 1):C1131-C1150. 29. Kuper M, Soni NC. Oxygen transfer: cascade or whirlpool? Curr Anaesth Crit Care. 2003;14(2):58-65. 30. Honig CR, Connett RJ, Gayeski TEJ. O2 transport and its interaction with metabolism; a systems view of aerobic capacity. Med Sci Sports Exerc. 1992;24(1):47-53. 31. Kajimoto M, Atkinson DB, Ledee DR, et al. Propofol compared to isoflurane inhibits mitochondrial metabolism in immature swine cerebral cortex. J Cereb Blood Flow Metab. 2014;34(3):514-521. 32. Cella O, Piccoli C, Scrima R, et al. Bupivacaine uncouples the mitochondrial oxidative phosphorylation, inhibits respiratory chain complexes I and III and enhances ROS production: results of a study on cell cultures. Mitochondrion. 2010;10(5):487-496.

15. Decalmer S, O’Driscoll BR. Oxygen: friend or foe in peri-operative care? Anaesthesia. 2013;68(1):1-12.

33. Cadenas E, Davies KJA. Mitochondrial free radical generation, oxidative stress, and aging. Free Radic Biol Med. 2000;29(3-4):222-230.

16. Barbour JA, Turner N. Mitochondrial stress signaling promotes cellular adaptations. Int J Cell Biol. 2014;156020.

34. Smith KJ, Kapoor R, Felts PA. Demyelination: the role of reactive oxygen and nitrogen species. Brain Pathol. 1999;9(1):69-92.

17. Lumb AB. Nunn’s Applied Respiratory Physiology. 7th edition. Edinburgh, UK: Churchill Livingstone Elsevier. 2010:179-215. 18. Cho I, Blaser MJ. The Human microbiome: at the interface of health and disease. Nat Rev Genet. 2012;13(4):260-270.

35. Comroe JH, Dripps RD, Dumke PR, et al. Oxygen toxicity: the effect of inhalation of high concentrations of oxygen for twentyfour hours on normal men at sea level and at a simulated altitude of 18,000 feet. JAMA. 1945;128(10):710-717.

19. Jacobsen UP, Nielsen HB, Hidebrand F, et al. The chemical interactome space between the human host and the genetically defined gut metabotypes. ISME J. 2013;7(4):730-742.

36. Comroe JH, Dripps RD. The physiological basis for oxygen therapy: In: Pitts RF, ed. American lectures in physiology. No. 42. Springfield, IL: Charles C. Thomas; 1950.

20. Liu S, Shah SJ, Wilmes LJ, et al. Quantitative tissue oxygen measurement in multiple organs using 19F MRI in a rat model. Magn Reson Med. 2011;66:1722-1730.

37. Weschler RL, Dripps RD, Kety SS. Blood flow and oxygen consumption of the human brain during anesthesia produced by thiopental. Anesthesiology. 1951;12(3):308-314.

21. Olson KR. Hydrogen sulfide as an oxygen sensor. Clin Chem Lab Med. 2013;51(3):623-632.

38. Gerschman R, Gilbert DL, Nte SW, et al. Oxygen poisoning and x-irradiation: a mechanism in common. Science. 1954;119(3097):623-626.

22. Wolff CB. Oxygen delivery: the principal role of the circulation. Adv Exp Med Biol. 2013;789:37-42. 23. Kulkarni A, Kuppusamy P, Parinandi N. Oxygen, the lead actor in the pathophysiologic drama: enactment of the trinity of normoxia, hypoxia, and hyperoxia in disease and therapy. Antioxid Redox Signal. 2007;9(10):1717-1730. 24. Semenza G. Oxygen-dependent regulation of mitochondrial respiration by hypoxia-inducible factor 1. Biochem J. 2007;405(1):1-9.

39. Jacobson RM, Feinstein AR. Oxygen as a cause of blindness in premature infants: “autopsy” of a decade of errors in clinical epidemiological research. J Clin Epidemiol. 1992;45(11):1265-1287. 40. Martin DS, Grocott MPW. Oxygen therapy in anaesthesia: the yin and yang of O2. Br J Anaesth. 2013;111(6):867-871. 41. Gilbert-Kawai ET, Mitchell K, Martin D, et al. Permissive hypoxaemia versus normoxaemia for mechanically ventilated critically ill patients. Cochrane Database Syst Rev. 2014;5:CD009931.

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The Video Laryngoscopy Market:

KENNETH ROTHFIELD, MD Chairman Department of Anesthesiology Saint Agnes Hospital Baltimore, Maryland Adjunct Associate Professor Department of Organizational Systems and Adult Health University of Maryland School of Nursing Baltimore, Maryland

Dr. Rothfield has received research support in the form of equipment loans from AI Medical Devices, Ambu, Hanu Surgical Devices, Karl Storz, Truphatek, and Verathon Medical.

ver the past decade, video laryngoscopy has profoundly transformed airway management. Its recent inclusion in the American Society of Anesthesiologists Difficult

Airway Algorithm validates its adoption. Not surprisingly, the i l success off the h GlideScope Glid S (Verathon (V h Medical), M di l) the h commercial first mass-produced video laryngoscope (VL), has inspired many other companies to enter the airway management market.

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Some companies developed capital equipment to compete directly with Verathon; others have focused on low-cost devices, with an eye toward prehospital providers who currently have much less access to these devices. In recent years, the VL market has become crowded with devices that possess more similarities than differences. Although most VLs represent a substantial improvement over conventional laryngoscopy, the technology has not fully matured. The ultimate goal of making intubation foolproof has yet to be achieved. Device cost alone will not ensure market dominance. This review will discuss the current state of this evolving technology as well as provide predictions about the future.

A Highly Competitive Industry To successfully design, patent, manufacture, and market a medical device is no easy feat, requiring equal measures of ingenuity and capital. Even the most cleverly designed device will fail if it cannot be sold for a reasonable price, and with adequate sales volume and profit margin to create value for the company. Buyers of medical devices have substantial influence over the industry, particularly now that most hospitals are coping with the reorganization of US health care and shrinking revenue. Because the core technology used in VLs overlaps significantly with the mass-produced consumer electronics market, suppliers of key parts such as LCD screens and camera chips have little control over the industry. In addition, because devices do not require the same rigorous testing and clinical trials as pharmaceuticals, 510(k) FDA registration and entry into the market is easier. These factors help explain why competition in the VL market has become increasingly intense among many established companies as well as newcomers.

provide a high-quality view of the airway, even in patients with predictors of difficult laryngoscopy. This was confirmed by Aziz and colleagues, who demonstrated a 98% rate of success in more than 2,000 patients with anticipated difficult intubation.1 Challenges with placement of the ETT, however, frequently arise. Many of these problems are overcome with training and improved technique. For example, overzealous advancement of the VL blade lifts the trachea anteriorly from its normal anatomic position and may create a slight but critical misalignment between the tube and the glottis, making intubation impossible. This problem may be remediated simply by withdrawing the VL blade until the epiglottis comes into view. In other instances, the right arytenoid cartilage becomes an obstacle, snaring the ETT tip during insertion. Interestingly, there are reported situations in which direct laryngoscopy has rescued unsuccessful video laryngoscopy in which the vocal cords were visualized but tube placement was not possible. Therefore, despite the relatively easy airway visualization afforded by VLs, tube placement still requires adequate fine-motor skills and judgment, and successful tube delivery heavily relies on operator hand, wrist, and finger dexterity. It should be mentioned that visualization is not guaranteed because VL blades are rigid; the patient sometimes must be manipulated to â&#x20AC;&#x153;fit the device,â&#x20AC;? not the other way around. The steeply curved blades of several video devices follow a more natural path to the posterior pharynx, as opposed to flatter blades that compress and straighten the airway. However, acutely curved blades may solve one problem but create another. For example, Verathon recommends the use of a special rigid, steeply curved stylet for use with the GlideScope. Although

New Technologies Present New Human Factors Challenges Human factors refers to the interface of people and things. Engineers specializing in this field commit to improving the ease of use and efficacy of devices and systems. Human factors, therefore, is a helpful framework for considering the past, present, and future of video laryngoscopy. Historical approaches to laryngoscopy concentrated on displacing soft tissue between the oral opening and the glottis to create a narrow sight line. Not surprisingly, the main challenge of direct laryngoscopy is to obtain an adequate view of the glottic opening. Multiple factors, including patient anatomy and operator skill, may thwart successful direct laryngoscopy. Delivering the endotracheal tube (ETT) to its final destination, however, generally has been less vexing. VLs have reversed this situation: Visualization has become easy, but tube placement sometimes becomes difficult. Devices such as the GlideScope generally

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Figure 1.

The King Vision video laryngoscope eliminates the need for a stylet by incorporating a guiding channel for the endotracheal tube.

Turkstra et al reported that a standard stylet works just as well,2 this has not been the experience of the author, who has struggled with malleable stylet bending at the patient’s teeth during manipulation, particularly when attempting to steer the tube tip anteriorly. A clever but labor-intensive solution is to approach intubation as a team, with one operator using a VL and a second using a bronchoscope as an articulating stylet.3 Several newer VL devices have abandoned stylets altogether and incorporate a guiding channel within the blade of the instrument (Figure 1). In theory, this feature should simplify placement of the ETT. However, precise alignment of the channel and the glottis remains a prerequisite to successful intubation. The use of an angled bougie as a guide has been reported anecdotally to increase success with such devices. At the present time, however, there is no clear evidence of the superiority of channeled blades. Compared with the conventional laryngoscopy, merely inserting a VL into a patient’s mouth may be a struggle. Ease of blade insertion may be compromised with acutely curved VL blades. Furthermore, long handles and attached cables may contact the patient’s chest. Workarounds for these challenges include meticulous positioning (HELP [Head Elevated Laryngoscopy Positioning]) as well as introducing the blade at an angle. Finally, video laryngoscopy has been associated with proximal injuries to pharyngeal soft tissue, likely because nearly two-thirds of the course of the tracheal tube through the upper airway is not observed.

Figure 2.

The size of the video screen has not received much attention, but it merits consideration when deconstructed for human factors. Self-contained VLs incorporate a miniature LCD or organic light-emitting diode screen. Such devices are attractive for their portability compared with stand-mounted units and a separate monitor. However, small screens require the use of the operator’s near-field vision, which declines— sometimes substantially—after age 40 years. Use of near-field vision requires that the operator maintain a fixed orientation to the screen, with associated head movements to maintain focus. This position increases the physical complexity of the task for the provider. Furthermore, miniaturized images may impair dexterity—fine manipulation of the ETT during attempted intubation may be hard to discern on a tiny screen. Conversely, larger screens rely on the operator’s farfield vision, require much less deliberate focusing, and permit the operators to shift their gaze to other areas and back to the screen with ease. Because large screens present a magnified image of structures, dexterity may be improved as small motions and structures are seen clearly. Finally, like many other medical devices, some VLs may pose a risk for cross contamination and infection if meticulous reprocessing does not occur. For most of the emergency medical services market, the need for resterilization is a deal breaker, as paramedic vehicles lack this capacity.

Verathon GlideRite stylet (top); Truphatek TruFlex stylet (bottom).

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The Ideal VL As successful as video laryngoscopy has become, the current state of the art has room for improvement. Characteristics of the ideal VL include: • Lightweight and portable • Easy to insert with minimal patient manipulation • Conformable to individual patient anatomy • Reliable airway visualization despite fogging or interference from secretions • Permits accurate passage of the ETT with minimal fine-motor skills • Multiple display options (self-contained vs detached) • Image storage capability with integration into the electronic health record • No cleaning, reprocessing, or risk for cross contamination Although no single device currently possesses all of these characteristics, several new models have addressed some of the shortcomings of the current crop of VLs with the goal of simplifying intubation and making the products easier to use. To be commercially successful, devices must be both priced competitively and highly differentiated from each other.

Articulation: The Next Frontier Some devices that conform to individual patient anatomy are available, with more on the horizon. Articulating stylets show promise in decreasing the need for right-hand dexterity during tube delivery. During failed intubation, adequate alignment of the ETT and glottis is usually off by only a few millimeters. Ability to remotely control the ETT tip should remedy many of these situations. One potential solution is the TruFlex stylet (Truphatek). This reusable, stainless steel, articulating

Figure 3.

stylet is curved at the distal end and permits anterior tube tip displacement by actuating a lever. It is similar in appearance to the GlideRite stylet (Verathon Medical), but with a user-controlled angle of deflection. In theory, this feature may help in so-called “anterior” airways, or make up for imperfect placement of the laryngoscope blade (Figure 2). An initial pilot evaluation by one of the authors yielded favorable results.4 The simultaneous use of the GlideScope and a fiberoptic bronchoscope for tube guidance in the difficult airway has been previously reported (Figure 3).5 However, the routine use of a bronchoscope along with a VL requires 2 operators and is cost prohibitive. The Rapid Positioning Intubation Stylet (RPiS, Airway Management Enterprises) is a hybrid of a traditional stylet and a flexible bronchoscope (Figure 4). According to the manufacturer, the “RPiS is an airway rescue device for video and direct laryngoscopy which allows the hands of one provider to perform a similar method of intubating as the two provider method with a video laryngoscope and a fiber-optic bronchoscope. The RPiS is a dynamic stylet that can flex and retroflex at the tip, similar to a bronchoscope; however, it can be controlled with one hand while performing video or direct laryngoscopy with the other hand.”6 Articulation is not simply for stylets and tube guides. AI Medical Devices, Inc. has developed a fully articulating, guiding channel VL. Currently in prototype form, the FlexView VL features a portable inline LCD in addition to a lever that controls flexion of the distal section of the blade from a baseline of 40 degrees to a maximum of 110 degrees (Figure 5). Because the blade is gently curved in its baseline conformation, it may be more easily inserted into the oropharynx than other rigid VLs. The ETT is placed in a guiding channel without use of a separate stylet. Once in position,

Simultaneous use of a GlideScope and a video-enabled stylet enables 2 points of view for guidance of an endotracheal tube.

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the handle is squeezed to provide vertical compensation until the vocal cords are centered on the display and the ETT is advanced. Because the ETT is always in view, tissue trauma due to blind tube advancement is prevented. Although not currently available, the concept is intriguing and will merit thorough evaluation.

Simplifying Preoperative Airway Evaluation Visualizing the airway preoperatively may have tremendous value in planning anesthesia for patients with anatomical deformities, tumors, and other coexisting conditions that may complicate their clinical management. Preoperative endoscopic airway evaluation has been recommended to accomplish this.7 Similarly, emergency room physicians and otolaryngologists frequently are called on to evaluate patients with complex airway issues. Unfortunately, conventional endoscopic approaches require airway topicalization as well as a bronchoscope, the use of which demands expertise and technical support. Otolaryngologist Brad NaPier has developed a video-enabled, single-use oral airway that provides a high-quality view of the glottis and is so well tolerated that no topical anesthesia is necessary. Currently in the working prototype stage, the LarynGoView (Hanu Surgical Devices) has great potential for use in a variety of settings, including preoperative clinics, emergency departments, and otorhinolaryngology offices (Figure 6).

Figure 4.

The Rapid Positioning Intubation Stylet.

Robotic Intubation The use of robotics with intubation has been gaining some research attention. In the United States, the military-backed Telemedicine and Advanced Technology Research Center has sponsored research into an autonomous airway management system. The system, developed by Energid Technologies, would integrate force feedback and maintain full video tracking of the procedure for assisting an operator. A small pilot study with 12 patients involving the Kepler Intubation System, a hybrid of a robotic arm and VL, yielded a 91% success rate for intubation.8 Although this technology is in its infancy, it holds promise for further developments to assist clinicians lacking experience but who must perform advanced airway management. Although the current state of the art in video laryngoscopy has effectively solved the problem of obtaining an adequate laryngeal view, there is room for device improvement to make placement of the ETT more precise. Whether it is through user-enabled articulation, robotics, or other approaches, patients deserve to reap the benefits of these advanced approaches to airway management. As the marketplace advances and matures, we will ultimately come closer to the ideal VL.

Figure 5.

FlexView VL. Squeezing the handle articulates the blade and steers the tip of the endotracheal tube anteriorly.

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Figure 6.

The LarynGoView (prototype) is a modified bite block with a built-in solid-state image which provides an image of the glottis in unanesthetized patients.

References 1.

Aziz MF1, Healy D, Kheterpal S, et al. Routine clinical practice effectiveness of the Glidescope in difficult airway management: an analysis of 2,004 Glidescope intubations, complications, and failures from two institutions. Anesthesiology. 2011;114(1):34-41.

2. Turkstra TP, Harle CC, Armstrong KP, et al. The GlideScopespecific rigid stylet and standard malleable stylet are equally effective for GlideScope use. Can J Anesth. 2007;54(11):891-896. 3. Doyle JD. GlideScope-assisted fiberoptic intubation: a new airway teaching method. Anesthesiology. 2004:101(5):1252. 4. Rothfield KP, Lopez K, Langlois S, et al. Usability of the TruFlex articulating stylet for videolaryngoscopy. American Society of Anesthesiologists Annual Meeting; October 14, 2013; San Francisco, CA. Abstract A3221.

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5. Sharma D, Kim L, Ghodke B. Successful airway management with combined Use of Glidescope videolaryngoscope and fiberoptic bronchoscope in a patient with Cowden Syndrome. Anesthesiology. 2010;113(1):253-255. 6. Personal communication with company. 7. Rosenblatt W, Ianus AI, Sukhupragarn W, et al. Preoperative endoscopic airway examination (PEAE) provides superior airway information and may reduce the use of unnecessary awake intubation. Anesth Analg. 2011;112(3):602-607. 8. Hemmerling TM1, Taddei R, Wehbe M, et al. First robotic tracheal intubations in humans using the Kepler intubation system. Br J Anaesth. 2012;108(6):1011-1016.

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REFERENCE 1 Kus, et al. A Comparison of the EZ-Blocker with a Cohen Flex-Tip Blocker for One-Lung Ventilation. Journal of Cardiothoracic and Vascular Anesthesia. 2013; August 19: ISSN 1532-8422.

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Advancements Lung Isolation WANDA M. POPESCU, MD Associate Professor of Anesthesiology Yale University School of Medicine New Haven, Connecticut Dr. Popescu reports no relevant financial conflicts of interest.

ecent impressive technologic

advancements have led to the development of a wide variety of

minimally invasive surgical techniques. Cardiothoracic surgery is no exception. In the United States, video-assisted thoracosc copic surgery is being used in 25% to 50% of lung resection surgeries.1,2 Since its approvall by the FDA in 2001, the da Vinci robotic c surgery system (Intuitive Surgical) has significantly increased its presence in th he cardiothoracic operating room.3

Nevertheless, only in the past few years has it been demonstrated that minimally invasive thoracic surgery improves outcomes compared with standard thoracotomy.4,5 However, one of the key elements for the success of these techniques is excellent lung isolation that allows optimal surgical visualization. A poorly collapsed lung leads to complications, prolongs surgical time, and mitigates the overall advantages of a minimally invasive technique.3 Therefore, anesthesiologists should feel comfortable when placing and managing all available devices for lung separation. This article describes the currently used lung separation devices, new concepts in ventilatory approaches, and potential strategies to prevent desaturation during one-lung ventilation (OLV). Double-lumen tubes (DLTs), bronchial blockers

(BBs), the Univent (Teleflex) tube, and single-lumen endotracheal tubes (ETTs) represent the currently available devices used for OLV. Indications for OLV are presented in Table 1.

Double-Lumen Tubes The DLT is the most commonly used device for OLV. It is essentially composed of 2 polyvinyl chloride ETTs sealed together. The longer of the 2 tubes is designed to fit endobronchially. This represents the “bronchial lumen.” The other tube, with its end in the trachea, represents the “tracheal lumen.” Each tube has its own cuff. To be easily distinguished during flexible bronchoscopy, the bronchial cuff and the pilot balloon serving the cuff are blue. To allow facile insertion in

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the desired bronchus, the DLT has a fixed, predesigned curvature.6 The tube also has a stylet placed through the bronchial lumen. Because the bronchial anatomy of the left side differs from that of the right, separate left- and rightsided DLTs are available. The bronchial lumen of the right DLT is provided with a ventilation slot, which requires proper alignment with the right upper lobe bronchus takeoff. DLTs come in different sizes.

Table 1. Indications for One-Lung Ventilation Absolute indications Prevention of contamination of the healthy lung from the contralateral diseased lung Pulmonary hemorrhage Lung abscess or infected lung cyst Differential ventilation Bronchopleural fistula Bronchopleural cutaneous fistula Large unilateral bullae Large bronchial trauma Severe unilateral lung contusion After unilateral lung transplant when both lungs have significantly different compliances Lung lavage Surgical indications Video-assisted thoracoscopic surgery Robotic-assisted thoracoscopic surgery Robotic-assisted minimally invasive cardiac surgery Relative indications High-priority surgical exposure

A pediatric left DLT is available in 28 F. Adult sizes include a left 32 F and left and right DLTs in 35, 37, 39, and 41 F. Measuring the tracheal or bronchial size on a chest roentgenogram or computed tomography scan can aid in choosing the appropriately sized DLT. However, as a rule of thumb, either a 35 or 37 F DLT is suitable for women, whereas 39 or 41 F is appropriate for men (Figure 1).7 Before placement, the DLT and the stylet are well lubricated and the cuffs are tested. The DLT is inserted either using direct or indirect laryngoscopy. If direct laryngoscopy (DL) is chosen, a Macintosh blade ideally should be used as it offers more space for tube manipulation. The DLT is initially inserted with the curvature upward. After the bronchial cuff passes the vocal cords, the DLT is rotated 90 degrees toward the appropriate side and advanced until slight resistance is met. To decrease the risk for tracheobronchial injury, some clinicians prefer to remove the stylet when the tube is advanced endobronchially. Alternatively, the DLT can be placed in the trachea using DL and guided into the desired bronchus using the flexible bronchoscope. If DL does not offer a good glottic view, other techniques may be employed. When a video laryngoscope is used to place a DLT, a longer stylet, with a curvature similar to the intubating blade, is required. The DLT also can be positioned using a flexible bronchoscope from the start. In this case, the scope should be loaded through the bronchial lumen. Regardless of the placement method, auscultation for breath sounds and flexible bronchoscopy (FB) are required to verify the position of the DLT. When auscultating, both cuffs should be inflated and breath sounds should be present bilaterally and equally. Following this maneuver, each lumen is clamped sequentially and breath sounds should be present only in the contralateral lung. However, this technique detects only a proper right/left position and has a large margin of error.8 Therefore, in modern thoracic anesthesiology, FB is highly recommended.

Upper lobectomy via thoracotomy Pneumonectomy Lung volume reduction surgery Open thoracic aortic aneurysm repair Minimally invasive cardiac surgery Low-priority surgical exposure Esophageal surgery via thoracotomy Middle and lower lobectomies performed via thoracotomy Thymectomy Sympathectomy Thoracic spine surgery Source: http://www.openanesthesia.org/One_Lung_ Ventilation. Accessed July 20, 2014.

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Figure 1. Left double-lumen tube with connector and special suction catheter.

The flexible bronchoscope is initially positioned through the tracheal lumen. This location should offer a good view of the primary carina—the division between the right and left bronchi—with the blue bronchial cuff visible either at carinal level or 1 to 2 mm into the bronchus, depending on the brand of DLT. Subsequently, the flexible bronchoscope is passed through the bronchial lumen. In the case of a left DLT, the secondary carina—the division between the left upper and lower bronchi—should be visualized. However, in the case of a right DLT, the typical trifurcation into the right middle lobe, basilar, and superior segments of the right lower lobe should be observed. When the flexible bronchoscope is withdrawn into the bronchial lumen, the ventilating slot should be identified and it should be confirmed that it is properly aligned with the right upper lobe bronchus takeoff. The DLT position should be checked immediately after intubation and after any change in the patient’s position. Desaturation, increased airway pressures, or loss of lung isolation should prompt an immediate bronchoscopic evaluation. To facilitate observation of the DLT position and to quickly identify and solve placement problems, a special tube has been developed. The VivaSight-DL (ETView Medical Ltd.) has a high-resolution camera at the tip of the tracheal lumen (Figure 2). The camera is connected to a monitor and allows continuous visualization of the tracheal carina. Any dislodgement is easily observed and the correct position is reestablished. Therefore, the need for FB is decreased. However, to confirm correct positioning above the secondary carina, FB through the bronchial lumen should be performed after initial intubation. The additional advantage of this device is that ventilation is unaffected while the airway is observed. The VivaSight-DL is available only in left-sided sizes 37, 39, and 41 F.

DLTs have several advantages over other devices for OLV. Both lumens have large diameters, offering low resistance to gas flow. Suction catheters can be passed through the lumens, allowing the clearing of secretions from both lungs. Similarly, low-flow oxygen insufflation or continuous positive airway pressure (CPAP) can be applied to the nonventilated lung. The FB also can be used on the operative side to inspect the bronchial anastomosis, as required in lung transplant or sleeve pneumonectomy. In comparison with BB, the lung collapse achieved with a DLT is faster. Left DLTs have a lower incidence of dislodgements and malpositionings.9 However, the right DLT can easily obstruct the takeoff of the right upper lobe bronchus, leading to hypoxemia or inadequate collapse of the right lung. Because the DLT has both a tracheal and bronchial cuff, it is the only device that protects the healthy lung from contamination with either pus or blood from the diseased contralateral lung. The DLT also permits differential ventilation using 2 separate ventilators in situations in which compliance of the right and left lung differ significantly, such as after unilateral lung transplant or severe pulmonary contusion. However, DLTs should not be used in the ICU except in extreme clinical situations because ICU personnel generally are not familiar with the specifics of this particular device. Therefore, for patients who require postoperative ventilation, the DLT should be changed to a regular ETT at the completion of surgery. The main disadvantage of DLTs is their large size, which may prove problematic during a difficult intubation. For patients with small oral apertures, the teeth can puncture the tracheal cuff during insertion. And for patients with a distorted left bronchial anatomy, such as after a left upper lobectomy, a stiff DLT may be impossible to position.10,11 Table 2 describes advantages and disadvantages of DLTs compared to BBs and Univent

Table 2. Advantages/Disadvantages of Lung Isolation Devices Left DLT

Right DLT

Univent

Ease of positioning

Displacement risk

Suctioning

Separate ventilation

Postoperative ventilation

Figure 2. The VivaSight-DL.

Difficult airway

A: Double-lumen tube with camera at tracheal lumen tip. B: External monitor allows continuous visualization of the tracheal carina.

Lobar isolation

Courtesy of Dr. J. Campos.

BB, bronchial blocker; DLT, double-lumen tube

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tubes. Another new device available for clinical practice is the Silbroncho (Fuji Systems), a silicone DLT with a malleable design (Figure 3). The bronchial lumen is reinforced by wire to prevent kinking. This provides flexibility to allow the tube to follow the patientâ&#x20AC;&#x2122;s anatomy and is less likely to damage the tracheobronchial tree during intubation. Moreover, the silicone cuff is more resistant to tearing on the teeth. The decision to exchange the DLT for an ETT requires the clinician to perform a riskâ&#x20AC;&#x201C;benefit analysis. As previously mentioned, critical care personnel typically are not familiar with the particularities of these devices. Therefore, any dislodgement can lead to difficulties in ventilation, hypoxia and, if not corrected immediately, even death. However, the potential for loss of the airway during tube exchange should not be dismissed. Clinicians must consider all the safety precautions to avoid loss of the airway. If the surgery was prolonged and the patient required massive fluid resuscitation, it is likely

that significant airway edema will be present. In such circumstances, use of an airway exchange catheter (AEC) when performing the tube exchange is advisable.12 A longer catheter, specially designed for use with DLTs, is optimal. The AEC serves a dual purpose: It acts as a guide to the airway and it permits jet ventilation through its central lumen (Figure 4).

Bronchial Blockers Bronchial blockers are alternative devices used for lung separation and OLV. Their design derives from vascular Fogarty catheters. The BB is a long, semirigid catheter with a central lumen through its entire length that allows lung deflation and an inflatable balloon at the tip. The BB is positioned within the ETT. A provided multiport adapter connects the ETT with

Figure 5. Uniblocker set. Wire loop protruding from distal tip maintains tip angulation until it is removed just before use. Proximal wire stylet also is removed before use.

Figure 3. Silbroncho double-lumen tube.

Figure 6. Arndt Endobronchial Blocker. Figure 4. Airway exchange catheter.

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Note wire loop protruding from distal tip of blocker below balloon.

the ventilator circuit and allows for concomitant coaxial placement of the BB and a flexible bronchoscope. Under direct flexible bronchoscopic guidance, the BB is advanced in the desired bronchus and the cuff is inflated to seal the bronchus. At this point, ventilation to the lung with the blocker ceases. Five types of BB currently are available: the Uniblocker (Fuji Systems), the Arndt wire-guided endobronchial blocker (EBB; Cook Medical), the Cohen EBB (Cook Medical), the EZ-Blocker (Teleflex), and the VivaSight EBB (ETView Medical Ltd.). Each of these devices has specific characteristics to allow for a more facile placement of the BB (Table 3). The Uniblocker shaft is manufactured with a wire mesh coated with polyurethane that confers torque control and allows adequate movement transmission from the top to the tip (Figure 5). To facilitate endobronchial insertion, the shaft is designed with a fixed “hockey stick” curvature and the central lumen has a metallic stylet, which is removed after initial placement.13 The device’s silicone high-volume balloon is impermeable to gas exchange and the cuff, even when inflated to its maximal capacity of 8 mL of air, provides reliably safe endobronchial pressures below 30 mm Hg. The Arndt EBB has a plastic-coated nylon wire that extends through the entire length of the central lumen and forms a loop at the end (Figure 6). The flexible bronchoscope is passed through the loop and the EBB is inserted using 2 techniques. If the loop is cinched tightly to the flexible bronchoscope, both the EBB and the flexible bronchoscope travel together into the desired bronchus. Alternatively, with the loop loosened, the flexible bronchoscope guides the EBB

toward the endobronchial position. Choosing the insertion technique depends on the preference of the operator. The wire loop is removed after initial placement, making the Arndt EBB slightly more cumbersome to reposition. The Arndt EBB is the only blocker with 2 available shapes of high-volume, low-pressure balloons, spherical or elliptical. The spherical balloon is 1 to 2 cm long and is designed particularly for the right mainstem bronchus; the elliptical balloon is for the left mainstem bronchus.14,15 The Cohen EBB has a turning wheel at its most proximal part, which allows deployment of the preangled distal tip in the desired bronchus (Figure 7). At the 55 cm mark, the blocker has a torque grip that facilitates rotation. The device has a spherical high-volume, low-pressure balloon at its tip. Above the balloon is an arrow indicating in which direction the tip will deflect. The internal lumen is rather narrow and complete passive lung collapse takes time. Therefore, the Cohen EBB has a cone-shaped device that attaches to the proximal end and, when connected to the suction circuit, speeds deflation of the lung. Its flexible tip and steering mechanism make the Cohen EBB particularly useful for procedures requiring selective lobar blockade.15,16 However, novice users may find the design cumbersome to manipulate.17 The EZ-Blocker has a unique design (Figure 8). The main shaft splits into a Y-shaped end that emulates the tracheobronchial anatomy. The 2 distal ends are 4 cm long and carry a spherical balloon. The 2 cuffs and their pilot balloons are color-coded: One is blue and the other is yellow. As opposed to other blockers, however, the cuffs are high-pressure, low-volume. As with other blockers, the shaft and the ends of the

Table 3. Bronchial Blocker Specifications Uniblocker

Arndt Blocker

Cohen Blocker

EZ-Blocker

Size

5 F, 9 F

5 F, 7 F, 9 F

Balloon shape

Spherical

Spherical (S) Elliptical (E)

Spherical

Two spherical (left and right)

Maximum balloon volume

3 cc for 5 F 8 cc for 9 F

2 cc for 5 F 6 cc for 7 F 8 cc for 9 F (S) 12 cc for 9 F (E)

8 cc

6.9 cc for left 9.1 cc for right

Central channel

2.0 mm for 9 F

1.4 mm for 9 F

1.6 mm

4 very small channels

Guidance mechanism

Preshaped tip

Nylon wire loop

Wheel device

None

Smallest ETT required

4.5 ETT for 5 F 8.0 ETT for 9 F

4.5 ETT for 5 F 6.0 ETT for 7 F 7.5 ETT for 9 F

8.0 ETT

7.0 ETT

ETT, endotracheal tube

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EZ-Blocker have a central lumen to allow for lung deflation. These lumens are narrow and lung collapse takes a long time even with suction. The split ends of the device have a natural tendency to go into the left and right bronchi. Therefore, it can be introduced blindly or under direct flexible bronchoscopic guidance. When positioned blindly, the EZ-Blocker should be advanced until slight resistance is met, which corresponds to the contact of the bifurcated blocker end with the tracheal carina. After a blind placement, FB is required to verify correct position and to identify which cuff corresponds to which bronchus.18 The anesthesiologist should label each cuff once the bronchoscopic examination is completed. In general, the EZ-Blocker is easier to position than the other BBs.19 Nevertheless, there is a chance that both ends can enter the right mainstem bronchus. To avoid this problem during blind placement, 2 rules must be followed: The distal tip of the ETT must be at least 4 cm above the carina and the blocker should be inserted with the distal ends in a horizontal plane. Because of its construction, this blocker is quite stable and is less prone to dislodgement than other

Figure 7. Cohen Tip Deflecting Endobronchial Blocker (shown with Cook Multiport Adapter).

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devices20—making it particularly useful in situations such as prone esophagectomy in which lung isolation is required but access to the airway is limited. Because it can be successfully and rapidly placed blindly, it is extremely useful for patients with chest trauma and other emergency situations in which the airway is bloody and lung separation is required for surgery. The newest device on the market is the VivaSight EB, which consists of a steerable balloon catheter with a high-resolution camera at its tip, which is connected to an external monitor that enables real-time video imaging guidance. The blocker is compatible with a standard ETT, in which case FB is still required to observe the position of the blocker and inflation of the cuff. However, if the VivaSight is used with the VivaSight-SL—a single-lumen ETT with high-resolution video camera at the tip—the need for FB is obviated.21 This blocker functions in a similar manner to other BBs, with the advantage that, unlike the others, it provides real-time visualization below the tip. One of the advantages of BBs is that their deployment requires no larger than a 7.5-mm ETT or an 8-mm cuffed tracheostomy tube. This feature is particularly

Figure 8. The EZ-Blocker. Note the bifurcated symmetrical ends with color-coded balloons and corresponding cuffs. Courtesy of Dr. A. Neyrinck.

useful for patients with difficult airways or for those who arrive in the operating room already intubated.22 Moreover, selective endolobar blockade can be accomplished with BBs in patients who have undergone previous lung resection surgery or who have significant pulmonary disease and do not tolerate OLV. For patients who require postoperative ventilation, removal of the BB leaves the ETT in place and avoids the need for tube exchange. However, when compared with DLTs, BBs are more prone to intraoperative dislodgements and lung collapse takes longer to complete.23 They also do not permit the suctioning of secretions or the inspection of the operative-side bronchus. The clinician can use several strategies to insert a BB and hasten lung collapse. Before placement of the device, the patient should be ventilated with 100% oxygen to promote the development of absorption atelectasis. This technique helps lung collapse at the time OLV is initiated. Placing the ETT higher in the trachea generates more space to manipulate the BB and guide it toward the desired bronchus. If it is difficult to steer the BB towards the desired bronchus, turning the patient’s head in the opposite direction may be helpful. Before inflating the balloon, disconnect the patient from the ventilator and allow him or her to exhale passively. The balloon should be inflated with 6 to 8 cc of air under bronchoscopic visualization, making sure that the cuff completely seals the bronchus. Mild suction can be applied to the proximal part of the BB; some blockers allow connection to the suction circuit. Reinstitution of ventilation should be performed after these maneuvers are completed.

Univent The Univent is a single-lumen silicone ETT with a secondary small lumen along the anterior concave wall containing a BB (Figure 9). The blocker can extend 8 to 10 cm outside the lumen and carries a high-pressure, low-volume balloon. When performing the initial intubation, the clinician should withdraw the Univent into the lumen. The blocker then is extended and guided into the desired bronchus under bronchoscopic visualization. The Univent functions similar to other BBs,24 but has some distinct disadvantages. When the device is extended or withdrawn into the lumen, the cuff may tear. The outer diameter of the 8.0 Univent tube is similar to that of a 41 F DLT. Therefore, its size does not justify using it in lieu of a DLT when lung separation is required. Finally, the Univent’s relatively high cost and the presence of many alternatives make it a rarely used option at this time.

endobronchial tubes are mostly used in the pediatric population because small DLTs are not available. Additionally, in cases of massive pulmonary hemorrhage, such as a ruptured pulmonary artery, the easiest and fastest way to achieve lung isolation is endobronchial intubation. Special endobronchial tubes with an angulated distal tip and 2 cuffs, one in a bronchial and the other in a tracheal position, are available. Endobronchial tubes can be placed under flexible bronchoscopic guidance or blindly. The chance of placing a tube in the left mainstem bronchus is greater if the head of the patient is turned to the right. However, elective use of these tubes for minimally invasive surgical procedures is not recommended, as lung collapse is suboptimal.

Protective Strategies for Lung Ventilation The most feared complication after thoracic surgery is the development of acute lung injury (ALI), which is associated with extremely high mortality. The pathogenesis of ALI is multifactorial and involves preexisting patient conditions, such as radiation therapy, surgeryinduced activation of inflammatory mediators, intraoperative ventilatory strategies, fluid management, and transfusion of blood and blood products. Some of these risk factors are modifiable but others cannot be mitigated. In an attempt to maintain adequate oxygenation and prevent the development of atelectasis and shunt, the traditional OLV strategy required maintenance of similar parameters used during 2-lung ventilation. Lung hyperinflation, hyperoxia resulting in oxidative stress, and the mechanical stress of the opening and closing alveoli may lead to the release of proinflammatory mediators.25,26 However, more recent studies have demonstrated that protective lung ventilation strategies used during OLV improve postoperative outcomes and reduce the incidence of ALI.27,28 Therefore, state-of-the-art management of OLV requires protective lung ventilation strategies. These consist of using small tidal volumes—5 to 6 cc/kg—in conjunction with positive end-expiratory pressure (PEEP) at 5 to 10 cm H2O; a respiratory rate

Endobronchial Tubes As a last resort in clinical emergencies requiring OLV, when exchanging an ETT for a DLT is considered too hazardous and placement of BB is impossible because of blood and secretions in the airway, advancement of the ETT already in place into an endobronchial position can be considered. In certain situations, the ETT may be too short for an endobronchial position. Single-lumen

Figure 9. Univent tube.

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adequate to maintain normocapnia; and a plateau pressure below 20 cm H2O. The use of a fraction of inspired oxygen (FiO2) of 100% has been unquestioned for many years. However, some data suggest that patients ventilated with 100% FiO2 experience an increase in the inflammatory mediators interleukin-6 and -8 compared with patients receiving lower FiO2.27 Before implementing 100% FiO2 during OLV V, a better approach is to evaluate the need for a high level of oxygen in each individual case. Lower FiO2 has been successfully used during OLV without significant episodes of desaturation.

Management of Hypoxia During OLV Before determining the optimal management of hypoxia during OLV, the clinician must understand the pathophysiology of hypoxia. Traditionally, anesthesiologists desire maximal oxygen saturation (SaO2) to create a reserve in case of emergency. A decrease in SaO2 under 2-lung ventilation implies the possibility of underlying pathology. However, under OLV conditions, the SaO2 decreases as a result of the induced shunt. In such cases, it may be more prudent to tolerate SaO2 to 88% for short periods of time rather than perform maneuvers to increase the SaO2 that could prove more detrimental to the overall long-term outcome. For persistent desaturations that demand treatment, a predetermined plan is essential. The first step is to assess the position of the lung isolation device. Flexible bronchoscopy allows for immediate detection of malpositioning of the device as well as mucus plugs or blood in the ventilated lung. The next maneuver is to increase PEEP (up to 10 cm H2O) to the ventilated lung. Values higher than 10 cm H2O may worsen hypoxia by counteracting the hypoxic pulmonary vasoconstriction effect and diverting blood toward the nonventilated lung. If a lower FiO2 is used, it should be increased to 100%. CPAP to the nonventilated lung is an acceptable strategy only in open thoracotomies. However, in video- or

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robotic-assisted cardiothoracic surgery, applying CPAP should be avoided as it reduces surgical visualization and prolongs, or even prevents, the operation. Applying intermittent recruiting maneuvers to the ventilated lung is an effective strategy in both preventing and treating hypoxemia. If a DLT is used, a suction catheter connected to the auxiliary oxygen port can be inserted in the lumen of the nonventilated lung. This form of â&#x20AC;&#x153;blow byâ&#x20AC;? does not produce lung inflation, as the gas entered has space to exit, but provides some oxygenation to the blood perfusing this lung.29 If a pneumonectomy is performed, clamping the pulmonary artery will eliminate entirely the shunt. Ultimately, if low saturations, which are potentially deleterious to the patient, persist despite the above maneuvers, returning temporarily to 2-lung ventilation should be considered. This strategy should be discussed with the surgical team.

Conclusion Minimally invasive techniques are becoming a predominant component of thoracic and cardiac surgery. Now more than ever, therefore, anesthesiologists must be adept at performing lung isolation. A wide variety of devices are currently available for clinical practice, the most widely used of which is the left DLT. Bronchial blockers are particularly advantageous in patients with difficult airways who require postoperative ventilation, who have a tracheostomy in place, or who require selective endolobar blockade. Use of FB is mandatory in identifying correct device position and in repositioning displaced devices. In modern thoracic anesthesia, the use of protective lung ventilation strategies has become standard of care. To best meet the changing clinical scenarios of each individual patient and the various surgical requirements, anesthesiologists should feel comfortable placing and managing a variety of lung isolation devices as well as with performing FB.

References 1.

Cooke DT, Wisner DH. Who performs complex noncardiac thoracic surgery in United States academic medical centers? Ann Thorac Surg. 2012;94(4):1060-1064.

2. Boffa DJ, Allen MS, Grab JD, et al. Data from the Society of Thoracic Surgeons General Thoracic Surgery database: the surgical management of primary lung tumors. J Thorac Cardiovasc Surg. 2008;135(2):247-254. 3. Kim AW, Detterbeck FC. Innovations in thoracic surgery. Curr Opin Anesthesiol. 2013;26(1):13-19. 4. Paul S, Altorki NK, Sheng S, et al. Thoracoscopic lobectomy is associated with lower morbidity than open lobectomy: a propensity-matched analysis from the STS database. J Thorac Cardiovasc Surg. 2010;139(2):366-378. 5. Swanson SJ, Meyers BF, Gunnarsson CL, et al. Video-assisted thoracoscopic lobectomy is less costly and morbid than open lobectomy: a retrospective multiinstitutional database analysis. Ann Thorac Surg. 2012;93(4):1027-1032.

16. Campos JH. Which device should be considered the best for lung isolation: double-lumen endotracheal tube versus bronchial blockers. Curr Opin Anaesthesiol. 2007;20(1):27-31. 17. Campos JH, Hallam EA, Van Natta T, et al. Devices for lung isolation used by anesthesiologists with limited thoracic experience: comparison of double-lumen endotracheal tube, Univent torque control blocker, and Arndt wire-guided endobronchial blocker. Anesthesiology. 2006;104(2):261-266. 18. Végh T1, Juhász M, Enyedi A, et al. Clinical experience with a new endobrochial blocker: the EZ-blocker. J Anesth. 2012;26 (3):375-380. 19. Mourisse J, Liesveld J, Verhagen A, et al. Efficiency, efficacy, and safety of EZ-blocker compared with left-sided double-lumen tube for one-lung ventilation. Anesthesiology. 2013;118(3):550-561. 20. Ruetzler K, Grubhofer G, Schmid W, et al. Randomized clinical trial comparing double-lumen tube and EZ-Blocker for single-lung ventilation. Br J Anaesth. 2011;106(6):896-902.

6. Campos JH. Lung isolation techniques. Anesthesiol Clin North America. 2001;19(3):455.

21. Giglio M, Oreste D, Oreste N. Usefulness of ETView TVT endotracheal tube for correct positioning of bronchial blockers in left lobectomy: an easy and safe combination. Minerva Anesthesiologica. 2009;75(suppl 1):1-4.

7. Pedoto A. How to choose the double-lumen tube size and side: the eternal debate. Anesthesiol Clin. 2012;30(4):671-681.

22. Campos JH. Lung isolation techniques for patients with difficult airway. Curr Opin Anesthesiol. 2010;23(1):12-17.

8. Smith BG, Hirsch NP, Ehrenwerth J. Placement of double lumen endobronchial tubes. Br J Anaesth. 1986;58(11):1317-1320.

23. Narayanaswamy, M, McRae K, Slinger P, et al. Choosing a lung isolation device for thoracic surgery: a randomized trial of three bronchial blockers versus double lumen tubes. Anesth Analg. 2009;108(4):1097-1101.

9. Slinger P. Con: the new bronchial blockers are not preferable to double-lumen tubes for lung isolation. J Cardiothorac Vasc Anesth. 2008;22(6):925-929. 10. Suriani RJ, Konstadt SN, Camunas J, et al. Transesophageal echocardiographic detection of left atrial involvement in a lung tumor. J Cardiotorac Vasc Anesth. 1993;7(1):73. 11. Lohsher J, Brodsky J. Silibroncho double-lumen tube. J Cardiothorac Vasc Anesth. 2006;20(1):129. 12. Gatell JA, Barst SM, Desiderio DP, et al. A new technique for replacing an endobronchial double-lumen tube with an endotracheal single-lumen tube. Anesthesiology. 1990;73(2):340-341. 13. Campos J. Lung Isolation. In: Slinger P, ed. Principles and Practice of Anesthesia for Thoracic Surgery. New York, NY: Springer; 2011:227-246.

24. Campos JH, Kernstine K. A comparison of a left-sided bronchocath with the torque control blocker Univent and the wire-guided blocker. Anesth Analg. 2003;96(1):283-289. 25. Licker M, de Perrot M, Spiliopoulos A, et al. Risk factors for acute lung injury after thoracic surgery for lung cancer. Anesth Analg. 2003;97(6):1558-1565. 26. Jordan S, Mitchell JA, Quinlan GJ, et al. The pathogenesis of lung injury following pulmonary resection. Eur Respir J. 2000;15(4):790–799. 27. Michelet P, D’Journo XB, Roch A, et al. Protective ventilation inﬂuences systemic inﬂammation after esophagectomy: a randomized controlled study. Anesthesiology. 2006;105(5):911-919.

14. Neustein, S. The use of bronchial blockers for providing one-lung ventilation. J Cardiothorac Vasc Anesth. 2009;23(6):860-868.

28. Licker M, Diaper J, Villiger Y, et al. Impact of intraoperative lungprotective interventions in patients undergoing lung cancer surgery. Crit Care. 2009;13(2):R41.

15. Dumans-Nizard V, Liu N, Laloë PA, et al. A comparison of the deflecting-tip bronchial blocker with a wire-guided blocker or left-sided double-lumen tube. J Cardiothorac Vasc Anesth. 2009;23(4):501-505.

29. Grichnik KP, Shaw A. Update on one-lung ventilation: the use of continuous positive airway pressure ventilation and positive endexpiratory pressure ventilation—clinical application. Curr Opin Anesthesiol. 2009;22(1):22-30.

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Surgical Management Of the Failed Airway: A Guide To Percutaneous Cricothyrotomy

JOAN E. SPIEGEL, MD

VIPUL SHAH, MD

Assistant Professor Beth Israel Deaconess Medical Center Harvard Medical School Boston, Massachusetts

Western Washington Medical Group Everett, Washington

The authors report no relevant financial conflicts of interest.

he first-known mention of an attempted surgical airway, a

tracheostomy, was depicted on Egyptian tablets as early as 3,600 BCE.

History has condemned the emergent surgical airway when

it has failed, but when successful, the physicians who performed it have risen in esteem to become “on a footing with the gods.” A N E S T H E S I O L O G Y N E W S G U I D E T O A I R WAY M A N A G E M E N T 2 0 1 4

In 100 BCE, the Persian physician Asclepiades described in detail a tracheal incision for improving the airway.1 Yet most who advocated surgical approaches to the airway, including Asclepiades, were severely criticized. Vicq d’Azyr, a French surgeon and anatomist, first described cricothyrotomy in 1805. Emergent cricothyroidotomy (also known as cricothyrotomy, minitracheostomy, and high tracheostomy) became widely acknowledged and accepted in 1976 when Brantigan and Grow confirmed the relative safety of the procedure.2 A decade later, the Seldinger technique, a wire-over-needle procedure commonly used for intravascular cannulation, was adapted for use in obtaining both emergent and nonemergent surgical airways. The 3 procedures that might be considered in an emergency airway setting include needle cricothyrotomy (with or without jet ventilation), surgical cricothyrotomy (traditional 4-step or percutaneous), and tracheostomy. For anesthetists and other nonsurgical specialists, learning needle or percutaneous cricothyrotomy may be more suitable than the more complicated surgical alternatives. The complication rate for emergent cricothyrotomy is substantial, ranging from 10% to 40% of cases.3 Emergent cricothyrotomy is not a procedure that is easily practiced for “real-life” situations. For the anesthesiologist, the decision to abandon traditional intubation and supraglottic ventilation methods for a surgical approach is emotionally difficult. The difficulty is compounded when the physician faces an emergent situation with no time for adequate preparation and discussion. Psychological preparation throughout one’s career, therefore, is the single most important aspect of training for failed airway situations; not surprisingly, it is stressed repeatedly in numerous publications, including the Anesthesia Patient Safety Foundation’s guidance on the topic.4 Exposure to the procedure through simulation may improve the chance of success, but given that not all providers have access to simulation centers, for

Table 1. Indications for Cricothyrotomy Upper airway hemorrhage

most clinicians, the first opportunity to perform the procedure will be on a patient who cannot be intubated or ventilated. Simulation may even improve the chance of success when the only instruments available are a pocketknife and ballpoint pen (although this is highly discouraged). Emergent cricothyrotomy remains a high-risk, low-frequency event that is ideally practiced in simulation centers on mannequins and cadavers. All physicians who deal with the airway should attempt to obtain proficiency in at least one surgically invasive method.

Indications Certain pathologic conditions in oropharyngeal anatomy may predispose a patient to difficult routine airway management. These include infection, trauma, endocrine disorders, foreign bodies, inflammatory conditions, tumors, and certain physiologic anomalies (Table 1). The rate of performed emergent surgical airways in the out-of-hospital setting is 10 times the rate of the in-hospital setting. In the emergency room arena, the rate is about 1% (of all secured airways), and about 0.1% in the operating room or intensive care setting.5 The doctrine that supports performing any surgical airway is the following: A surgical airway should be attempted in order to save the life of an obtunded patient who cannot be ventilated by any other means. In other words, the final cannot-intubate, cannot-oxygenate option in all airway management algorithms is the insertion of an endotracheal tube (ETT) via cricothyrotomy.4 Once the decision is made to perform an emergent surgical airway, no absolute contraindications remain in adults (Table 2); it is a last-resort, lifesaving measure, as it is presumed that less-invasive methods have been tried in an attempt to ventilate the patient. (The exception being children under the age of 10 years, including neonates, for whom incision through the cricothyroid membrane may cause irreparable damage and for whom needle cricothyrotomy is the method of choice.) When time is available, the most experienced surgical clinician should always be consulted first. When no experienced surgeon is available and one’s inexperience or fears preclude action, a larger-bore angiocatheter should be placed into the trachea, and attached to a low-pressure oxygen source at 15 L per minute.

Midfacial fractures Abnormal facial anatomy Acquired Congenital Airway trauma Inhalational or thermal Foreign body Laryngeal disruption

Table 2. Relative Contraindications To Cricothyrotomy Age <10 y undesirable and <5 y should be avoided completely

Airway edema

Preexisting laryngeal pathology: epiglottitis, chronic inflammation, cancer

Mass (tumor, hematoma, abscess)

Anatomic barriers: stab wounds, hematoma

Supraglottitis

Coagulopathy

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Figure 1.

The Melker cricothyrotomy kit.

Figure 4.

The Portex kit.

in diameter that cross the midline. In patients for whom the landmarks are difficult to identify, a rule of thumb is that the membrane usually lies 4 fingerbreadths from the sternal notch.

Figure 2.

Figure 3.

Techniques

The Pertrach kit.

The QuickTrach kit.

The choice of technique for emergency access includes needle cricothyrotomy with high-flow oxygen, surgical cricothyrotomy (open or percutaneous Seldinger technique7), and transtracheal jet ventilation. Which method to use ultimately will be dictated by the physician’s experience and training with a particular technique. For the purposes of this review, only percutaneous cricothyrotomy using the Seldinger technique will be fully described. A variety of airway kits is available. These include the Melker (Cook; Figure 1), Pertrach (Pulmodyne; Figure 2), QuickTrach (VBM Medizintechnik; Figure 3), and Portex (Smiths Medical; Figure 4) cricothyrotomy kits. Each of these kits contains detailed instructions for proper use. However, the fundamental approach is essentially the same for all such devices. • Be sure the cricothyrotomy procedure will effectively bypass an obstruction if present. If the obstruction is within the distal trachea (foreign body, tumor), cricothyrotomy will be pointless.

Any clinician who performs intubations must know and review the structures of the neck, especially the support structures of the airway (thyroid cartilage, cricoid cartilage, and tracheal rings). The vocal cords are located a short distance (approximately 0.7 cm) above the thyroid notch. An attempt to place a surgical airway here would be harmful, as well as nearly impossible. The cricoid cartilage is a complete cartilaginous ring that can be felt in some individuals. The cricothyroid membrane has a vertical height of 8 to 19 mm and a width of 9 to 19 mm. It is located between the thyroid and cricoid cartilages.6 Branches of the thyroid arteries pierce the membrane in its upper third—thus, if possible, cutting the membrane in its lower third is desirable. Identifying the midline of the structure is important, as roughly 30% of the population has large-caliber veins within 1 cm of the midline, whereas only 10% have veins larger than 2 mm

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Table 3. Immediate and Delayed Complications Due to Cricothyrotomy: Elective and Emergent Immediate

Delayed

Hemorrhage into large neck vessel

Tracheal stenosis/ Tracheomalacia

Insertion into wrong tissue space

Bleeding

Right mainstem bronchus insertion

Infection/Mediastinitis

Esophageal intubation or trauma

Fistulae

Laceration of thyroid

Displacement

Injury to larynx and/or vocal cords Mediastinal emphysema Hypoxia and death

Scarring

• Use tools that are provided by the institution and/or the technique that you are most comfortable with. For the Seldinger approach, choose an appropriately sized cannula and determine whether or not it should be cuffed (cuffs allow for better ventilation and should be used whenever possible). • Assess the adequacy of neck exposure and whether neck extension is permissible. For example, in a morbidly obese patient with difficult landmarks, an open cricothyrotomy approach may be more hazardous than a needle cricothyrotomy. Some percutaneous kits encourage hyperextension of the neck to bring the trachea closer to the surface. This movement may, however, be contraindicated in some patients. If neck extension is not permitted, consider tracheostomy, as some neck extension is necessary to align the head with the long axis of the body before cricothyrotomy. • An understanding of the relevant anatomy is essential. The principles of performing an emergency cricothyrotomy remain the same in the child (under the age of 10-12 years), with a few caveats: Everything will be smaller, landmarks will be harder to find, and the chance of injuring an adjacent structure is greater. Rather than

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an incision, in children a 14- to 16-gauge needle should be inserted through the membrane. Transtracheal ventilation may be attempted. (QuickTrach kits are available for neonates to adults. They contain a needle and do not require an incision for insertion.)

‘Poor Man’s’ Cricothyrotomy With Low-Pressure, High-Flow Oxygen8 Occasionally, an emergent cricothyrotomy must be performed, but a prepackaged device cannot be readily located. When only a “nonsafety” angiocatheter and an adapter from a size 7.5 ETT are available, this technique may allow oxygen to reach the patient while a more stable option is considered. Angiocatheters are suitable for attaching syringes for aspiration of air for confirming entry into the trachea, and for attaching the adapter from a 7.5 ETT for high-flow oxygen delivery. Oxygen can be administered by replacing the 3-mL syringe with a 10-mL syringe. Remove the plunger. Place a 7-mL ETT into the 10-mL plunger, inflate the cuff, and attach the oxygen line to the adapter end of the ETT. This procedure does not produce a definitive airway and thus may only provide an additional 10 minutes of oxygenation. Furthermore, if an obstruction to exhalation is present, a second angiocatheter to release built-up carbon dioxide may be placed. Urgent surgical consultation is a must. A needle cricothyrotomy is only a temporary airway until a more stable airway—which may include intubation by a more experienced operator, full surgical cricothyrotomy, or regular tracheotomy —may be obtained. Even a small partial airway may be enough to keep a patient alive and avoid hypoxic brain damage until additional help can be mobilized.

Complications The cricothyroid membrane is superficial and easily accessible with minimal dissection, yet the procedure is not without disadvantages. The cricothyroid membrane is small and surrounded by adjacent structures—including the conus elasticus, cricothyroid muscles, and central cricothyroid arteries—that are easily injured (Table 3). Damage also may occur to the cricoid cartilage from a scalpel, resulting in perichondritis and stenosis. Immediate complications include damage to the thyroid cartilage and vocal cords, subcutaneous emphysema, hemorrhage, extratracheal tube placement, pneumothorax, laceration of the esophagus or trachea, and anoxia from prolonged placement time. Delayed complications include infection, fistulae, and damage to the larynx.

Case Study When the airway must be secured and time is not severely limited, percutaneous cricothyrotomy with the Seldinger technique may be preferable to percutaneous tracheotomy for those unfamiliar with the latter procedure. In this case, a 60-year-old man who had undergone 3-vessel cardiopulmonary bypass surgery was extubated 2 days postoperatively, but was reintubated without difficulty shortly afterward because of unexplained tachypnea, tachycardia, and agitation. Bacterial pneumonia was diagnosed and he remained hospitalized for an additional 7 days. Following a trial of extubation, he became tachypneic and severely agitated within 30 minutes and required reintubation. A grade 3 view

was seen with direct laryngoscopy following sedation and full paralysis. Despite the use of the GlideScope (Verathon Medical), significant airway edema prevented visualization of the vocal cords. An LMA ProSeal #5 (Teleflex) was inserted and ventilation was possible. Oxygen saturation improved from the mid 80s to low 90s. A decision was made to secure the airway via a surgical approach, and a percutaneous tracheostomy was attempted by the surgical team. However, despite multiple attempts, a false passage was created and ventilation and oxygenation was never achieved. The patient became more difficult to ventilate via the laryngeal mask airway and cardiopulmonary arrest ensued. The patient could not be resuscitated.

Conclusion

References

An elective cricothyrotomy carries a complication rate of 6%; for an emergent procedure, the rate approaches 40%, more than a 5-fold greater risk. Nonetheless, in the emergent setting, cricothyrotomy may be easier to perform than tracheostomy for many nonsurgical specialists, and a clinician can perform the procedure with few material resources. Prepackaged sterile percutaneous cricothyrotomy kits are available, and familiarity with a particular kit will increase the success of performing the procedure in little time under a great amount of pressure.

Authors’ note: As an anesthesia provider (JS), I do not find that fixing the neck from the patient’s right side is comfortable as is recommended from the cephalad position. When I teach this procedure, I frequently stand at the patient’s left side (I am right-handed) and fix the neck with my nondominant hand, but from the caudal area below the incision. Doing so allows the dominant right hand to perform the initial needlestick into the neck, which is caudally directed. However, if a neck incision is made initially, it may be preferable to stand on the right side.

6. Bennett JD, Guha SC, Sankar AB. Cricothyrotomy: the anatomical basis. J R Coll Surg Edinb. 1996;41(1):57-60.

Pahor, AL. Ear, nose and throat in ancient Egypt. Part III. J Laryngol Otol. 1992;106(10):863-873.

2. Brantigan CO, Grow JB Sr. Cricothyrotomy: elective use in respiratory problems requiring tracheotomy. J Thorac Cardiovasc Surg. 1976;71(1):72-81. 3. DeLaurier GA, Hawkins ML, Treat RC, et al. Acute airway management. Role of cricothyroidotomy. Am Surg. 1990; 56(1):12-15. 4. ASA Task Force on Management of the Difficult Airway. Practice guidelines for management of the difficult airway. Anesthesiology. 1993;78(3):597-602. 5. Bair AE, Panacek EA, Wisner DH, et al. Cricothyrotomy: a 5-year experience at one institution. J Emerg Med. 2003;24(2):151-156.

7. Melker JS, Gabrielli A. Melker cricothyrotomy kit: an alternative to the surgical technique. Ann Otol Rhinol Laryngol. 2005;114(7):525-529. 8. Brock G, Gurekas V. The occasional poor man’s cricothyrotomy. Can J Rural Med. 1999;4(3):149-151.

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Additional Reading 1.

Benkhadra M, Lenfant F, Nemetz W, et al. A comparison of two emergency cricothyroidotomy kits in human cadavers. Anesth Analg. 2008;106(1):182-185.

Berkow LC, Greenberg RS, Kan KH, et al. Need for emergency surgical airway reduced by a comprehensive difficult airway program. Anesth Analg. 2009;109(6):1860-1869.

Davis DP, Bramwell KJ, Hamilton RS, et al. Safety and efficacy of the Rapid Four-Step Technique for cricothyrotomy using a Bair Claw. J Emerg Med. 2000;19(2):125-129.

Hagberg CA (Ed). Handbook of Difficult Airway Management. Philadelphia, PA: Churchill Livingstone; 2000.

Helm M, Gries A, Mutzbauer T. Surgical approach in difficult airway management. Best Pract Res Clin Anaesth. 2005;19(4):623-640.

Koppel JN, Reed AP. Formal instruction in difficult airway management. A survey of anesthesiology residency programs. Anesthesiology. 1995;83(6):1343-1346.

Mariappa V, Stachowski E, Balik M, Clark P, Nayyar V. Cricothyroidotomy: comparison of three different techniques on a porcine airway. Anaesth Intensive Care. 2009;37(6):961-967.

Mayo PH, Hackney JE, Mueck JT, et al. Achieving house staff competence in emergency airway management: results of a teaching program using a computerized patient simulator. Crit Care Med. 2004;32(12):2422-2427.

Metterlein T, Frommer M, Ginzkey C, et al. A randomized trial comparing two cuffed emergency cricothyrotomy devices using a wire-guided and a catheter-over-needle technique. J Emerg Med. 2011;41(3):326-332.

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10.

Murphy C, Rooney SJ, Maharaj CH, et al. Comparison of three cuffed emergency percutaneous cricothyroidotomy devices to conventional surgical cricothyroidotomy in a porcine model. Br J Anaesth. 2011;106(1):57-64.

11.

Newgard CD, Koprowicz K, Wang H, et al. ROC Investigators. Variation in the type, rate, and selection of patients for out-ofhospital airway procedures among injured children and adults. Acad Emerg Med. 2009;16(12):1269-1276.

12.

Pettineo CM, Vozenilek JA, Wang E, et al. Simulated emergency department procedures with minimal monetary investment: cricothyrotomy simulator. Simul Healthc. 2009;4(1):60-64.

13.

Schober P, Hegemann MC, Schwarte LA, et al. Emergency cricothyrotomyâ&#x20AC;&#x201D;a comparative study of different techniques in human cadavers. Resuscitation. 2009;80(2):204-209.

14.

Stephens CT, Kahntroff S, Dutton RP. The success of emergency endotracheal intubation in trauma patients: a 10-year experience at a major adult trauma referral center. Anesth Analg. 2009;109(3):866-872.

15.

Vadodaria BS, Gandhi SD, McIndoe AK. Comparison of four different emergency airway access equipment sets on a human patient simulator. Anaesthesia. 2004;59(1):73â&#x20AC;&#x201C;79.

16.

Wong DT, Prabhu AJ, Coloma M, et al. What is the minimum training required for successful cricothyroidotomy? A study in mannequins. Anesthesiology. 2003;98(2):349-353.

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The Congenital Difficult Airway In Pediatrics CHERYL K. GOODEN, MD Associate Professor of Anesthesiology and Pediatrics Icahn School of Medicine at Mount Sinai Mount Sinai Medical Center New York, New York Dr. Gooden reports no relevant financial conflicts of interest.

he etiology of the difficult

airway (DA) in the pediatric patient may be a congenital

syndrome or an acquired defect. The majority of DAs in these 2 groups of patients can be identified before the induction of anesthesia. That said, the basis for predicting a DA in a child is somewhat limited.1

First, it is important to have an understanding of which characteristics of the normal pediatric airway may result in DA management. Second, clinicians should be cognizant of the key features of the congenital syndrome, particularly as they relate to overall airway management. Finally, congenital syndromes with a DA presentation necessitate an increase in the level of preparedness by the anesthesiologist. The airway management of a pediatric patient can present various challenges, even for the most experienced anesthesiologist. There are several anatomic differences between the neonate, infant and child airway and the adult airway.2 A thorough understanding of these differences is critical to ensure safe management of the pediatric airway. Several of these anatomic differences are summarized in Table 1. A number of physiologic differences exist between pediatric (in particular, neonate and infant) and adult airways. A detailed discussion of lung mechanics and function is beyond the scope of this article. However, it is important to note that there are differences in chest

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wall compliance, oxygen consumption, and composition of muscle fibers of the diaphragm that result in a greater incidence of airway resistance in neonates and infants. Ultimately, an increase in airway resistance causes an increase in the work of breathing that will lead to hypoventilation, hypoxemia and hypercapnia. Based on the various anatomic and physiologic differences in the airway, particularly in the neonate and infant, it would appear that pediatric patients are at a higher risk for an adverse airway event than adult patients. The Closed Claims database revealed that respiratory events were observed more frequently in the pediatric population than in adults.5 An additional layer of airway complexity exists with a congenital syndrome associated with DA. It is impossible to discuss all of the syndromes that present a DA as one of its features. This article will review some of the more commonly encountered congenital syndromes.

Selected Pediatric Congenital Syndromes APERT SYNDROME Apert syndrome is an autosomal dominant disorder caused by fibroblast growth factor receptor-2 (FGFR2) gene mutations. It is characterized by midfacial hypoplasia, craniosynostosis, a high-arched and narrow palate with or without a cleft, high forehead, flat occiput, and syndactyly. Occasionally, there may be choanal stenosis or atresia and cervical spine fusion. Intellectual and developmental disabilities may be present. The upper airway difficulties occurring in this disorder are primarily due to the small nasopharynx, reduced patency of the choanae, and anomalies of tracheal cartilage. The presence of abnormal tracheal cartilage increases the risk for injury during suctioning and reduces the ability to clear secretions.6

Table 1. Neonate/Infant/Child Airway Differences Compared With Adult Airway Head (occiput)

Relatively large

Nares

Small

Neck

Short

Tongue

Large relative to mouth size

Larynx

More cephalad in the infant at C2 until it approaches that of the adult at C4

Epiglottis

Long and angled, projecting above the glottic opening

Vocal cords

Slanted anteriorly and rostrally

Narrowest part

Recent studies suggest the glottis instead of the larynx cricoids cartilage3,4

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BECKWITH-WIEDEMANN SYNDROME Most cases of Beckwith-Wiedemann syndrome are sporadic. Whereas other cases are known to be inherited in an autosomal dominant fashion, this disorder is caused by the insulin-like growth factor-2 (IGF-2) gene, which plays a role in somatic overgrowth. Beckwith-Wiedemann syndrome consists of macroglossia, macrosomia, omphalocele, visceromegaly, and exophthalmos. Additional features of this syndrome include malocclusion with mandibular prognathism and maxillary underdevelopment. The macroglossia can lead to upper airway obstruction, especially during the induction phase of anesthesia. These children can benefit from lying on their side or face down to improve respiration. In more severe cases, a partial glossectomy may be beneficial.7

CROUZON SYNDROME Crouzon syndrome, similar to Apert syndrome, is inherited in an autosomal dominant manner. Also like Apert syndrome, this craniofacial dysmorphic disorder results from FGFR2 gene mutations. However, different mutations are responsible for Crouzon syndrome. The anomalies found in Crouzon syndrome are limited to the craniofacial region, and include premature craniosynostosis of the coronal, sagittal, and lambdoid sutures. Maxillary hypoplasia, hypertelorism and shallow orbits are present. Occasionally, these patients have cleft lip and palate and tracheobronchomalacia. There have been reports of tracheal cartilaginous sleeves.8 Hearing loss is present. Upper airway obstruction is commonly manifested as obstructive sleep apnea, but acute respiratory distress is not often observed.

DOWN SYNDROME Typical airway findings in patients with Down syndrome include macroglossia, pharyngeal muscle hypotonia, narrowed nasopharynx, short neck, high-arched palate, and lax cervical vertebral ligaments. Adenoidal and tonsillar hypertrophy may be present. It is not unusual for children with Down syndrome to require a smaller than predicted endotracheal tube size because their trachea may be small.9 The presence of a large protuberant tongue and pharyngeal muscle hypotonia also put these patients at increased risk for difficult intubation and postoperative airway obstruction. One possible solution for postoperative respiratory complications is administration of nasal continuous positive airway pressure to maintain airway patency.10

GOLDENHAR SYNDROME Most cases of Goldenhar syndrome are sporadic, but some inheritance may be autosomal dominant or autosomal recessive. Many of the features that are observed in Goldenhar syndrome are the result of anomalies of the first and second branchial arches, and primarily the result of a vascular accident in utero. Goldenhar syndrome involves hypoplasia of the malar, maxillary, and mandibular regions. In addition, hypoplasia of facial musculature,

lateral cleft-like extension of the corner of the mouth, anomalies of the tongue, microtia, and occasionally cleft lip and palate may be present. Cervical spine and temporomandibular joint fusion also have been reported.1 These anomalies collectively can result in restricted mouth opening, limitation of neck flexion and extension, and poor mask seal due to asymmetry, all of which progressively worsen with age.

KLIPPEL-FEIL SEQUENCE The majority of cases of Klippel-Feil sequence are sporadic, but some inheritance is autosomal dominant. Some features of Klippel-Feil sequence include a short neck, limited head movement, and a low hairline, and the syndrome may be primarily the result of intrauterine disruption of the subclavian or vertebral arteries and failure of normal segmentation of the cervical spine.11 The airway can be managed by mask fairly easily, but intubation remains difficult due to limitation of neck movement.

PFEIFFER SYNDROME Pfeiffer syndrome consists of 3 clinical subtypes. Type

1 is an autosomal dominant disorder, whereas types 2 and 3 occur sporadically. The majority of cases are the result of mutations in the genes that encode FGFR1 or FGFR2. The main features of Pfeiffer syndrome are craniosynostosis, mild syndactyly, and broad thumbs and great toes. In addition, maxillary hypoplasia, proptosis, and shallow orbits are present. Occasionally, laryngomalacia, tracheomalacia, and bronchomalacia may be observed. Vertebral fusion can occur, usually of the upper cervical spine, which may limit mobility and make laryngoscopy more difficult. Patients with Pfeiffer syndrome, similar to those with Crouzon syndrome, can have a tracheal cartilaginous sleeve.12

PIERRE ROBIN SEQUENCE The classic features of Pierre Robin sequence include micrognathia, glossoptosis, and cleft soft palate that have long been known to complicate intubation in affected children.13 Hypoplasia of the mandible occurs before 9 weeksâ&#x20AC;&#x2122; gestation, causing the tongue to be posteriorly displaced. Mechanical constraint in utero also has been proposed as a possible mechanism. Neuromuscular

Table 2. Clinical Features of Selected Congenital Syndromesa Autosomal Dominant Inheritance Apert syndrome

BeckwithWiedemann syndrome

+/sporadic

Crouzon syndrome

Cervical Spine Fusion

Craniosyn- Cleft ostosis Palate

Hearing HighMacroLoss arched glossia Palate

Micrognathia

Obstructive Sleep Apnea +

Down syndrome

Goldenhar syndrome

+/sporadic, recessive

Klippel-Feil sequence

+/sporadic

Pfeiffer syndrome

+/sporadic

Pierre Robin sequence

Treacher Col- + lins syndrome

Highlighted clinical features may not always be present

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dysfunction of lingual and pharyngeal musculature is another manifestation of this disorder. In some patients with Pierre Robin sequence, intubation becomes less difficult with increasing age due to catch-up mandibular growth, but in others the mandible remains proportionately small. For anesthetic management, these patients may require prone positioning, a nasopharyngeal airway, or glossolabiopexy.

TREACHER COLLINS SYNDROME Treacher Collins syndrome is an autosomal dominant disorder and most likely involves a gene (TCOF1) that encodes a protein involved in embryonic craniofacial development. The main features of this disorder include malar hypoplasia with down-slanting palpebral fissures, zygomatic hypoplasia, mandibular hypoplasia, malformation of the external ear, and lower eyelid colobomas. A small mouth opening, high-arched palate, cleft lip or palate, and pharyngeal hypoplasia also may be present. Mask ventilation and intubation can be nearly impossible to perform. The procedure of choice in the past has been either sedated fiber-optic intubation or placement of a supraglottic airway.13

Conclusion Airway management of the pediatric patient with a syndrome associated with DA is an ongoing challenge for the anesthesiologist. The skill set required in the airway-related care of these patients is similar to that for any pediatric patient with DA. However, an understanding of the unique clinical features of these syndromes remains crucial to the anesthesia care (Table 2).

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References 1.

Frei F, Ummenhofer W. Difficult intubation in paediatrics. Pediatr Anesth. 1996;6(4):251-263.

2. Infosino A. Pediatric upper airway and congenital anomalies. Anesthesiology Clin N Am. 2002;20:747-766. 3. Litman R, Weissend E, Shibata D, et al. Developmental changes of laryngeal dimensions in unparalyzed, sedated children. Anesthesiology. 2003;98(1):41-45. 4. Dalal P, Murray D, Messner A, et al. Pediatric laryngeal dimensions: an age-based analysis. Anesth Analg. 2009;108(5):1475-1479. 5. Morray J, Geiduschek J, Caplan R, et al. A comparison of pediatric and adult anesthesia closed malpractice claims. Anesthesiology. 1993;78(3):461-467. 6. Basar H, Buyukkocak U, Kaymak C, et al. An intraoperative unexpected respiratory problem in a patient with Apert syndrome. Minerva Anestesiol. 2007;73(11):603-606. 7. Wang J, Goodger N, Pogrel M. The role of tongue reduction. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2003;95(3):269-273. 8. Scheid S, Spector A, Luft J. Tracheal cartilaginous sleeve in Crouzon syndrome. Int J Pediatr Otorhinolaryngol. 2002;65(2):147-152. 9. Shott S. Down syndrome: analysis of airway size and a guide for appropriate intubation. Laryngoscope. 2000;110(4):585-592. 10. Ito H, Sobuek, So M, et al. Postextubation airway management with nasal continuous positive airway pressure in a child with Down syndrome. J Anesth. 1996;6:251-263. 11. Issaivanan M, Virdi V, Parmar V. Subclavian artery supply disruption sequenceâ&#x20AC;&#x201D;Klippel-Feil and Mobius anomalies. Indian J Pediatr. 2002;69(5):441-442. 12. Hockstein N, McDonald-McGinn D, Zackai E, et al. Tracheal anomalies in Pfeiffer syndrome. Arch Otolaryngol Head Neck Surg. 2004;130(11):1298-1302. 13. Nargozian C. The airway in patients with craniofacial abnormalities. Pediatr Anesth. 2004;14(1):53-59.

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Supraglottic Airways As Bridges to Safe Extubation Of the Difficult Airway PHILLIP G. SCHMID III, MD Assistant Professor, Department of Anesthesiology Medical College of Wisconsin Milwaukee, Wisconsin

MOHAMMAD EL-ORBANY, MD Professor, Department of Anesthesiology Medical College of Wisconsin Milwaukee, Wisconsin

The authors report no relevant financial conflicts of interest.

ifficult airway management (DAM) does not end with successful tracheal intubation (TI). In fact, the adoption of established DAM guidelines and

the availability of numerous advanced airway management devices have

significantly reduced the incidence of patient injury occurring during TI.1

According to analyses of the American Society of Anesthesiologists’ (ASA) Closed Claims database, although airway-related patient injury including brain death and mortality occurring during TI has decreased substantially, it remains unchanged for all other phases of anesthesia management, including the immediate period after extubation.2 Data from the United Kingdom show similar trends. The fourth National Audit Project (NAP4) of the Royal College of Anaesthetists and the Difficult Airway Society (DAS) in the United Kingdom reported that major airway complications occur during emergence and recovery from anesthesia in approximately one-third of all adverse events related to anesthesia.3 These data highlight the fact that tracheal extubation (TE) and the immediate postextubation period are among the most challenging phases of anesthesia management. Clinicians should plan carefully for these phases, particularly in patients with difficult airways or with limited airway access. To address this issue, the ASA Task Force on Management of the Difficult Airway has recently recommended a staged extubation strategy when uncertainty exists

regarding the ability of the patient to maintain adequate ventilation after TE.4 The short-term use of an airway device that can serve as a guide for expedited reintubation, if needed, should be considered in patients at risk for failed extubation. The use of such a “bridging” device can confer reversibility to the extubation process and allow tracheal reintubation in a timely manner. Ideally, the device should be placed before TE. The endotracheal tube (ETT) is then removed and the device remains in place until it can be withdrawn safely. The guidelines recommend the use of either an airway stylet/catheter or a supraglottic conduit for bridging.4 The DAS also has published its recommendations and guidelines for the management of TE with descriptions of the use of some of these bridging devices.5

Extubation Failure Extubation failure has been defined as the inability to maintain adequate ventilation after removal of the ETT.6 The underlying mechanisms are airway obstruction, hypoventilation, inability to clear secretions or protect the airway, or airway trauma during TI or surgery. The

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management of extubation failure is reintubation. Table 1 summarizes some of the causes of extubation failure. It should not be confused with “weaning failure,” which is a totally different clinical entity that entails failure to maintain adequate spontaneous ventilation without mechanical ventilatory assistance and can be managed either by invasive or noninvasive ventilatory support.6 Although the focus of extubation failure should be on the ETT as the therapeutic measure, in weaning failure the focus should be on the ventilator.

AIRWAY RISK FACTORS OF EXTUBATION RISK

AND

STRATIFICATION

The ability to recognize situations of high-risk extubation is probably the most crucial step in preventing mishaps related to TE. Although no study has investigated extubation risk factors or the correlation between each factor and the incidence of reintubation, anecdotal data and case reports provide helpful tools to the practitioner to identify and stratify patients into 3 broad groups.7 The low-risk extubation group consists of nonobese patients with negative history of difficult intubation or sleep apnea, whose airway exam is normal, and who are scheduled for a non-airway, head, or neck surgery. Routine TE can be performed safely in these patients. The intermediate-risk group includes patients in whom there is uncertainty regarding the ability to tolerate extubation, but in whom reintubation is not expected to be problematic and can be easily performed when needed. Examples are patients with vocal cord dysfunction, such as paradoxical vocal cord motion, mild degrees of tracheomalacia, airway granulomas and sarcoid masses, and pharyngeal muscle dysfunction, such as parkinsonism with normal upper airway exam. Although airway obstruction can occur in those patients after TE, mask ventilation and/or reintubation are expected to proceed uneventfully. The high-risk extubation group comprises patients in whom there is uncertainty regarding the ability to tolerate extubation and it is almost certain that mask ventilation and/or reintubation can be difficult if needed (Table 2).3 In each of these groups, the assumption is that the decision has been made that TE can be performed safely or is desirable. Because TE is an elective procedure, a decision must be made in each individual case whether it is safe to remove the ETT or to keep the trachea intubated for a certain period of time postoperatively until extubation conditions are more favorable. We would like to add a fourth group to these classifications. It includes patients who most likely will fail extubation, those for whom reintubation can be extremely difficult or impossible, those who cannot tolerate even brief periods of hypoventilation, those for whom extubation conditions are expected eventually to improve, and patients with no clear indication for immediate extubation. The approach for patients in this group should be to postpone TE until the conditions improve and it can be performed safely. Evidently, the most challenging patients are those in

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Table 1. Causes of Extubation Failure8 Airway Obstruction Anterior cervical decompression Maxillofacial trauma Neck hematoma No cuff leak Obstructive sleep apnea Paradoxical vocal cord motion Post-thyroidectomy Post–carotid endarterectomy Post-panendoscopy Post-uvulopalatopharyngoplasty Recurrent laryngeal nerve palsy Tracheomalacia Hypoventilation syndromes Central sleep apnea Diaphragmatic splinting Excess carbon dioxide production Preexisting neuromuscular disorder Residual anesthetic or muscle relaxant effects Severe chronic obstructive pulmonary disease Hypoxemic respiratory failure Decreased oxygen delivery Impaired pulmonary diffusion Inadequate inspired oxygen concentration Increased oxygen consumption Right-to-left shunt Ventilation/perfusion mismatch Pulmonary toilet Neuromuscular impairment Obtundation Pulmonary secretions Inability to protect airway Decreased level of consciousness Neuromuscular weakness

group 3, as they are most likely to experience rapid deterioration after extubation—and poor planning and preparation may lead to a high rate of morbidity and mortality. It is also the group for whom the revised ASA guidelines recommend the use of a well-planned extubation strategy with the aid of some airway devices as discussed here.

Table 2. Examples of High-Risk Extubation Conditions Airway burns, neck flexion deformity or scar, irradiation Anterior and posterior cervical spine surgery

Extubation Strategies and Devices For Bridging

Burn patients with smoke inhalation injury Carotid endarterectomy Certain surgical procedures Cervical spine immobilization (halo vest) Diaphragmatic splinting Documented previous difficulty with mask ventilation and/or tracheal intubation Extensive neck dissection General medical conditions Guardian suture fixing chin to chest after tracheal resection Intermaxillary fixation and wiring Limited airway access Maxillofacial surgery Multiple attempts at tracheal intubation and/or use of alternative airway devices and techniques for intubation at start of surgery

ETT EXCHANGER

Obstructive sleep apnea Parkinsonism Pharyngeal, laryngeal, or tracheal trauma during intubation (eg, arytenoid dislocation, vocal cord avulsion, laryngeal edema) Posterior fossa surgery Previous or current airway difficulty Rheumatoid arthritis Submandibular, submental, retro- and parapharyngeal infections Thyroid surgery Tracheal resection Tracheomalacia Vocal cord and laryngoscopic surgery Vocal cord dysfunction (paradoxical vocal cord motion) Uvulopalatopharyngoplasty

No single device or technique works in every situation. The decision to use a specific device should be based on the specific case scenario and the familiarity and expertise of the managing anesthesiologist. With this in mind, the device that should be considered as a bridge to safe extubation of the difficult airway should accomplish the following: • Allow patient oxygenation and ventilation until the airway is no longer at risk • Assist in accomplishing expedited reintubation, if required, after TE • Allow uninterrupted airway access • Not interfere with patient comfort or cause further complications The ASA task force has recommended the consideration of either an ETT exchanger or stylet and/or a supraglottic airway (SGA) as bridges for safe extubation of the high-risk airway.4 OR

STYLET

A wide variety of airway exchange catheters and tracheal tube introducers are commercially available and can be used for this purpose. Examples include Eschmann introducers (SunMed), Frova intubating introducers (Cook Medical Inc.), Cook airway exchange catheters (AECs), Arndt AECs (Cook Medical Inc.), endotracheal ventilation catheters (CardioMed), and Aintree catheters (Cook Medical Inc.). Each of these devices has external depth markings and can be passed through the existing ETT to a predetermined depth. The ETT is then removed and the catheter or stylet is fixed and left in place until it can be removed safely. Hollow catheters are preferable to solid ones, as they permit oxygen insufflation or ventilation.8 Their use for insufflation or ventilation, however, may result in fatal complications and therefore recently has been discouraged except as a last resort.9 If reintubation is deemed necessary, the new ETT can be railroaded over the catheter. The reported success of reintubation with the use of these catheters in failed exubation situations in a difficult airway, or in an airway with limited access, had made their use popular.10 However, complications may limit their use in favor of other devices that can be used safely for ventilation.

SUPRAGLOTTIC AIRWAY DEVICES Certain SGAs can serve as bridges to safe extubation of the difficult airway by allowing uninterrupted airway access, providing oxygenation and ventilation, and

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serving as conduits for reintubation. They can be used alone or in combination with AECs and/or a fiber-optic bronchoscope (Figures 1-8). Not all SGAs can be used as extubation bridges, however. The best supraglottic extubation bridge is one designed to function as an intubation conduit in addition to a stand-alone airway device.11 From the limited available literature and our experience, the following devices fit best in this role: The LMA Classic or LMA Unique (Teleflex), Intubating LMA (LMA Fastrach, Teleflex), and the air-Q (Mercury Medical). These SGAs have wide ventilatory tubes that can accommodate a 7.0 internal diameter ETT. They can be railroaded over the existing ETT or placed behind it. They also can be railroaded into position over an existing stylet or exchange catheter, and they allow fiber-optic examination of the airway. Ellard et al reported using an LMA Classic as an extubation bridge after thyroidectomy and tracheal resection in a 75-year-old man who underwent awake TI

before anesthesia induction.12 Extubation was desirable to avoid the effects of positive pressure ventilation on the tracheal repair. The LMA provided a route for fiberoptic examination of vocal cord functions. Komasawa et al reported using an air-Q and a tube exchanger as extubation bridges after total maxillectomy in a 79-year-old man.13 The authors inserted the exchanger through the ETT, removed the ETT, then railroaded the SGA over the exchanger. Raveendran et al used an LMA ProSeal and an exchange catheter as extubation bridges after thyroidectomy in a patient who had difficult intubation.14

Conclusion The role of SGAs as extubation bridges in the management of the difficult airway is evolving. The accompanying case scenarios highlight the vital role of the SGAs when used as bridges to safe extubation for high-risk situations.

Figure 1.

Supraglottic airway placed behind the endotracheal tube before tracheal extubation.

Figure 3.

If reintubation is needed, fiberoptic-aided intubation can be swiftly performed through the supraglottic airway.

Figure 2.

Fiber-optic examination of the periglottic area, vocal cords, and trachea through the supraglottic airway.

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Figure 4.

Fiberoptic-aided tracheal reintubation using the air-Q as a conduit.

The anesthesiologist should have a preformulated extubation strategy for the difficult airway and the patient at high risk for extubation. Detection of general and airway risk factors is crucial for stratification of extubation risk and avoidance of postextubation mishaps. The short-term use of a bridging device should be considered for its ability to provide reversibility to the extubation process. Either an airway stylet or catheter, or a supraglottic conduit, can serve this purpose and allow

continuous access to the airway after TE. Familiarity with these devices and prior knowledge of their use and limitations is mandatory for patient safety.

References 1. 2.

Cavallone LF, Vannucci A. Review article: extubation of the difficult airway and extubation failure. Anesth Analg. 2013;116(2):368-383. Peterson GN, Domino KB, Caplan RA, et al. Management of the difficult airway: a closed claims analysis. Anesthesiology. 2005;103(1):33-39. Cook TM, Woodhall N, Frerk C; Fourth National Audit Project. Major complications of airway management in the UK: results of the Fourth National Audit Project of the Royal College of Anaesthetists and the Difficult Airway Society. Part 1: anaesthesia. Br J Anaesth. 2011;106:617-631. Apfelbaum JL, Hagberg CA, Caplan RA, et al. Practice guidelines for management of the difficult airway. An updated report by the American Society of Anesthesiologists task force on management of the difficult airway. Anesthesiology. 2013;118(2):251-270. Difficult Airway Society Extubation Guidelines Group, Popat M, Mitchell V, Dravid R, et al. Difficult Airway Society guidelines for the management of tracheal extubation. Anaesthesia. 2012;67(3):318-340. references continued, page 66

Figure 5.

Supraglottic airway can be railroaded into position over an existing airway exchange catheter.

Figure 7.

If reintubation is needed, it can be performed through the supraglottic airway by railroading the endotracheal tube over the airway exchange catheter.

Figure 6.

A swivel adaptor is used to attach the supraglottic airway to a T-piece or a breathing circuit, while keeping the airway exchange catheter in place.

Figure 8.

Tracheal reintubation through an air-Q using the airway exchange catheter as a guide.

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Case Study 1 A 54-year-old woman was scheduled for a 3-level anterior cervical corpectomy and fusion. The patient had a history of upper extremity weakness and paresthesia resulting from pathology of her cervical spine that progressively worsened, particularly with neck movement. Awake orotracheal fiber-optic intubation was performed successfully and surgery proceeded. After the 5-hour procedure, a halo vest was placed. At the end of surgery, and with the patient breathing spontaneously, a cuff-leak test was performed that indicated adequate leak. An air-Q was placed behind the orotracheal tube and the trachea was extubated. The patient went to the postanesthesia care unit (PACU) awake, breathing spontaneously, and obeying simple commands with the air-Q in place. The SGA was connected to a T-Piece with oxygen flow of 6 L/minute. SpO2 remained above 97 for 10 minutes, after which it began declining over the next 10 minutes until it reached 90 with no improvement despite increasing the O2 flow rate. A stridorous sound

became audible with inspiration. A fiber-optic bronchoscope (FOB) was introduced through the air-Q, and examination of the vocal cords revealed bilateral partial adduction. Fiber-optic–aided reintubation was successfully completed in less than 20 seconds. Airway complications after anterior cervical surgery are well reported. An extubation bridge was planned due to the multilevel procedure that lasted for 5 hours. Recurrent laryngeal nerve injury occurs in 5% of patients who underwent multilevel anterior cervical surgery, causing postoperative respiratory compromise. In this case, cervical spine fusion, pharyngeal edema, and limited access to the airway because of the halo could have made reintubation impossible. The air-Q kept the airway patent during the immediate postoperative period, allowed an uninterrupted airway access, permitted examination of the vocal cords, and facilitated emergency reintubation when the patient’s ventilation was compromised.

Case Study 2 A 55-year-old woman presented with a huge thyroid mass and was scheduled for total thyroidectomy. Computed tomographic scans of the neck and upper chest revealed marked tracheal deviation and retrosternal extension. Awake orotracheal fiber-optic intubation was successfully performed and surgery proceeded. At the end of the procedure, TE was desirable. However, there was some uncertainty regarding left recurrent laryngeal nerve injury and whether the retrosternal tumor had resulted in tracheomalacia. An FOB within an Aintree catheter was advanced through the ETT until its tip emerged from the distal end of the ETT. Airway examination was performed while the ETT was slowly withdrawn after cuff deflation. Fiber-optic examination revealed no abnormalities of the trachea or vocal cords, and it was decided to perform TE but keep an LMA as an extubation bridge during her time in the PACU. The FOB was withdrawn, the catheter was advanced through the cords, and the ETT was removed. An LMA Unique was railroaded in place over the Aintree catheter and the latter was removed. Within 10 minutes, the patient’s oxygen saturation began to decrease

6. Epstein SK. Decision to extubate. Intensive Care Med. 2002;28(5):535-546. 7. Cooper RM. Extubation and changing endotracheal tubes. In: Hagberg CA, ed. Benumof’s Airway Management: Principles and Practice. Philadelphia, PA: Mosby; 2007:1164-1180. 8. Cooper RM. Safe extubation. Anesth Clin North America. 1995;13(3):683-707. 9. Duggan LV, Law JA, Murphy MF. Brief review: supplementing oxygen through an airway exchange catheter: efficacy, complications, and recommendations. Can J Anesth. 2011;58(6):560-568. 10. Mort TC. Continuous airway access for the difficult extubation: the efficacy of the airway exchange catheter. Anesth Analg. 2007;105(5):1357-1362.

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gradually, with increasing efforts at both inspiration and expiration. The FOB was introduced through the LMA, and re-examination revealed a collapsing upper tracheal wall—indicating mild tracheomalacia that probably was missed on the brief initial examination. Tracheomalacia became more evident with increasing inspiratory efforts and increasing the negative intrathoracic pressure. A decision was made to reintubate the trachea to stent open the upper tracheal segment. An ETT was advanced over the FOB and reintubation was successfully accomplished in less than 30 seconds. The FOB and LMA were withdrawn, and the trachea was kept intubated pending further consultation with the thoracic surgeon. In this case, the FOB allowed initial airway examination as well as reintubation, and the Aintree catheter allowed uninterrupted airway access during the exchange of the ETT and LMA. The LMA allowed access to the airway and served as a route for bronchoscopic examination, as well as a conduit when the decision to reintubate was made based on the examination findings.

11. El-Orbany M. The use of a supraglottic airway device as an extubation bridge for the difficult airway. Can J Anesth. 2014;61(4):387-388. 12. Ellard L, Brown DH, Wong DT. Extubation of a difficult airway after thyroidectomy: use of a flexible bronchoscope via the LMA-Classic. Can J Anesth. 2012;59(1):53-57. 13. Komasawa N, Ueki R, Iwasaki Y, et al. Use of the air-Q laryngeal airway and tube exchanger in a case of difficult tracheal extubation after maxillectomy. Masui. 2012;61(10):1125-1127. 14. Raveendran R, Sastry SG, Wong DT. Tracheal extubation with a laryngeal mask airway and exchange catheter in a patient with difficult airway. Can J Anesth. 2013;60(12):1278-1279.

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