By Vibhu Sharma, MD
Associate Professor of Medicine, University of Colorado, Denver
SYNOPSIS: The American Society of Anesthesiologists has released updated guidelines on the management of the difficult airway.
SOURCE: Apfelbaum JL, Hagberg CA, Connis RT, et al. 2022 American Society of Anesthesiologists Practice Guidelines for Management of the Difficult Airway. Anesthesiology 2022;136:31-81.
The difficult airway is defined as a “clinical situation in which anticipated or unanticipated difficulty or failure is experienced by a physician trained in anesthesia care, including but not limited to one or more of the following: facemask ventilation, laryngoscopy, ventilation using a supraglottic airway, tracheal intubation, extubation, or invasive airway.” The authors further specify that “these guidelines are intended for use by anesthesiologists and all other individuals who perform anesthesia care or airway management.”
Historical associations with a difficult airway include obesity, obstructive sleep apnea, and mediastinal masses. Tonsillar hypertrophy and tongue and supraglottic pathology similarly may predict difficult intubation or laryngoscopy. A previous history of difficult airway access is a strong predictor of current difficult airway access, and this history should be sought meticulously. Disorders of the cervical spine that limit flexion and extension also are associated with difficult airway access. Although there is a paucity of literature comparing multiple vs. single physical exam findings in predicting a difficult airway, findings suggesting difficulty with intubation include large incisors, marked overbite, inability to bring mandibular incisors anterior to maxillary incisors, Mallampati class > 2, high arched palate, stiff or indurated base of the tongue, a short and thick neck, a thyromental distance less than three finger-breadths, and inability to extend the neck or touch the chin to the chest. Ultrasound findings, such as increased skin-to-hyoid distance, tongue volume, and distance from skin to epiglottis, also are predictive.
Preoxygenation is the most important intervention to prevent desaturation related to airway access. Upright positioning (especially in obese patients) facilitates preoxygenation. Preoxygenation typically is provided with a facemask; however, in the event that facemask oxygenation proves difficult or impossible, laryngeal mask airways (LMAs) can provide rescue ventilation in up to 94% of patients. An LMA typically is placed after applying gel to the posterior aspect of the device and inserting it blindly into the hypopharynx with the head hyperextended. LMAs are not typically used in scenarios involving oropharyngeal mass lesions that cause an anticipated difficult airway.
Positioning a patient is important to improve laryngoscopic views, and the guidelines recommend maintaining the head and neck in a sniffing position to improve laryngeal visualization. Use of a backward-upward-rightward pressure (“BURP”) maneuver of the larynx and external cricoid manipulation both improve visualization of the larynx. Pre-induction transnasal endoscopic assessment of the glottis may help better predict Cormack-Lehane scores compared with pre-intubation clinical assessment alone.1 This technique may add to the precision of predicting glottic views with direct laryngoscopy.
The guidelines emphasize the need to be prepared for the difficult airway. Consider difficulty with patient consent for an agitated patient, difficulty with facemask ventilation due to facial deformities or a beard, difficulty with supraglottic device placement in the setting of a pharyngeal or hypopharyngeal mass, difficulty with intubation relating to supraglottic or laryngeal pathology (e.g., tumors, vocal cord paralysis, soiling of the upper airway), tracheal pathology due to tumors or stenosis, and, finally, difficulty with performance of a surgical airway in the setting of massive obesity, soft tissue masses of the anterior neck, or prior neck radiation. Evaluation of these potential difficulties in the sequence in which intubation occurs (patient > face > mouth > pharynx > hypopharynx > glottis > larynx > trachea > front of neck) is a helpful mnemonic.
A video laryngoscope typically is the preferred device for endotracheal intubation of the predicted difficult airway, whether done awake or with anesthesia/paralysis. Video laryngoscopy (VL) improves laryngeal view (odds ratio [OR], 5.3-7) and first-pass success rate of intubation (OR, 3) compared with direct laryngoscopy (DL) in simulated and predicted real-life scenarios of difficult airways.2 Time to intubation for VL compared with DL in simulated or predicted real-life scenarios of difficult airways was equivocal in meta-analyses of randomized trials. Although randomized controlled trials have been equivocal when comparing hyper-angulated VLs with non-hyper-angulated VLs, clinicians may prefer the use of hyper-angulated blades for patients with limited jaw or neck mobility, obstructive sleep apnea, and anterior airways. With respect to non-video laryngoscopes, laryngoscopes with flex tips (the “McCoy”/levering laryngoscopes) were associated with shorter times to intubation and fewer intubation attempts for successful intubation in patients with an initial poor laryngoscopic view.3
Flexible bronchoscopy and fiberoptic nasotracheal intubation have been used successfully after failed direct laryngoscopy and for unanticipated and emergency difficult airways. Although there are no randomized trials to assess the utility of an awake fiberoptic intubation strategy in the setting of a difficult airway, estimates from observational studies document 78% to 100% success rates. Use of an endotracheal tube loaded onto a bronchoscope with intubation through an intubating LMA (ILMA) has a higher rate of first-pass success than conventional fiberoptic bronchoscopy alone.4 One intriguing study suggests that intubation may be quicker with better views of the glottis using a second-generation LMA (the i-gel) compared with an ILMA (Ctrach or Fastrach LMA).5 In this study, size 7.0 endotracheal tubes were used for size 4 i-gel LMAs and size 7.5 tubes for size 5 i-gel LMAs. The endotracheal tubes were loaded onto a bronchoscope and then “railroaded” into the trachea once the bronchoscope was introduced into the trachea through the i-gel device. Alternatively, a bronchoscope loaded into an Aintree tube exchanger may be introduced through an LMA to allow for accurate placement of the tube exchanger into the trachea, followed by “railroading” an endotracheal tube over the Aintree tube exchanger. One randomized controlled trial compared VL combined with a flexible bronchoscope to VL alone and found a greater first-attempt success rate with the combination.6
The major decision prior to intubating a predicted difficult airway remains whether to paralyze the patient (i.e., whether to use an awake intubation strategy). The guidelines recommend performing awake intubation if there is concern for a difficult intubation and if one or more of the following is present: difficult ventilation (facemask/supraglottic airway); increased risk of aspiration; inability of the patient to tolerate a brief apneic episode; or expected difficulty with emergency invasive airway rescue.
Once a decision has been made to perform either an awake intubation or proceed with ablation of ventilation with general anesthesia, it then is important to decide whether endotracheal intubation will proceed or if a surgical/percutaneous approach is needed. The latter will be necessary in the scenario of critical or near-critical obstruction of the upper airway because of scenarios such as severe angioedema, soft tissue swelling, tumor, or glottic stenosis. Any attempt at intubation in these situations may need to happen in the operating room with trained otolaryngologists ready to perform a surgical tracheostomy immediately if indicated. In the setting of an unanticipated difficult airway, the guideline document recommends calling for help, optimizing oxygenation, determining the benefit of restoring spontaneous breathing, and determining the benefit of a noninvasive vs. invasive approach to airway management. Combination techniques for rescue of the unanticipated difficult airway might include fiberoptic bronchoscopy-aided intubation using a conduit (i.e., LMA), fiberoptic bronchoscopy plus VL, or bougies/stylets. The success rates of various combination techniques are discussed in greater detail in the guideline document.
The guideline document delineates strategies for safe extubation of a difficult airway as well. Similar to pre-intubation of a difficult airway, potential anatomic difficulties should be considered. For the critical care clinician, use of a bougie or tube exchange catheter through which ventilation and oxygenation may be provided can be useful as a short-term strategy to assess whether extubation will succeed. Most patients tolerate these devices (with oxygen entrained) in their airways remarkably well. It is axiomatic that every difficult airway is unique. Clinicians should not only use their best judgment, but, most importantly, should know whom to call for help when needed.
REFERENCES
- Gemma M, Buratti L, Di Santo D, et al. Pre-operative transnasal endoscopy as a predictor of difficult airway: A prospective cohort study. Eur J Anaesthesiol 2020;37:98-104.
- 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;118:251-270.
- Beilin B, Yardeni IZ, Smolyarenko V, et al. Comparison of the Flexiblade levering laryngoscope with the English Macintosh laryngoscope in patients with a poor laryngoscopic view. Anaesthesia 2005;60:400-405.
- Langeron O, Semjen F, Bourgain JL, et al. Comparison of the intubating laryngeal mask airway with the fiberoptic intubation in anticipated difficult airway management. Anesthesiology 2001;94:968-972.
- Michálek P, Donaldson W, McAleavey F, et al. The i-gel supraglottic airway as a conduit for fibreoptic tracheal intubation — A randomized comparison with the single-use intubating laryngeal mask airway and CTrach laryngeal mask in patients with predicted difficult laryngoscopy. Prague Med Rep 2016;117:164-175.
- Mazzinari G, Rovira L, Henao L, et al. Effect of dynamic versus stylet-guided intubation on first-attempt success in difficult airways undergoing Glidescope laryngoscopy: A randomized controlled trial. Anesth Analg 2019;128:1264-1271.
The American Society of Anesthesiologists has released updated guidelines on the management of the difficult airway.
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