The definition of a difficult airway has remained nebulous despite ongoing international effort due to the complexity and variety of factors constituting this phenomenon. The latest practice guidelines by the American Society of Anesthesiologists (ASA) simply define a difficult airway as an airway that, to a conventionally trained provider, presents a challenge in terms of intubation, ventilation, or both.1 The reported incidence of a difficult airway in the literature varies. Difficult mask ventilation occurs in approximately 2% of cases, with impossible mask ventilation occurring in 0.15% of cases.2,3 Difficult intubation occurs in approximately 5% of cases, with impossible intubation (i.e., failed intubation after multiple attempts at direct laryngoscopy) occurring in 0.3% to 0.5% of cases.4 The incidence of both occurring in combination is very low, at less than 2 in 10,000 intubations.2
Failure to control an airway in a timely and reliable manner has been associated with a high degree of morbidity and mortality.5,6 Attempts to predict difficulty with airway management and mitigate its impact have met limited success. The ASA proposes 11 anatomic “predictors” of difficulty for intubation and five for mask ventilation.1 No specific group of these “predictors” has been able to reliably identify problematic airways in advance.6-8 Complex algorithmic models leave a wide “gray area” of uncertainty.9 Most difficult airways appear to be unanticipated, even with use of these models.7 This leaves the Emergency Physician with a critically important dilemma while under a significant time constraint.
The focus has slowly shifted away from prediction and toward standardized algorithmic approaches. The ASA difficult airway algorithm and the Difficult Airway Society (DAS) algorithms were groundbreaking developments. They were criticized for containing multiple decision points that added complexity without improving outcomes.10 The favored approach has been extensive training in an institutionally defined, forward-only algorithm for management of the difficult airway.10,11 This is often combined with a dedicated team of providers proficient in its use.12,13 This works for Anesthesiologists but not for Emergency Physicians working in Emergency Departments with limited backup.
No single method has been endorsed by airway societies. The above approach remains promising due to several key advantages. It offers clear steps in a timely progression to minimize harm and maximize success.14,15 An “open-box” approach allows for substitution of locally available tools and techniques within the chain of progression.13 Standardized simulation training using such algorithms has demonstrated improved compliance and patient outcomes.15-17 Availability of the necessary tools and proficiency in their use are the keys to maximizing success in managing the difficult airway.18,19 However, the tools and proficiency are often lacking in many instances.18,19
ANATOMY OF THE DIFFICULT AIRWAY
A full overview of airway anatomy and its evaluation is contained in the ...