The difficult airway is a definition that has, in the past, been retrospectively applied to an intubation that required three or more attempts or more than 10 minutes to complete (see Chapter 1, Why Airway Management Matters). There are inherent problems with such a definition that limit its utility. However, there is so much focus on the airway difficulty that the concept of “the difficult airway” remains a central part of airway management. In fact, the first key action in this book is to assess for potential difficulty or danger, and the second is to prepare for it. What does that mean, anyway? Should we abandon the term altogether or push for a greater understanding and dissemination of the potential difficulty with a patient to better inform an airway management strategy. The difficult airway is a representation of myriad factors that either individually, or in combination, make one or more aspects of airway management procedurally difficult for the clinician or physiologically dangerous for the patient.

An anatomically difficult airway is one in which identifiable anatomic attributes predict technical difficulty with glottic visualization and tracheal tube placement-in other words, difficulty for the clinician. The difficult airway exists on a spectrum and is one in which a preintubation examination identifies physical attributes that are likely to make laryngoscopy, intubation, bag-mask ventilation (BMV), the use of an extraglottic device (EGD), or surgical airway management more difficult than would be the case in a patient without those attributes. Some patients may have a single anatomic reason for airway difficulty, whereas others may have numerous difficult airway characteristics. The physiologically difficult airway is one in which underlying pathophysiology increases the risk of cardiopulmonary decompensation with airway management—in other words, dangerous for the patient.

Identifying potential difficulty is a key component of the approach to airway management for any patient to inform what approaches are, or are not, likely to be successful for that patient’s given profile of difficulty. The key reason for this is that, depending on the degree of predicted difficulty, induction of anesthesia and use of neuromuscular blocking medications would be avoided unless mask ventilation or rescue oxygenation is predicted to be successful, or compromised physiology can be optimized.

The presence of anatomic difficulty leads to a significantly increased risk of serious adverse events such as profound desaturation, aspiration, and cardiac arrest. In critically ill patients, difficult intubations are common, occurring in 10% to 20% of intubations, although lower when video laryngoscopy is used. However, studies in both the emergency department (ED) and intensive care unit (ICU) routinely show that the major risk in critically ill patients is on the second attempt, making first attempt success, rather than avoiding difficulty, the priority.^1,2,3,4 Severe cardiopulmonary complications are far less common in absence of difficulty, however, they still occur at an alarming rate. Roughly 1-in-3 to 1-in-5 intubations has a serious complication despite first attempt success, a function of the physiologically difficult airway.^5,6 Morbidity and mortality from a difficult airway occur when it degenerates into a failed airway, thus the principles of navigating through your strategy, recognizing and managing failure, and intubating with a team are paramount. There are three distinct phenotypes that contribute to the danger of an intubation when any of them encounter difficulty—underscoring the importance of diligent assessment and preparation for each. Anatomic difficulty, physiologic difficulty, and situational difficulty (i.e., human factors or airway stewardship). Each require assessment and are discussed separately in this book (Fig. 4.1).