Preoperative evaluation

The anesthesia provider should preoperatively interview the patient and review the medical record to determine whether the patient has had any previous difficulty while being intubated. Three classic bedside measurements should be obtained: the size of the tongue, as compared with the pharynx; the extension of the atlanto-occipital joint; and the size of the anterior mandibular space. Although none of these parameters is a definitive predictor of airway ease or difficulty, evaluation of as many bedside measures as possible is recommended to increase the predictive power of the preoperative examination. In addition to obtaining the three classic measures, incisor prominence, interincisor distance, width of the palate, temporomandibular joint mobility, and length and thickness of the neck should also be evaluated.

Tongue versus pharyngeal size

Preinduction visualization of the faucial pillars, soft palate, and base of the uvula, with the patient in a sitting position, is used to classify patients according to how well pharyngeal structures can be seen (Table 240-1 and Figure 240-1). Mallampati and colleagues’ original recommendation was to examine these structures without the patient phonating and to assign a class level—I through III (see Table 240-1)—to the results. Class II was later subdivided based on whether all of the uvula or only its base can be visualized.

Table 240-1

Mallampati Classification of the Upper Airway

Class	Visible Structures
I	Palate, faucial pillars, entire uvula
II	Palate, faucial pillars, base of uvula
III	Palate, some of the faucial pillars
IV	Palate

Defining the difficult airway

By definition, a difficult airway is a clinical situation in which an anesthesia provider experiences difficulty with facemask ventilation of the upper airway, with direct laryngoscopy, or with tracheal intubation. In the 1990s, the American Society of Anesthesiologists (ASA) developed the first practice guidelines and an algorithm for managing the difficult airway and began emphasizing that anesthesia providers needed to learn multiple airway management techniques. This instruction led to anesthesia providers’ increased familiarity with multiple airway instruments and a willingness to switch techniques sooner, rather than later, when encountering a difficult airway. The 2013 update of the ASA Difficult Airway Algorithm (Figure 240-2) mentions the use of video laryngoscopy as another useful approach. This mirrors the widespread adoption of video laryngoscopy techniques by most anesthesia providers as their favored approach to anticipated difficult airways.

Management of the difficult airway

The anesthesia provider may have more difficulty mask ventilating a morbidly obese patient (i.e., body mass index > 40 kg/m²), but morbid obesity does not, per se, lead to difficulty in intubating the airway unless the patient has increased periglottic tissue or limited neck mobility or if problems are encountered in positioning the patient. Additionally, obese patients develop rapid O₂ desaturation during apnea. These factors can be ameliorated by placing the patient in a “ramped up” position (see Chapter 163).

Only rarely is a surgical airway the first choice for securing an airway. The most common reasons include trauma to the face or cervical spine or a neoplastic disease involving the airway or neck. Because of the differences in managing the airway of patients with trauma, the ASA modified the Difficult Airway Algorithm for use in trauma patients (Figure 240-3).

Identification of a difficult airway after the induction of general anesthesia and administration of neuromuscular blocking drugs leads to the arm of the algorithm that is most stressful for the anesthesia provider. In this circumstance, rapid decisions must be made, and both equipment and knowledge must be immediately available. The anesthesia provider must always be prepared to manage the airway with transoral supraglottic techniques (e.g., laryngeal mask airway, Combitube) as well as with techniques involving emergency invasive airway access (surgical or percutaneous cricothyrotomy plus transtracheal jet ventilation) while moving toward achieving a more definitive airway. Patient safety depends on planning ahead and progressing rapidly down the appropriate arms of the algorithm. Studying the algorithm and being aware of the potential pathways before encountering airway difficulties is likely to result in the best outcome.