Chapter 10. Evaluation of the Patient with a Difficult Airway

1. A patient with a history of difficult intubation should be treated as having a difficult airway, even though physical appearance and physical examination may be unremarkable.

2. A patient with anatomic variations indicative of possible difficult intubation should receive a careful history and physical examination to define the extent of the potential airway problem.

3. Possible or potentially difficult intubation may be predicted by the Mallampati test, evidence of receding mandible, limited mouth opening as a result of tissue or temporomandibular joint (TMJ) restriction, enlarged teeth, high arched palate, narrow small mouth, or restricted cervical spine movement.

4. All current tests to predict difficulty with airway management are associated with a high incidence of false-positive and false-negative results and have low predictive value. To minimize airway-related complications, it is optimal to accept a high incidence of false-positive predictions by the various tests and treat any patient identified as having a possible difficult intubation accordingly.

5. Unexpected failed ventilation and intubation may result from oropharyngeal, laryngeal, or tracheal pathology that may not be identified by external examination.

6. In pediatrics, infection-related airway compromise and congenital airway malformations are the major airway management problems.

7. In adults, stridor at rest indicates a serious degree of obstruction with a cross-sectional opening less than 4 mm.

8. Upper airway endoscopy with a standard or videolaryngoscope and/or fiberoptic bronchoscope is useful in defining anatomic challenges in patients with upper airway pathology before induction of general anesthesia.

A challenging airway may present as difficulty with ventilation, difficulty with rigid laryngoscopic tracheal intubation, or both. The American Society of Anesthesiologists' (ASA) Practice Guidelines for Management of the Difficult Airway has defined difficult ventilation as a circumstance where "it is not possible for the unassisted anesthesiologist to prevent or reverse signs of inadequate ventilation during positive pressure ventilation."1

Difficult rigid laryngoscopy is defined as a situation in which "it is not possible to visualize any portion of the vocal cords with conventional laryngoscopy." A difficult intubation is defined as a circumstance in which "the proper insertion of an endotracheal tube using conventional laryngoscopy requires more than three attempts, or greater than 10 minutes."1

The incidence of difficult intubation by rigid laryngoscopy varies from 0.5% to 13.6% in published studies.2-8 Discrepancies in the reported incidence of difficult intubation are to be expected because most reports are retrospective studies and apply different definitions of what constitutes a difficult intubation.9 The incidence of failed intubation in the general surgical population has been reported as 1 in every 2230 patients.4 The incidence of failed intubation in the parturient population has been reported as 1 in 283 to 750 patients.4,8 This represents a 3- to 10-fold increase compared with the incidence in nonparturient patients. The precise frequency of difficult mask ventilation is unknown, but an Australian study indicated that 15% of difficult intubations were also associated with difficult mask ventilation.10 In an evaluation of 22,600 attempts at mask ventilation at ...