The Expected Difficult Airway

Abstract

The primary purpose of airway management is to oxygenate the patient, as loss of airway is associated with hypoxemia causing significant morbidity and mortality. Patients need successful airway management as part of a general anesthetic or for resuscitation when a patient is in extremis. Difficulty with achieving satisfactory ventilation and oxygenation is a medical emergency, where prevention is better than the cure, and adverse outcomes follow rapidly with unprepared attempts by unskilled practitioners. Ever since the ASA closed claims studies [1], the critical importance of recognizing the difficult airway and preventing hypoxia has been a primary aspect of airway training. The advent of neuromuscular relaxants in the 1950s ushered in an era of tracheal intubation as this was considered the most effective way to ensure adequate ventilation during surgery. As a result, the vast majority of published literature looks at prediction of difficult tracheal intubation. However, mask ventilation is an equally critical component of successful airway management. Successful mask ventilation provides practitioners with a rescue technique during unsuccessful attempts at laryngoscopy and unanticipated difficult airway situations. Difficulty with both tracheal intubation and mask ventilation is associated with increased risk of patient injury. Several clinical models and tests have been described for the prediction of difficult intubation and mask ventilation. These screening tests use history elements and quantitative or estimated measures of various aspects of the face, upper airway, and neck to ascribe either high or low risk of an expected difficult airway. In order to better understand the performance and accuracy of these tests, a working understanding of the anatomy of the structures of interest is essential. A variety of systemic and local tissue factors impact the ease of tracheal intubation and mask ventilation. While the elective situation permits a rigorous examination of the airway, certain urgent and emergent clinical scenarios preclude a complete and thorough airway examination, making difficult airway situations more likely but less predictable. Irrespective of the urgency of airway instrumentation, clinical suspicion of a difficult airway helps prepare the practitioner for backup airway management strategies that often require additional personnel, equipment, and techniques for successful tracheal intubation. The purpose of this chapter is to describe the clinical features associated with the difficult airway and explore the clinical utility of these features on prediction of difficult mask ventilation and difficult tracheal intubation.