ACOUSTIC REFLECTOMETRY AND ENDOTRACHEAL INTUBATION

To determine whether acoustic reflection measurement of the upper airw ay can be used to identify tracheas that are difficult to intubate, we conducted a pilot study of adults with a documented history of unexpe cted failed endotracheal intubation (16 cases) and compared them with 16 controls with previous successful intubation. The two groups were m atched by age, sex, height, and weight. Acoustic reflection measuremen ts of airway cross-sectional area versus distance were made at six com binations of body (upright and supine) and neck (flexed, neutral, and extended) positions. Cumulative airway volumes were calculated from th e incisors to the glottis, and these were subdivided into oral and pha ryngeal volumes. For supine position with the neck extended, all patie nts who had been successfully intubated had pharyngeal volumes more th an 43.4 mL (mean +/- SD, 56.9 +/- 8.3 mL), whereas pharyngeal volumes were less than 37.5 mL in all patients who had a history of unexpected failed intubation (mean +/- SD, 19.7 +/- 10.2 mL; P < 0.05). Using a cutoff of 40.2 mL, acoustic reflection enabled us to distinguish betwe en patients with previous unexpected failed endotracheal intubation an d those with previous successful intubation.