Airway risk factors for the Miller laryngoscope blade.

Study Objective: The purpose of this study was to analyze previously reported airway risk factors in the performance of Miller laryngoscopy and orotracheal intubation.

Design: Prospective, observational study.

Setting: Operating rooms.

Patients: A total of 978 American Society of Anesthesiologists I-III adults requiring general orotracheal anesthesia for elective surgery.

Interventions: None.

Measurements: Nine previously reported airway risk factors used in predicting difficult laryngoscopy, modified McCormack-Lehane views observed during initial unaided Miller blade laryngoscopy, and number of attempts or need for alternate airway tools to facilitate orotracheal intubation.

Main Results: Orotracheal intubation occurred in 941 of 978 (96.2%) patients with the Miller blade, although 8 patients required 3 attempts, with the remaining 37 patients requiring alternate airway tools. There were no failed orotracheal intubations. Multivariable analysis revealed that modified Mallampati class, thyromental distance, and ability to prognath were associated with progressively inferior modified Cormack-Lehane views, whereas modified Mallampati class, height, and head and neck extension were associated with progressive difficulty with orotracheal intubation.

Conclusions: The Miller blade is highly successful in the performance of direct laryngoscopy for orotracheal intubation. These findings suggest that different sets of airway risk factors affect the process of laryngoscopy and orotracheal intubation.