Using the laryngeal indices caliper to predict difficulty of laryngoscopy with a Macintosh #3 laryngoscope

Abstract

Study objective: (1) To evaluate a device of the authors' design, the laryngeal indices caliper, which quantitates the position of the anterior edges of the larynx relative to the upper teeth and the external auditory canals; (2) to determine how relative laryngeal position affects ease of direct laryngoscopy with a Macintosh #3 laryngoscope.

Design: Randomized, double-blind study.

Setting: Inpatient surgery center at a university medical center.

Patients: 101 renal lithotripter patients.

Interventions: Patients were measured with the laryngeal indices caliper prior to induction of general endotracheal anesthesia. They were then given a sleep dose of thiopental sodium (4 mg/kg) and paralyzed with a bolus dose of succinylcholine (1 mg/kg).

Measurements and main results: Of the measurements taken or calculated, only laryngeal tilt (LT) showed a significant correlation with grade of difficulty of laryngoscopy. When the anterior surface of the thyroid cartilage was tilted more than 20 degrees anteriorly to a line perpendicular to the laryngeal indices line, the vocal cords could not be seen in 83% of the patients.

Conclusions: (1) Laryngeal tilt is a good predictor of difficulty of laryngoscopy with a Macintosh #3 laryngoscope; (2) the laryngeal indices caliper is a simple pocket device to measure LT indirectly.