USING THE LARYNGEAL INDEXES CALIPER TO PREDICT DIFFICULTY OF LARYNGOSCOPY WITH A MACINTOSH-NUMBER-3 LARYNGOSCOPE

Study Objective: (1) To evaluate a device of the authors' design, the laryngeal indices caliper, which quantitates the position of the anter ior edges of the larynx relative to the upper teeth and the external a uditory canals; (2) to determine how relative laryngeal position affec ts ease of direct laryngoscopy with a Macintosh #3 laryngoscope. Desig n: Randomized, double-blind study. Setting: Inpatient surgery center a t a university medical center. Patients: 101 renal patients. Intervent ions: 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. Wh en 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. Concl usions: (1) Laryngeal tilt is a good predictor of difficulty of laryng oscopy with a Macintosh #3 laryngoscope; (2) the laryngeal indices cal iper is a simple pocket device to measure LT indirectly.