• J T Roberts, H H Ali, and G D Shorten.
• Department of Anesthesia, Massachusetts General Hospital, Boston 02114.
• J Clin Anesth. 1993 Jul 1; 5 (4): 302-5.

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.DesignRandomized, double-blind study.SettingInpatient surgery center at a university medical center.Patients101 renal lithotripter patients.InterventionsPatients 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 ResultsOf 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.

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