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


METHODS
Randomized, double-blind study.


METHODS
Inpatient surgery center at a university medical center.


METHODS
101 renal lithotripter patients.


METHODS
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).


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.
Roberts
J T
JT
Department of Anesthesia, Massachusetts General Hospital, Boston 02114.
Ali
H H
HH
Shorten
G D
GD
D004311:Double-Blind Method; D005069:Evaluation Studies as Topic; D005260:Female; D006801:Humans; D007669:Kidney Calculi / Q000628:therapy; D020704:Laryngoscopes; D007828:Laryngoscopy / Q000379:methods; D008096:Lithotripsy; D008297:Male