VECURONIUM NEUROMUSCULAR BLOCKADE AT THE CRICOTHYROID AND POSTERIOR CRICOARYTENOID MUSCLES OF THE LARYNX AND AT THE ADDUCTOR POLLICIS MUSCLE IN HUMANS

Study Objective: To compare the sensitivity to vecuronium in the cricothyroid (CT) and posterior cricoarytenoid (PCA) muscles of the larynx and the adductor pollicis muscles. Design: Prospective, nonrandomized study. Setting: Operating room at Sapporo Medical College and Hospital. Patients: 9 ASA status I and II adult patients scheduled for total laryngectomy to resect laryngeal cancer of essentially unilateral involvement. Interventions: During surgery electromyographic (EMG) recording wire electrodes were inserted into the CT and PCA muscles with nitrous oxide, oxygen, and fentanyl anesthesia. The evoked compound EMG responses of the CT and PCA muscles were quantified simultaneously in an identical manner by supramaximally stimulating the superior laryngeal and recurrent nerves at 0.1 Hz. and 0.2 millisecond. The ulnar nerve also was stimulated, and the adduction force of the thumb was measured. Vecuronium was infused continuously at a rate of 0.01 mg/kg/min. The evoked responses (percentage of control, means +/- so) of the adductor pollicis, CT and PCA muscles were 12.0 +/- 4.2, 22.0 +/- 5.3, and 32. 9 +/- 7.8, respectively G minutes after vecuronium administration. Measurements and Main Results: Vecuronium produced significantly more intense neuromuscular blockade in the adductor pollicis than in the laryngeal muscles (p < 0.05). In comparing the laryngeal muscles, the depression of EMG at the CT was significantly greater than that at the PCA (p < 0.05). Conclusions: The laryngeal (CT and PCA) muscles are more resistant to vecuronium than is the adductor pollicis, and the PCA muscle is more resistant to vecuronium than is the CT muscle. This finding suggests that partially paralyzed patients are able to maintain laryngeal patency despite the apparent impaired neuromuscular transmission in the adductor pollicis muscle.