[The pharmacodynamics of vecuronium on the musculature of the vocal cords and the ball of the thumb. Preliminary report].

During endolaryngeal microsurgery, an attempt was made to quantify laryngeal muscle relaxation by electromyographic recording of evoked responses from the vocal cord musculature in 5 patients. Both mechanographic and electromyographic recordings from the adductor pollicis were obtained simultaneously. Following a bolus dose of vecuronium (60 micrograms/kg, n = 3, and 100 micrograms/kg, n = 2), nearly total (97%-100%) suppression of evoked responses at the peripheral muscle site was observed; the vocal cords, however, did not show complete neuromuscular (nm) blockade, but rather varying degrees of nm depression ranging from 61%-92%. The present results clearly show that quantitative information as to duration and degree of neuromuscular depression in the vocal musculature may be obtained by electromyographic recordings of evoked potentials in the clinical setting; it is impossible however, to quantitatively estimate the extent of intrinsic laryngeal muscle relaxation from peripheral nm depression. The pharmacodynamic differences observed might be due to the varying acetylcholine receptor density of the muscle groups studied.