Abstract
In order to assess 1) the time-dependent depression of neuromuscular transmission in constant depth of enflurane anesthesia and 2) the effects of differences in clinical and immunological characteristics of myasthenia gravis (MG) on the pattern of neuromus-cular responses, we examined the electromyographic responses to ulnar nerve stimula-tion in eight MG patients and seven healthy control subjects. Train-of-four (TOF) stimulation with 20-s interval was continuously applied for 120 minutes while maintain-ing end-tidal enflurane concentration constant (2.5%). Enflurane exerted a much greater neuromuscular depressant effect in MG than in normal controls. Despite the fact that alveolar concentration of enflurane was held constant, both first-twitch response (T1) and TOF ratio (TR) markedly and progressively decreased in seven of the eight MG patients. This suggests that enflurane rapidly supresses not only postjun-ctional but also prejunctional function in MG patients. The other MG patient developed no TOF-fade with inhalation of enflurane. The individual variation of neuromuscular responses to inhaled anesthetics may indicate heterogeneity of MG. However, none of the parameters, including acetylcholine receptor antibodies, clinical classification of Osserman and Genkins, Ooshima's severity grade, disease duration, and preoperative prednisolone dosage, could successfully predict the neuromuscular responses induced by enflurane. The responses were also unrelated to thymic histological findings.
