Halothane-induced variability in the neuromuscular transmission of patients with myasthenia gravis.

The purpose of the present clinical study was to explore the skeletal muscle mechano (MMG)- and electromyographic (EMG) responses during halothane/oxygen/air anaesthesia in patients with myasthenia gravis (MG) compared with patients with normal neuromuscular transmission. The majority of MG-patients had a significant decremental response of the evoked muscle action potentials to a train-of-four (TOF) stimulation during halothane exposure (mean decrease of train-of-four ratio was 33% during the highest mean halothane concentration of 1.9 MAC). An excellent correlation was found between MMG- and EMG-measurements (r2 = 0.878, P less than 0.001). However, marked individual variations in the neuromuscular response to halothane were seen. Neither preoperative muscle fatigability nor acetylcholine receptor antibodies predicted the decremental muscle responses produced by halothane among MG-patients. The increased presence of HLA-B8 among myasthenics with halothane-suppressed muscle responses after TOF stimulation could be demonstrated (P less than 0.01).