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<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<0.01).