AUDITORY STEADY-STATE RESPONSE, UPPER FACIAL EMG, EEG AND HEART-RATE AS PREDICTORS OF MOVEMENT DURING ISOFLURANE NITROUS-OXIDE ANESTHESIA

We have studied the relationship between patient movement and changes in the auditory steady-state evoked potential, upper facial muscle ele ctromyogram (FEMG), electroencephalographic-zero crossing frequency (E EG-ZCF) and heart rate during emergence from anaesthesia. Twelve healt hy patients underwent surgery during stable isoflurane-nitrous oxide-o xygen anaesthesia without neuromuscular block. After skin closure, ana esthesia was discontinued abruptly while mechanical ventilation was co ntinued until the patient moved. The magnitude of change in each physi ological signal was evaluated in decibels (dB). Both the auditory stea dy state evoked potential and FEMG showed significant increases in amp litude during the last 5-min period before movement (6.1 and 10.7 dB, respectively). EEG-ZCF increased rapidly after anaesthesia was discont inued (2.5 dB) but there was no further increase in activity before mo vement. Heart rate did not change before movement. The use of the deci bel transformation offers a promising method of displaying and interpr eting changes in physiological variables during anaesthesia.