MIDLATENCY AUDITORY-EVOKED POTENTIALS AND WAKEFULNESS DURING CESAREAN-SECTION

We investigated intra-operative wakefulness and mid-latency auditory e voked potentials (MLAEP) in 20 patients undergoing elective Caesarean section under general anaesthesia. Anaesthesia was induced with thiope ntone 5 mg kg(-1) i.v. and succinylcholine 1-1.5 mg kg(-1) i.v. After delivery, a balanced anaesthetic technique was maintained using fentan yl 0.2-0.3 mg i.v., enflurane 0.4-1.0 vol% end-expired concentration a nd 50% N2O in oxygen. Purposeful movements were interpreted as signs o f inadequate anaesthesia and intra-operative wakefulness. They were re corded as either spontaneous movements or in response to one of two au dio tapes (tape A: sound of a crying baby; tape B: classical music). P ost-operatively, intra-operative dreams, hallucinations and detailed r eports about intra-operative events were evaluated. Auditory evoked po tentials were recorded online before and during general anaesthesia. T wenty spontaneous purposeful movements were observed in 12 patients, s even before or during delivery and 13 after delivery. Four purposeful movements were observed after presentation of the sound of a crying ba by but only one after classical music. Dreams and hallucinations were reported by nine patients. Two patients reported experiencing surgical manipulations. In the awake state MLAEPs had great peak-to-peak ampli tudes and a periodic waveform. Under adequate levels of general anaest hesia MLAEPs showed a marked increase in latency and decrease in ampli tude or were even suppressed completely. This increase in latencies an d decrease in amplitude of MLAEP was absent in patients who reported i ntraoperative events and during spontaneous or provoked motor reaction s.