Mid-latency auditory evoked potentials and wakefulness during caesarean section.

We investigated intra-operative wakefulness and mid-latency auditory evoked potentials (MLAEP) in 20 patients undergoing elective Caesarean section under general anaesthesia. Anaesthesia was induced with thiopentone 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 fentanyl 0.2-0.3 mg i.v., enflurane 0.4-1.0 vol% end-expired concentration and 50% N2O in oxygen. Purposeful movements were interpreted as signs of inadequate anaesthesia and intra-operative wakefulness. They were recorded as either spontaneous movements or in response to one of two audio tapes (tape A: sound of a crying baby; tape B: classical music). Post-operatively, intra-operative dreams, hallucinations and detailed reports about intra-operative events were evaluated. Auditory evoked potentials were recorded online before and during general anaesthesia. Twenty spontaneous purposeful movements were observed in 12 patients, seven before or during delivery and 13 after delivery. Four purposeful movements were observed after presentation of the sound of a crying baby 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 amplitudes and a periodic waveform. Under adequate levels of general anaesthesia MLAEPs showed a marked increase in latency and decrease in amplitude or were even suppressed completely. This increase in latencies and decrease in amplitude of MLAEP was absent in patients who reported intraoperative events and during spontaneous or provoked motor reactions.