Bispectral index in assessment of adequacy of general anaesthesia for lower segment caesarean section

Awareness among parturients during general anaesthesia for caesarean section, though now uncommon, remains a concern for obstetric anaesthetists. We examined the adequacy of our general anaesthetic technique for avoiding explicit awareness by determining the depth of anaesthesia using Bispectral Index (BIS) monitoring. Twenty ASA1 parturients having general anaesthesia for lower segment caesarean section were studied. The drugs and doses used for each anaesthetic were similar Intraoperative Bispectral Index, haemodynamic parameters, end-tidal isoflurane concentration and inspired nitrous oxide fraction were measured and the postoperative incidence of explicit awareness was assessed. All anaesthetists were blinded to the Bispectral Index value throughout the operation. The depth of anaesthesia at various stages of the operation was evaluated by recording the Bispectral Index. Patients were interviewed for any intraoperative recall or awareness at the end of operation. A median BIS of 70 or below was recorded on most occasions during surgery. The range was 52 to 70, with values reaching 60 and below at intubation, uterine incision and delivery. Haemodynamic stability was satisfactory and there was no case of uterine atony, fetal compromise or postpartum haemorrhage. No patient experienced intraoperative dreams, recall or awareness. Our current general anaesthetic technique appeared inadequate to reliably produce BIS values of less than 60 that are associated with a low risk of awareness. However, no patients experienced explicit awareness.