Survey on the adequacy of depth of anaesthesia with bispectral index and isolated forearm technique in elective Caesarean section under general anaesthesia with sevoflurane

Abstract

Awareness during general anaesthesia for Caesarean section (C/S), although uncommon, remains a concern for anaesthesiologists. We examined the relationship between the bispectral index (BIS) and responses to the isolated forearm technique (IFT) to evaluate the adequacy of general anaesthesia in C/S and determine a suitable cut-off point for BIS values based on IFT results. In 61 parturients, a standardized anaesthetic technique was applied. It included sodium thiopental and succinylcholine for induction, and O2, N2O, and sevoflurane for maintenance of anaesthesia. BIS values and IFT response were recorded at 16 predetermined events during anaesthesia. Positive IFT responses were seen in 41%, 46%, and 23% of the parturients at laryngoscopy, intubation, and skin incision, respectively. BIS could not reliably differentiate between IFT responders and non-responders during these three stages. The receiver operating characteristic curve cut-off points for BIS to predict IFT responders with 100% sensitivity were 34, 37, and 27, respectively, for these stages. In all stages of the operation after skin incision, more than 90% of parturients had no IFT test response, and BIS values between 40 and 63 were associated with negative IFT results. During a structured interview within 12-24 h after the operation, no patient had evidence of explicit recall of intraoperative events. The BIS is not reliable for monitoring anaesthesia depth in C/S. Lower than previously recommended values are needed to avoid IFT test responses during laryngoscopy, intubation, and skin incision.