Bispectral Index in Assessment of Adequacy of General Anaesthesia for Lower Segment Caesarean Section

Abstract

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 ASA 1 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, endtidal 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.

General anesthesia using remifentanil for Cesarean delivery in a parturient with Marfan’s syndrome

“…Cesarean delivery under general anesthesia carries a high risk for awareness, which can be associated with hyperdynamic cardiovascular responses. 18 Studies have shown that use of BIS monitoring to guide general anesthesia, reduces awareness and recovery times. 19 remifentanil has been shown to blunt increases in BIS after tracheal intubation.…”

A BIS‐guided study of sevoflurane requirements for adequate depth of anaesthesia in Caesarean section

“…They reported a reduction in the incidence of maternal awareness from 1.3 to 0.4% following the substitution of 1% isoflurane for 0.5% halothane in their practice. Yeo & Lo [1] provided additional evidence for inadequate depth as a cause of maternal awareness when they showed that isoflurane at an endtidal concentration of 0.5-0.6% did not reliably produce BIS values < 60 in Caesarean section. We subsequently confirmed this to be true also for sevoflurane at the MAC-equivalent endtidal concentration of 1% [2].…”

Awareness and recall during general anesthesia

“…The incidence of awareness related to obstetric anesthesia ranges from 0.4-1.3% [29,35,36]. Factors associated with obstetric anesthesia are rapid sequence induction and a reduced inhaled fraction of inhalant anesthetics [37]. Other risk factors for anesthesia awareness include the use of intravenous anesthesia as opposed to inhalant anesthetics and the premature lightening of anesthesia at the end of surgery to facilitate surgical turnover.…”