Effect of Pre-Exposure to Sevoflurane on the Bispectral Index in Women Undergoing Caesarean Delivery Under General Anaesthesia

Editor’s key points † This study assessed the effects of pre-exposure to sevoflurane on the bispectral index (BIS) during induction of anaesthesia for Caesarean section. † Pre-exposure to subanaesthetic concentrations of sevoflurane reduced BIS values in the period before neonatal delivery, and maintained the BIS below 60 in the interval before delivery. † Neither maternal nor Background. Patients undergoing Caesarean delivery under inhalation anaesthesia are at a high risk of awareness, especially in the period before delivery. We assessed the effects of pre-exposure to sevoflurane on the bispectral index (BIS) in the interval before delivery. Methods. Sixty-four patients undergoing elective Caesarean delivery were randomly assigned to receive 1.0‐1.1 vol% (control 1) or 1.2‐1.3 vol% (control 2) end-tidal sevoflurane, or the same concentrations of end-tidal sevoflurane combined with preexposure to 1 vol% sevoflurane for the last 1 min of the preoxygenation period (the preSevo 1 and preSevo 2 groups, respectively). We assessed BIS values, arterial pressure, and heart rate at the time of induction; before intubation; and upon skin incision, uterine incision, and delivery. We also determined the maternal incidence of intraoperative awareness and the neonatal Apgar scores, and conducted umbilical blood gas analysis. Results. At skin incision, BIS values were significantly lower in the preSevo 1 group than in the control 1 group [50 (13) vs 72 (8), P,0.001] and in the preSevo 2 group than in the control 2 group [44 (11) vs 67 (10), P,0.001]. The mean BIS values in the preSevo 1 and 2 groups were maintained below 60 in the period before delivery. No other parameter differed among groups, and no patient exhibited intraoperative awareness.