Background: To prevent awareness and uterine atony among parturients during general anesthesia for caesarean section, volatile anesthetic agents have been limited to 0.5 MAC in 50% N2O. This technique appeared to be inadequate to produce BIS values less than 60 in isoflurane and sevoflurane.
Objective: To assess BIS value during general anesthesia with 3% and 4.5% desflurane in 50% N2O before delivery.
Material and Method: The parturients were blinded and randomized in opaque envelopes to one of the two study groups. Seventy-two elective caesarean section ASA I - II parturients were induced and intubated with thiopental 4 mg/kg, succinylcholine 1.5 mg/kg and were received either 3% or 4.5% desflurane in 50% N2O to maintain general anesthesia. Both groups received rocuronium 0.6 mg/kg for muscle relaxation. Morphine 0.1 mg/kg and midazolam 0.06 mg/kg were administered after delivery.
Results: There were no differences in demographic data in both groups. The incidences of patients with a satisfactory BIS score (< 60) in the 4.5% desflurane group was 81% that was significantly more than 42% in the 3% desflurane group (p < 0.000). Mean BIS values at neonatal delivery were 62 + 8 in the 3% desflurane group, versus 49 + 12 in the 4.5% desflurane group. Indices of maternal and neonatal outcome were similar between the two groups.
Conclusion: General anesthesia for caesarean section with 4.5% desflurane in 50% N2O maintained BIS < 60 more significantly than 3% of desflurane in 50% N2O without maternal and neonatal adverse effects in healthy paturients.

Keywords: BIS, Bispectal index, Caesarean section, Desflurane