Does Bispectral Index Monitoring Detect the Sedative Effect of Epidural Anesthesia?

Background: Epidural anesthesia has been shown to a have direct sedative effect and to markedly reduce the amount of hypnotic agents required for sedation.A Bispectral Index (BIS) is a useful monitor of the level of sedation and loss of consciousness for several anesthetics including propofol.In this study, we investigated whether BIS monitoring could detect the sedative effect of epidural anesthesia during propofol induction.Methods: Twenty patients scheduled for elective lower abdominal surgery were included.A Target controlled infusion (target effect concentration 5μg/ml, induction time 3 min) of propofol was administered to the patients with or without epidural anesthesia (2% lidocaine 15 ml) at the L2-3 level.The OAA/S scale and BIS were evaluated 20 min after epidural injection.Hypnotic requirements of propofol were determined using loss of eye opening in response to verbal command as an endpoint.At the time of induction of hypnosis, the target concentration, target effect concentration and BIS were recorded.Results: Epidural lidocaine significantly decreased the hypnotic dose of propofol (1.0 ± 0.2μg/ml vs. 1.3 ± 0.1μg/ml; P = 0.0008), hypnotic calculated concentration (3.3 ± 0.6μg/ml vs. 4.1 ± 0.3 μg/ml; P = 0.0007), and the hypnotic effect concentration (0.7 ± 0.3μg/ml vs. 1.1 ± 0.1μg/ml; P = 0.0007).In the patients with epidural anesthesia, the OAA/S scale was decreased without a change of the BIS after epidural anesthesia and BIS recorded at the time of induction of hypnosis was much higher in patients with epidural anesthesia than in patients without epidural anesthesia (92.7 ± 2.2 vs. 85.5 ± 6.2; P = 0.0029)Conclusions: Epidural anesthesia induced a sedative effect without a change of the BIS and then induced the hypnosis with lesser dose of propofol.At the time of hypnosis, a higher BIS was noticed with epidural anestheia.These results concluded that BIS monitoring could not detect the sedative effect induced with epidural anesthesia.(Korean J Anesthesiol 2002