Effect of epidural bupivacaine on the relationship between the bispectral index and end-expiratory concentrations of desflurane

We compared the relationship between the bispectral index and end-tidal des flurane concentrations in 20 patients undergoing elective surgery. Patients received epidurally either 10 ml saline (group S) or 10 ml bupivacaine 0.1 25% with epinephrine 1/800 000 (group B) before induction of anaesthesia wi th sufentanil (0.15 mu g.kg(-1)) and propofol (2 mg.kg(-1)); muscle relaxat ion was obtained with cisatracurium (0.2 mg.kg(-1)). Patients lungs were ve ntilated to maintain end-tidal desflurane at 3% in O-2/N2O (50/50) until 5 min after skin incision, followed by two consecutive 10 min periods at end- tidal desflurane 6% and 9% bispectral index values were recorded before ind uction, at 3% desflurane before and 5 min after skin incision, and at 6% an d 9% end-tidal desflurane. Bispectral index decreased with increasing end-t idal desflurane concentration (ANOVA: p < 0.05). The decrease in bispectral index was significant between pre-induction, 3% and 6% desflurane. No sign ificant difference was observed at 3% desflurane before and after skin inci sion, or between 6 and 9% desflurane. The relationship between bispectral i ndex and end-tidal desflurane concentration was fitted by a linear regressi on in each group. No significant difference in bispectral index was observe d between the groups at any time. We conclude that bispectral index decreas es with increasing desflurane concentration and that this relationship is n ot affected by epidural 0.125% bupivacaine.