The influence of sevoflurane on the bispectral index, regional cerebral oxygen saturation, and propofol concentration during propofol/N2O anesthesia

Objective This study was undertaken to investigate the influence of sevoflurane on the bispectral index (BIS), regional cerebral oxygen saturation (rSO₂), and serum propofol concentration during propofol/N₂O anesthesia. This study tested the hypothesis that sevoflurane affect BIS values, rSO₂, and the pharmacokinetics of propofol during propofol/ N₂O anesthesia.Methods General anesthesia was administered to 15 ASA I-II patients with a continuous infusion of propofol to maintain a BIS value of 45 ± 5. After recording baseline values, patients were assigned to receive sevoflurane (2.0%, 20 min). BIS values, rSO₂ using near-infrared spectroscopy, and hemodynamic parameters were recorded for 60 min. Cardiac output (CO) and stroke volume (SV) were evaluated using impedance cardiograph methods. Propofol concentration was determined using high-performance liquid chromatography.Results Sevoflurane (2.0%, 20 min) decreased the BIS score from 47.4 ± 8.2 to 27.3 ± 5.9 (P < 0.01, n = 15) without affecting rSO₂. Sevoflurane decreased systolic blood pressure from 112.1 ± 14.0 mmHg to 96.5 ± 13.2 mmHg (P < 0.001, n = 15) without affecting heart rate. Both CO and SV were significantly decreased during sevoflurane application. Propofol concentration was increased from 2.71 ± 0.51 μg/ml to 3.30 ± 0.57 μg/ml (P < 0.05) after sevoflurane application, and was returned to baseline after sevoflurane washout.Conclusions We have shown that sevoflurane decreases BIS values during propofol/N₂O anesthesia without affecting rSO₂ and that this change is accompanied by an increase in serum propofol concentration. Changes in propofol concentration may be due to, at least in part, hemodynamic changes such as decreased CO produced by sevoflurane.A part of the present study was presented at the Annual Meeting of the American Society of Anesthesiologists, October 23–27, 2004 in Las Vegas, Nevada, USA.Nishikawa K, Kanemaru Y, Hagiwara R, Goto F. The influence of sevoflurane on the bispectral index, regional cerebral oxygen saturation, and propofol concentration during propofol/N₂O anesthesia.