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Bispectral index and regional cerebral oxygen saturation during propofol/N₂O anesthesia

[L’index bispectral et la saturation en oxygène du sang cérébral régional pendant l’anesthésie au propofol/N₂O]

From the Department of Anesthesiology, Gunma University Graduate School of Medicine, Maebashi City, Japan.

Address correspondence to: Dr. Koichi Nishikawa, Department of Anesthesiology, Gunma University Graduate School of Medicine, 3-39-22 Showa-machi, Maebashi City 371-8511, Japan. Phone: +81-27-220-8454; Fax: +81-27-220-8473; E-mail: nishikaw{at}med.gunma-u.ac.jp

Purpose: A study was undertaken to compare the influence of midazolam, isoflurane, and aminophylline (which may antagonize anesthetic action) on bispectral index (BIS) and regional cerebral oxygen saturation (rSO₂) during propofol/N₂O anesthesia, and to test the hypothesis that the drug-induced changes in BIS values are accompanied by a change in rSO₂.

Methods: General anesthesia was administered to 36 patients with a continuous infusion of propofol to maintain a BIS value of 40 ± 5. After baseline recordings, patients were randomly assigned to receive either midazolam, isoflurane, or aminophylline. Bispectral index values, rSO₂ using near-infrared spectroscopy, and hemodynamic parameters were recorded for 60 min.

Results: Midazolam (0.05 mg·kg^–1) significantly decreased the BIS from 47.8 ± 5.4 to 35.0 ± 4.5 at five minutes after injection (P < 0.001 vs control) during propofol anesthesia, whereas the rSO₂ was unchanged. Similarly, isoflurane (1.1% end-tidal) decreased the BIS from 42.5 ± 7.5 to 27.8 ± 6.9 (P < 0.001) without affecting rSO₂. In contrast, aminophylline (3 mg·kg^–1) was associated with an increase in BIS from 41.6 ± 2.1 to 48.3 ± 9.2 at five minutes after injection (P < 0.05) without affecting rSO₂.

Conclusions: Midazolam or isoflurane-induced decreases in the BIS during propofol anesthesia were not accompanied by a decrease in rSO₂. Aminophylline significantly increased the BIS score during propofol anesthesia, suggesting that aminophylline can antagonize, at least in part, the sedative actions of propofol.