Remifentanil Dose/Electroencephalogram Bispectral Response During Combined Propofol/Regional Anesthesia

UNLABELLED: The effect of opioid administration on the bispectral index (BIS) during general anesthesia is controversial. Several investigators have reported BIS to be insensitive to opioid addition, whereas others have found a hypnotic response. We designed this study to examine the effect of remifentanil on BIS during combined regional/general propofol anesthesia under steady-state conditions. After Human Investigations Committee approval, 19 healthy ASA physical status I or II patients were enrolled in a prospective experimental design. Regional anesthesia was initiated and general anesthesia induced by using computer-assisted continuous infusion of propofol. Propofol was incrementally adjusted to a BIS of approximately 60. After 20 min at a stable propofol infusion rate, a remifentanil computer-assisted continuous infusion (effect-site target concentration of 0.5, 2.5, and then 10 ng/mL) was sequentially administered at stepped 15-min intervals. BIS decreased from 56 +/- 2 to 44 +/- 1, 95% spectral edge frequency from 17.9 +/- 0.5 Hz to 15.0 +/- 0.4 Hz, heart rate from 84 +/- 5 bpm to 62 +/- 4 bpm, and mean arterial blood pressure from 93 +/- 4 mm Hg to 69 +/- 3 mm Hg with increasing remifentanil concentration. A significant linear correlation between BIS, 95% spectral edge frequency, heart rate, and log (remifentanil effect-site) concentration was found. The change in baseline BIS was relatively modest but significant, suggesting that remifentanil has some sedative/hypnotic properties, or that it potentiates the hypnotic effect of propofol. IMPLICATIONS: This experiment identified a significant, dose-dependent decrease in bispectral index (BIS), 95% spectral edge frequency, heart rate, and mean arterial blood pressure with increasing remifentanil dose. The change in baseline BIS was relatively modest but significant, suggesting that remifentanil has some sedative/hypnotic properties, or that it potentiates the hypnotic effect of propofol.