Power spectral analysis of EEG during sufentanil infusion in humans.

The purpose of this study was to examine the relationship of continuous sufentanil infusion (0.71 micrograms.kg-1.min-1 for 14 min) and the response of the power spectrum of the electroencephalogram (EEG) performed during the induction of anaesthesia in 12 patients undergoing CABG surgery. Data were collected at various times including the preinduction period, every minute during the infusion period (minute 0 to 14), and 15, 20 and 25 min after the start of the infusion (1, 6 and 11 min respectively after completion of the infusion). Within three minutes of the sufentanil infusion, the total power and the relative power of delta increased to near maximum, while the 95% spectral edge and the mean frequency decreased markedly. In spite of the continued infusion of sufentanil, there were very little further changes in the EEG activity. This ceiling effect for the EEG changes appear to coincide with the failure to respond to verbal command. We conclude that the power spectrum of the EEG failed to respond to increasing doses of sufentanil during its infusion after the rapid initial changes.