Closed-loop feedback controlled administration of alfentanil during alfentanil-nitrous oxide anaesthesia.

We have studied the automatic administration of alfentanil during alfentanil-nitrous oxide anaesthesia in 11 patients using a closed-loop feedback control system based on EEG analysis. We chose a median EEG frequency of 2-4 Hz as the EEG set point. The slope of the asymptote to the cumulative dose requirement was used to define an effective therapeutic infusion of alfentanil. Median EEG frequency (mean (SD)) during the feedback period was 3.03 (0.45) Hz. The average effective therapeutic infusion of alfentanil was 0.140 (0.032) mg min-1. We conclude that EEG feedback control may be useful in assessing and defining the dose requirements of alfentanil.