AUDITORY-EVOKED POTENTIAL INDEX - A QUANTITATIVE MEASURE OF CHANGES IN AUDITORY-EVOKED POTENTIALS DURING GENERAL-ANESTHESIA

We describe a novel index derived from the auditory evoked potential, the auditory evoked potential index, and we compare it with latencies and amplitudes related to clinical signs of consciousness and unconsci ousness. Eleven patients, scheduled for total hire replacement under s pinal anaesthesia, completed the study The initial mean (SD) value of the auditory evoked potential index was 72.5 (11.2). During the first period of unconsciousness it decreased to 39.6 (6.9) and returned to 6 6.8 (12.5) when patients regained consciousness. Thereafter, similar v alues were obtained whenever patients lost and regained consciousness. Latencies and amplitudes changed in a similar fashion. From all param eters studied, Na latencies had the greatest overlap between successiv e awake and asleep states. The auditory evoked potential index and Nh latencies had no overlay. The consistent changes demonstrated suggest that the auditory evoked potential index could be used as a reliable i ndicator of potential awareness during propofol anaesthesia instead of latencies and amplitudes.