A study of bispectral analysis and auditory evoked potential indices during propofol-induced hypnosis in volunteers - The effect of an episode of wakefulness on explicit and implicit memory

The bispectral index (BIS) and the auditory evoked potential (A-EP) index a s calculated by the new A-line monitor were measured during hypnosis with p ropofol, which included an episode of wakefulness. Both indices followed a similar pattern during sedation, with values decreasing with sedation and i ncreasing when awake. Baseline AEP values varied between 60 and 98, and BIS values were between 96 and 98. The AEP-index value was at all times 10-20 points lower than the BIS-index. The transition to loss of response occurre d at a mean AEP value of 46 and BIS value of 58. The transition to just res ponding following a period of unconsciousness occurred at a mean AEP value of 46 and BIS 65. Both monitoring techniques, however, displayed large inte rindividual variations making it impossible to discriminate in real time be tween subtle changes of clinical state. The new neurophysiological monitors A-line AEP and BIS are interesting tools for creating a better understandi ng of the anaesthetic effects of drugs; however, further refinements are re quired before their relative roles can be fully established in the clinical setting.