• G Plourde, D Joffe, C Villemure, and M Trahan.
• Department of Anaesthesia, McGill University, Montreal, Quebec, Canada.
• Anesthesiology. 1993 Mar 1; 78 (3): 498-509.

BackgroundThe N1 and P3 waves of the auditory event-related potential provide information on consciousness and cortical function. The N1 wave is reduced during states of low vigilance. The P3 wave occurs only for stimuli that somehow capture the subject's attention. There are two types of P3:P3a and P3b. The P3a predominates frontally and probably occurs when the subject simply notices the stimulus. The P3b predominates parietally and indicates conscious awareness of the evoking stimulus. The N1 and P3 were recorded in 12 patients during cardiac surgery under sufentanil anesthesia to search for unintentional awareness. The study was limited to the period before cardiopulmonary bypass.MethodsAfter premedication with diazepam, morphine, and scopolamine, sufentanil was used for induction (mean dose, 7.9 micrograms/kg) and maintenance (4 micrograms/kg) of anesthesia. No other anesthetics were administered. Recordings were obtained before induction, during induction after loss of consciousness, after tracheal intubation before incision, and before cardiopulmonary bypass.ResultsThe N1 was attenuated significantly by sufentanil but was not abolished. The P3b occurred only during preinduction. There was no P3 during induction. There was a P3a during postintubation and precardiopulmonary bypass.ConclusionsThe attenuation of N1 from induction onward reflects a decrease in the level of arousal caused by sufentanil. A P3a during postintubation and precardiopulmonary bypass indicates that pitch discrimination at the cortical level occurs but does not prove that conscious awareness has occurred. Whether or not the P3a reflects the regaining of consciousness is not known.

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