The performance of electroencephalogram bispectral index and auditory evoked potential index to predict loss of consciousness during propofol infusion

The bispectral index (BIS) of the electroencephalogram and middle latency a uditory evoked potentials are likely candidates to measure the level of unc onsciousness and, thus, may improve the early recovery profile. We prospect ively investigated the predictive performance of both measures to distingui sh between the conscious and unconscious state. Twelve patients undergoing lower limb orthopedic surgery during regional anesthesia additionally recei ved propofol by target-controlled infusion for sedation. The electroencepha logram BIS and the auditory evoked potential index (AEPi), a mathematical d erivative of the morphology of the auditory evoked potential waveform, were recorded simultaneously in all patients during repeated transitions from c onsciousness to unconsciousness. Logistic regression procedures, receiver o perating characteristic analysis, and sensitivity and specificity were used to compare predictive ability of both indices. In the logistic regression models, both the BIS and AEPi were significant predictors of unconsciousnes s (P < 0.0001). The area under the receiver operating characteristic curve for discrete descending index threshold values was apparently, but not sign ificantly (P > 0.05), larger for the AEPi (0.968) than for the BIS (0.922), indicating a trend of better discriminatory performance. We conclude that both the BIS and AEPi are reliable means for monitoring the level of uncons ciousness during propofol infusion. However, AEPi proved to offer more disc riminatory power in the individual patient. Implications: Both the bispectr al index of the electroencephalogram and the auditory evoked potentials ind ex are good predictors of the level of sedation and unconsciousness during propofol infusion. However, the auditory evoked potentials index offers bet ter discriminatory power in describing the transition from the conscious to the unconscious state in the individual patient.