Auditory evoked potential index predicts the depth of sedation and movement in response to skin incision during sevoflurane anesthesia

Background: The auditory evoked potential (AEP) index, which is a single nu merical parameter derived from the AEP in real time and which describes the underlying morphology of the AEP, has been studied as a monitor of anesthe tic depth. The current study was designed to evaluate the accuracy of AEPin dex for predicting depth of sedation and anesthesia during sevoflurane anes thesia. Methods. In the first phase of the study, a single end-tidal sevoflurane co ncentration ranging from 0.5 to 0.9% was assigned randomly and administered to each of 50 patients. The AEPindex and the Bispectral Index (BIS) were o btained simultaneously. Sedation was assessed using the responsiveness port ion of the observer's assessment of alertness-sedation scale. in the second phase of the study, 10 additional patients were included, and the 60 patie nts who were scheduled to have skin incisions were observed for movement in response to skin incision at the end-tidal sevoflurane concentrations betw een 1.6 and 2.6%. The relation among AEPindex, BIS, sevoflurane concentrati on, sedation score, and movement or absence of movement after skin incision was determined. Prediction probability values for AEPindex, BIS, and sevof lurane concentration to predict depth of sedation and anesthesia were also calculated. Results: The AEPindex, BIS, and sevoflurane concentration correlated closel y with the sedation score. The prediction probability values for AEPindex, BIS, and sevoflurane concentration for sedation score were 0.820, 0.805, an d 0.870,respectively, indicating a high predictive performance for depth of sedation. AEPindex and sevoflurane concentration successfully predicted mo vement after skin (prediction probability = 0.910 and 0.857, respectively), whereas BIS could not (prediction probability = 0.537). Conclusions. Auditory evoked potential index can be a guide to the depth of sedation and movement in response to skin incision during sevoflurane anes thesia.