• D Hadzidiakos, S Petersen, J Baars, K Herold, and B Rehberg.
• Charité, Universitaetsmedizin Berlin, Campus Virchow-Klinikum and Campus Charité Mitte, Department of Anaesthesiology and Intensive Care Medicine, Berlin, Germany. daniel.hadzidiakos@charite.de
• Eur J Anaesthesiol. 2006 Nov 1;23(11):931-6.

Background And ObjectiveDerived parameters of the electroencephalogram and auditory evoked potentials can be used to determine depth of anaesthesia and sedation. However, it is not known whether any parameter can identify the occurrence of awareness in individual patients. We have compared the performance of bispectral index and a new composite index derived from auditory evoked potentials and the electroencephalogram (AAI 1.61) in predicting consciousness, explicit and implicit memory during moderate sedation with propofol.MethodsTwenty-one patients with spinal anaesthesia received intraoperatively propofol at the age-corrected C(50) for loss of consciousness and were presented test words via headphones. Bispectral index and AAI 1.61 (auditory evoked potentials, AEP-Monitor2) were recorded in parallel as well as the Observer's Assessment of Alertness/Sedation-score. Postoperatively, testing for explicit and implicit memory formation was performed.ResultsBispectral index and AAI 1.61 correlated well with loss of consciousness defined by an Observer's Assessment of Alertness/Sedation-score of 2 (identical P(K) of 0.87), but did not allow a prediction of postoperative explicit or implicit recall.ConclusionsBoth bispectral index and AAI may be indices of depth of sedation rather than indicators of memory formation, which persists during propofol sedation even after loss of consciousness.

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