• Maurício Cagy and Antonio Fernando Catelli Infantosi.
• Biomedical Engineering Program, Federal University of Rio de Janeiro, Brazil.
• J Clin Monit Comput. 2002 Aug 1; 17 (6): 361-6.

ObjectiveThe mid-latency auditory evoked potential (MLAEP) has been used to indicate depth of anaesthesia, and is usually analysed in time-domain. This work compares three techniques: Wave Deformation Parameters (PDO), Auditory Evoked Potential Index (AEPidx) and an automatic Nb-wave latency estimator (Nb), in the assessment of unconsciousness onset based on EEG under auditory stimulation.MethodsTen normal adult volunteers, under no pre-anaesthetic drug administration, received propofol during two successive periods of 45 min each one (3 mg/Kg/h and 9 mg/Kg/h), being the EEG collected from 10 min previous to infusion beginning until the subjects woke up. From the time-evolution of MLAEP (averaging of successive sets of 1000 epochs) all the parameters were compared to thresholds (unconsciousness onset indication time) and the results were compared to the instant of pressing interruption of a soft-touch switch, when one assumed the volunteer became unconscious.ResultsThe Wilcoxon Signed-Rank test points equivalence between each of the parameters and the switch for, say, alpha = 5%. Bland-Altman diagrams revealed that the Attenuation-PDO has better agreement to the switch than Nb and AEPidx.ConclusionThe results suggest that, at least to indicate unconsciousness, the most reliable effect of the anaesthetic drug on MLAEP would be the amplitude attenuation. Despite the high dependence on noise due to its time-domain basis, the Attenuation-PDO seems to be adequate to assess depth of anaesthesia.

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