• A Silva, D A Ferreira, C Venâncio, A P Souza, and L M Antunes.
• Veterinary Sciences Department, Universidade de Trás-os-Montes e Alto Douro, Vila Real, Portugal. aurasilva@utad.pt
• Br J Anaesth. 2011 Apr 1;106(4):540-7.

BackgroundThe index of consciousness (IoC), the permutation entropy (PE), and the approximate entropy are recent EEG-derived indices of anaesthetic depth. In this study, a rabbit model under fentanyl and isoflurane anaesthesia was used to compare the performance of these indices and also the classic median and spectral edge frequency 95%.MethodsEEG recordings were obtained from six rabbits. Animals received fentanyl for premedication, followed by induction with propofol and maintenance with isoflurane. Anaesthetic depth was evaluated according to a clinical scale from 1 (awake) to 4 (surgical anaesthesia). Animals were submitted to surgical implantation of a small device in the lumbar muscles. A correction factor for the EEG suppression ratio was applied to the spectral parameters and to the PE. The correlation of the indices with the clinical scale of anaesthesia was analysed using prediction probability. Repeated-measures analysis of variance or its non-parametric equivalent was used to analyse the indices values at the study times and to compare their variability.ResultsThe IoC showed the best mean prediction probability value [0.94 (0.01)] followed by burst suppression-corrected PE [0.91(0.03)]. Both parameters also showed less variability than the others.ConclusionsThe IoC and PE are promising indices for anaesthetic depth monitoring. The PE might benefit from the application of a burst suppression correction at deeper stages of anaesthesia. The rabbit is useful as a translational research animal model for the validation of clinical indices.

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