• Richard Klaus Ellerkmann, Vidal-Markus Liermann, Thorsten Michael Alves, Ingobert Wenningmann, Sascha Kreuer, Wolfram Wilhelm, Heiko Roepcke, Andreas Hoeft, and Jörgen Bruhn.
• Department of Anesthesiology and Intensive Care Medicine, University of Bonn, Bonn, Germany. richard.ellerkmann@ukb.uni-bonn.de
• Anesthesiology. 2004 Dec 1;101(6):1275-82.

BackgroundRecently, entropy algorithms have been proposed as electroencephalographic measures of anesthetic drug effects. Datex-Ohmeda (Helsinki, Finland) introduced the Entropy Module, a new electroencephalographic monitor designed for measuring depth of anesthesia. The monitor calculates a state entropy (SE) computed over the frequency range of 0.8-32 Hz and a response entropy (RE) computed over the frequency range of 0.8-47 Hz. The authors investigated the dose-response relation of SE and RE during sevoflurane anesthesia in comparison with the Bispectral Index (BIS).MethodsSixteen patients were studied without surgical stimulus. Anesthesia was induced by sevoflurane inhalation with a tight-fitting facemask. Sevoflurane concentrations were increased and subsequently decreased and increased two to four times until the measurement was stopped and patients were intubated for surgery. The performances of SE, RE, and BIS to predict the estimated sevoflurane effect site concentration, obtained by simultaneous pharmacokinetic and pharmacodynamic modeling, were compared by calculating the correlation coefficients and the prediction probability.ResultsState entropy, RE, and BIS values decreased continuously over the observed concentration range of sevoflurane. Correlation coefficients were slightly but not significantly better for entropy parameters (0.87 +/- 0.09 and 0.86 +/- 0.10 for SE and RE, respectively) than for BIS (0.85 +/- 0.12). Calculating the prediction probability confirmed these results with a prediction probability of 0.84 +/- 0.05 and 0.82 +/- 0.06 for SE and RE, respectively, and 0.80 +/- 0.06 for BIS.ConclusionState entropy and RE seem to be useful electroencephalographic measures of sevoflurane drug effect.

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