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TECHNOLOGY, COMPUTING, AND SIMULATION

Spectral Entropy and Bispectral Index as Measures of the Electroencephalographic Effects of Propofol

Richard Klaus Ellerkmann, MD^*, Martin Soehle, MD^*, Thorsten Michael Alves^*, Vidal-Markus Liermann^*, Ingobert Wenningmann, MD^*, Heiko Roepcke, MD^*, Sascha Kreuer, MD, Andreas Hoeft, MD, PhD^*, and Jörgen Bruhn, MD^*

*Department of Anesthesiology and Intensive Care Medicine, University of Bonn; and Department of Anesthesiology and Intensive Care Medicine, University of Saarland, Homburg/Saar, Germany

Address correspondence and reprint requests to Richard Klaus Ellerkmann, MD, Sigmund Freud St. 25, 53105 Bonn, Germany. Address e-mail to richard.ellerkmann{at}ukb.uni-bonn.de.

Recently, Datex-Ohmeda introduced the Entropy Module^TM for measuring depth of anesthesia. Based on the Shannon entropy of the electroencephalogram, state entropy (SE) and response entropy (RE) are computed. We investigated the dose-response relationship of SE and RE during propofol anesthesia in comparison with the Bispectral Index^TM (BIS). Twenty patients were studied without surgical stimulus. Anesthesia was induced by a constant propofol infusion of 2000 mg/h (451 ± 77 µg·min^–1·kg^–1) via a large forearm vein. Propofol was infused until substantial burst suppression occurred (more than 50%) or mean arterial blood pressure decreased to <60 mm Hg. Hereafter, infusions were stopped until recovery of BIS values up to 60 was reached. Subsequently, the constant propofol infusion of 2000 mg/h was restarted to increase depth of anesthesia and again decreased (infusion was stopped) within the BIS value range of 40–60. The coefficient of determination (R²) and the prediction probability (P_K) were calculated to evaluate the performance of SE, RE, and BIS to predict changing propofol effect-site concentrations. R² values for SE, RE, and BIS of 0.88 ± 0.08, 0.89 ± 0.07, and 0.92 ± 0.06, respectively, were similar. The calculated P_K values, however, revealed a significant difference between SE and RE compared with BIS, with P_K = 0.77 ± 0.09, 0.76 ± 0.10, and 0.84 ± 0.06, respectively. BIS seems to show slight advantages in predicting propofol effect-site concentrations compared with SE and RE, as measured by P_K but not as measured by R².

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