Spectral Entropy And Bispectral Index As Measures Of The Eeg Effects Of Sevoflurane

Department of Anaesthesiology, University of Bonn, Bonn, Germany Background and Goal of Study: Recently entropy algorithms have been proposed as EEG measures of anesthetic drug effect [1]. Datex-Ohmeda introduced an entropy module, a new EEG monitor designed for measuring depth of anesthesia. Based on a time-frequency balanced spectral entropy the monitor calculates a State Entropy (SE) computed over the frequency range from 0.8 to 32 Hz reflecting the EEG-dominant part of the spectrum. In addition a Response Entropy (RE) is computed over the frequency range of 0.8 to 47 Hz, including both the EEG and EMG-dominant part of the spectrum. We investigated the dose response relationship of state entropy and response entropy during sevoflurane anaesthesia in comparison with bispectral index (BIS). Materials and Methods: 16 Patients (ASA I–II) were studied without surgical stimulus. Frontal electrodes for the BIS and Entropy monitor were positioned as recommended by the manufacturers. Anaesthesia was induced by sevoflurane inhalation with a tight fitting facemask. Data were automatically recorded every 5 sec. Sevoflurane concentrations were increased systematically until substantial burst suppression occurred and subsequently decreased and increased twice until the measurement was stopped and patients were intubated for surgery. The performance of state entropy, response entropy and bispectral index to predict the sevoflurane effect compartment concentration, obtained from the sevoflurane end tidal concentrations using a ke0 of 0,29 [2], were compared. Results and Discussions: State entropy, response entropy and bispectral index decreased continuously over the observed concentration range of sevoflurane. The performance of the entropy parameters (prediction probability [3] PK 0,83 0,06 for SE and 0,82 0,07 for RE) as indicators for sevoflurane effect site concentrations was similar to BIS (PK 0,80 0,06). Conclusion: State entropy and response entropy appear to be useful EEG measures of sevoflurane drug effect. References: 1 Bruhn J., Ropke H., Hoeft A., Anesthesiology, 2000; 92(3):715–26. 2 Rehberg B., Bouillon T., Zinserling J. et al, Anesthesiology, 1999; 91(2):397–405. 3 Smith W.D., Dutton R.C., Smith N., Anesthesiology, 1996; 84(1):38–51.