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October 16, 2006
2:00 PM - 4:00 PM
Room Hall E, Area I
Spectral Entropy May Separate Consciousness from Unconsciousness with Both Sevoflurane and Propofol
Stefanie Pilge, M.D., Gerhard Schneider, M.D., Matthias Kreuzer, M.Sc., Eberhard F. Kochs, M.D.
Department of Anesthesiology, Klinikum Rechts der Isar, TU München, Munich, Germany
Introduction: The Entropy Module is one of the newer devices which claim to measure the hypnotic component of anesthesia. On the basis of frontal EEG and EMG signals, two spectral-entropy-based indices are calculated: response entropy, RE (0.8-47 Hz), and state entropy, SE (0.8-32 Hz, i.e. EEG). The current study evaluates the prediction probability PK of RE and SE to differentiate between consciousness and unconsciousness

Methods: Digitized EEG recordings of a previous study in 40 unpremedicated patients undergoing elective surgery [1] were replayed on a digital-analog converter and then reanalyzed with the GE Healthcare S/5 Entropy Module (GE Healthcare, Helsinki, Finland). Patients were randomly assigned to receive either propofol-remifentanil or sevoflurane-remifentanil. During induction of and emergence from anesthesia, patients were asked every 30s to squeeze the investigator's hand. Tunstall's isolated forearm technique [2] was applied while neuromuscular blocking agents were given. Loss of consciousness (LOC1) was defined as a missing response to verbal command. After intubation, drug administration was stopped until return of consciousness (ROC1), and then again continued until LOC2. At the end of surgery, ROC2 was noted. RE and SE values respectively 30s before and after LOC and ROC were used to calculate PK [3] for discrimination between consciousness and unconsciousness.

Results: PK was 0.85 for RE and 0.80 for SE in all patients. For the propofol group, PK of RE was 0.88 and PK of SE 0.83. For the sevoflurane group, PK of RE was 0.84 and PK of SE 0.78.[table1]Conclusions: The short time interval of 30s of asking patients to squeeze hand allows a clear definition of the analyzed clinical endpoints consciousness and unconsciousness during induction and emergence. With regard to this challenging study design, spectral entropy attained promising results to differentiate between consciousness and unconsciousness. RE proved to be superior to SE in both anesthetic regimes. Best results were achieved for the propofol group. PK of BIS was 0.74 with the identical data set and study design[1].

References: [1] Anesthesiology 103:934-43, 2005; [2] Br Med J 1:1321,1977; [3] Anesthesiology 84:38-51, 1996.

Anesthesiology 2006; 105: A1033
PK RE0.850.880.84
PK SE0.800.830.78
PK values for state (SE) and response entropy (RE) were calculated for all patients and both anesthetic regimens.