Authors: H. Röpcke, M.D.,* M. Könen-Bergmann,M.D.,* Th. Bouillon, M.D.,* H. Schwilden, M.D., Ph.D.°

Affiliation: * Anes. Dept., University of Bonn, D-53127 Bonn, Germany

° Anes. Dept., University of Erlangen, Germany

Volatile anesthetics elicit a concentration dependent suppression of cortical electrical activity, as measured by electroencephalography (EEG). Surgical stimulation might possibly alter the EEG due to nociceptive input, precluding the extrapolation of data from volunteers to the intraoperative situation. To obtain clinical relevant data, we examined the effect of desflurane on several univariate EEG parameters during surgery.

After having obtained institutional approval and informed consent, 12 female patients, age 33-47 yr., who underwent abdominal surgery, were included into the study. After induction of anesthesia with propofol they received desflurane as the sole anesthetic agent for maintenance. Between opening and closure of the peritoneum desflurane vapor settings were randomly varied between 0.5 and 1.6 MAC, as long as a clinically adequate depth of anesthesia was maintained. The endtidal concentration of desflurane was continuously measured (Capnomac, DATEX). Cortical activity was monitored with a 3 lead EEG, which was analyzed to yield the median and the 95% quantile of the power spectrum (SEF 95) and the bispectral index (BIS; Aspect A-1000). A sigmoid inhibitory Emax model was fitted to the concentration-EEG data. Introducing an effect compartment for desflurane significantly improved the fit.

The results of our analysis are displayed in the figure. SEF 95 and BIS decreased continuously over the observed concentration range of desflurane. SEF 95 showed no differences when compared with data from volunteers.1 Median showed a ceiling effect at concentrations exceeding 1.0 MAC. Below 0.8 MAC the concentration effect relationship was considerably steeper than that of the SEF 95. No burst suppressions were observed.

From the examined univariate EEG parameters, SEF 95 correlates best with the concentration of desflurane at the effect site. The concentration effect relationship for BIS is similar to SEF 95. The median seems to be more useful to distinguish between suppression of cortical reaction to nociceptive input and arousal reactions at inadequate levels of anesthesia.

Reference: 1. Anesthesiology 74:434-439, 1991.

Akzeptiert als Posterpräsentation auf dem "Annual Meeting of the American Society of Anesthesiologist"

20.-23.10.1997 San Diego, CA, U.S.A.