[Clonidine within the scope of balanced inhalation anesthesia with sevoflurane--effects on pEEG parameters]

The anaesthetic-saving property of clonidine has often been reported. In our own prospective, randomized study, in which the depth of anaesthesia was controlled by using spectral edge frequency (target-SEF90 = 10 Hz) and clinical parameters, we confirmed the anaesthetic-saving property only for fentanyl (-20%). On the other hand, there was no difference in MAC-sevoflurane values between the groups in keeping a steady target-SEF. For this reason, we analysed the stored pEEG data with regard to clonidine-specific effects. Twenty-eight patients were included in our study. The patients were randomly treated preoperatively with an infusion of 4 micrograms/kg KG Clonidine (clonidine group) or a placebo (placebo group). For anaesthesia, a standardized procedure with fentanyl, propofol, rocuronium, N2O/O2/sevoflurane was performed. The depth of anaesthesia was controlled by using SEF90 and clinical parameters. SEF90, SEF50 and the EEG power-spectrum were analysed over a five-minute period in the steady state of anaesthesia without surgical manipulation. Both placebo and the clonidine showed comparable values for SEF90 (9.9 +/- 1 vs. 10.7 +/- 0.9 Hz). On the other hand, there were differences in the SEF50 values between the groups (3.3 +/- 0.7 vs. 6.4 +/- 2.2 Hz). In the clonidine group, relative alpha-power was higher than in the placebo group (36.3 +/- 15.8 vs. 16.8 +/- 8.8%). Parallel to this effect, there was a reduction in relative delta-power in the clonidine group (47.6 +/- 15.2 vs. 65.4 +/- 9.1%). The described EEG effects on the power-spectrum inevitably influence SEF50 and SEF90. In our opinion, SEF50 is not a powerful predictor of depth of anaesthesia, when anaesthesia is performed in the way described. By performing this variation of balanced anaesthesia and co-medication with clonidine, higher values of SEF90 (11-14 Hz) seem to be adequate for surgical manipulation.