TRANSCRANIAL DOPPLER SONOGRAPHY - EFFECTS OF SEVOFLURANE COMPARED TO ISOFLURANE

Methods:Using transcranial Doppler sonography (TCD), we studied the ef fects of sevoflurane compared to equipotent doses of isoflurane on blo od-flow velocity in the middle cerebral artery (MCA) before, during, a nd after general anaesthesia. In random order, 30 patients received se voflurane (n=15) or isoflurane (n=15) given in stepwise-increasing dos es of 0.5, 1.0, and 1.5 MAC in oxygen/air (FiO(2)=0.5). Oxygen/air was then replaced by oxygen/nitrous oxide 33%/65% with decreasing doses ( 1.5, 1.0, 0.5 MAC) of sevoflurane or isoflurane. During each step, ven tilation was controlled to provide first normocapnia (end-tidal pCO(2) =38 mmHg) and then hypocapnia (end-tidal pCO(2)=27 mmHg). MCA blood-fl ow velocity and pulsatility, arterial blood pressure, heart rate, and body temperature were recorded simultaneously at the end of each perio d. For statistical analysis, within-group comparison was made by one-w ay ANOVA. Differences between groups were determined by two-way analys is of variance. Age, weight, and height of the patients were compared using Student's t-test; P<0.05 was considered significant. Results: Gr oups were comparable regarding age, weight, and height. TCD parameters were not significantly changed by increasing doses of sevoflurane or isoflurane given in oxygen/air when compared to the awake data. Howeve r, increasing MCA blood-flow velocity was found with decreasing doses of sevoflurane or isoflurane given in oxygen/nitrous oxide (P<0.05 for 0.5 MAC, normoventilation) without intergroup differences. In both gr oups, hyperventilation always decreased MCA blood-flow velocity. Concl usions: We conclude from our TCD data that equipotent doses of sevoflu rane and isoflurane comparably affect cerebral perfusion, especially w hen nitrous oxide is given simultaneously.