[Transcranial doppler sonography. Effect of sevoflurane in comparison to isoflurane]

Using transcranial Doppler sonography (TCD), we studied the effects of sevoflurane compared to equipotent doses of isoflurane on blood-flow velocity in the middle cerebral artery (MCA) before, during, and after general anaesthesia. In random order, 30 patients received sevoflurane (n = 15) or isoflurane (n = 15) given in stepwise-increasing doses of 0.5, 1.0, and 1.5 MAC in oxygen/air (FiO2 = 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, ventilation was controlled to provide first normocapnia (end-tidal pCO2 = 38 mmHg) and then hypocapnia (end-tidal pCO2 = 27 mmHg). MCA blood-flow velocity and pulsatility, arterial blood pressure, heart rate, and body temperature were recorded simultaneously at the end of each period. For statistical analysis, within-group comparison was made by one-way ANOVA. Differences between groups were determined by two-way analysis of variance. Age, weight, and height of the patients were compared using Student's t-test; P < 0.05 was considered significant.

Groups 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. However, 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 groups, hyperventilation always decreased MCA blood-flow velocity.

We conclude from our TCD data that equipotent doses of sevoflurane and isoflurane comparably affect cerebral perfusion, especially when nitrous oxide is given simultaneously.