Effects of remifentanil/propofol in comparison with isoflurane on dynamic cerebrovascular autoregulation in humans

Background: This study investigates the effects of remifentanil and propofo l in comparison to isoflurane on dynamic cerebrovascular autoregulation in humans. Methods: In 16 awake patients dynamic cerebrovascular autoregulation was me asured using transcranial Doppler sonography (TCD). Thereafter patients wer e intubated, ventilated with O-2/air (FiO(2)=0.33) and randomly assigned to one of the following anesthetic protocols: group I (n=8): 0.5 mug . kg(-1) . min(-1) remifentanil combined with a propofol-target plasma concentratio n of 1.5 mug . ml(-1); group 2 (n=8): 1.8 % isoflurane (1.5 MAC). Following 20 min of equilibration the autoregulatory challenge was repeated. Arteria l blood gases and body temperature were maintained constant over time. Stat istics: Mann-Whitney U-test and Wilcoxon signed-rank test. Results: Dynamic autoregulation was intact in all patients prior to inducti on of anesthesia expressed by an autoregulatory index (ARI) of 5.4 +/- 1.21 (mean +/- SD, group 1) and 5.9 +/- 0.98 (mean +/- SD, group 2). With remif entanil/propofol anesthesia dynamic auto-regulation was similar to the awak e state (group 1: ARI= 4.9 +/- 0.88). In contrast, autoregulatory response was delayed with 1.5 MAC isoflurane (group 2, ARI=2.1 +/- 0.92) (P <0.05). Conclusion: These data show that dynamic cerebrovascular autoregulation is maintained with remifentanil-based total intravenous anesthesia. This is co nsistent with the view that narcotics (and hypnotics) do not alter the phys iologic cerebrovascular responses to changes in MAP. In contrast, 1.5 MAC i soflurane delays cerebrovascular autoregulation compared to the awake state .