DYNAMIC AND STATIC CEREBRAL AUTOREGULATION DURING ISOFLURANE, DESFLURANE, AND PROPOFOL ANESTHESIA

Background: Although inhalation anesthetic agents are thought to impair cerebral autoregulation more than intravenous agents, there are few controlled studies in humans. Methods: In the first group (n = 24), dynamic autoregulation was assessed from the response of middle cerebral artery blood now velocity (Vmca) to a transient step decrease in mean arterial blood pressure (MABP), The transient hypotension was induced by rapid deflation of thigh cuffs after inflation for 3 min, In the second group (n = 18), static autoregulation was studied by observing Vmca in response to a phenylephrine-induced increase in MABP, All patients were studied during fentanyl (3 mu g . kg(-1). h(-1))/nitrous oxide (70%) anesthesia, followed by, in a randomized manner, isoflurane, desflurane, or propofol in a low dose (0.5 MAC or 100 mu g . kg(-1). min(-1)) and a high dose (1.5 MAC or 200 mu g . kg(-1). min(-1)), The dynamic rate of regulation (dROR) was assessed from the rate of change in cerebrovascular resistance (MABP/Vmca) with the blood pressure decreases using computer modeling, whereas the static rate of regulation (sROR) was assessed from the change in Vmca with the change in MABP. Results: Low-dose isoflurane delayed (dROR decreased) but did not reduce the autoregulatory response (sROR intact), Low-dose desflurane decreased both dROR and sROR, During 1.5 MAC isoflurane or desflurane, autoregulation was ablated (both dROR and sROR impaired), Neither dROR nor sROR changed with low- or high-dose propofol. Conclusions: At 1.5 MAC, isoflurane and desflurane impaired autoregulation whereas propofol (200 mu g . kg(-1). min(-1)) preserved it.