The effects of sevoflurane and nitrous oxide on middle cerebral artery blood flow velocity and transient hyperemic response

We studied the effects of sevoflurane, with and without nitrous oxide, on t he indices of cerebral autoregulation (transient hyperemic response ratio a nd the strength of autoregulation) derived from the transient hyperemic res ponse (THR) test. Twelve patients (ASA physical status I or II) aged 18-40 yr: presenting for routine nonneurosurgical procedures were recruited. The middle cerebral artery blood flow velocity was continuously recorded using transcranial Doppler ultrasonograyhy. Preinduction THR tests were performed before the patients were anesthetized with alfentanil, propofol, and vecur onium. End-tidal carbon dioxide concentration and mean arterial pressure (t o within 10% with a when phenylhrine infusion) were maintained at their pre induction values. THR tests were performed sequentially at the following en d-tidal sevoflurane concentrations: 2.2% in oxygen, 3.4% in oxygen, 3.4% wi th 50% nitrous oxide in oxygen, and 2.2%; with 50% nitrous oxide in oxygen. Neither 2.2% nor 3.1%; sevoflurane significantly affected cerebral autoreg ulation The addition of 50% nitrous oxide to the 2.2%, but not the 3.4% b, concentration of sevoflurane increased middle cerebral artery blood flow ve locity and decreased autoregulatory indices significantly. Implications: Tr ansient hyperemic response is preserved during sevoflurane anesthesia but i s significantly impaired when nitrous oxide is added to the lower concentra tion of sevoflurane (2.2%). These findings have implications for neurosurgi cal patients undergoing general anesthesia.