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The aim of this study was to determine the effects of desflurane, at 1 and 1.5 MAC, on cerebral autoregulation. Data were analysed from eight patients undergoing non-neurosurgical procedure. The blood flow velocity in the middle cerebral artery was measured by transcranial Doppler ultrasound and cerebral autoregulation was assessed by the transient hyperaemic response test. Partial pressure of the end-tidal carbon dioxide (PE'(CO(2))) and mean arterial pressure were measured throughout the study. Anaesthesia was induced with propofol and was maintained with desflurane at end-tidal concentrations of 7.4% (1 MAC) or 10.8% (1.5 MAC). The order of administration of the desflurane concentrations was determined randomly and a period of 15 min was allowed for equilibration at each concentration. The transient hyperaemic response tests were performed before induction of anaesthesia and after equilibration with each concentration of desflurane. An infusion of phenylephrine was used to maintain pre-induction mean arterial pressure and ventilation was adjusted to maintain the pre-induction value of PE'(CO(2)) throughout the study. Two indices derived from the transient hyperaemic response test (the transient hyperaemic response ratio and the strength of autoregulation) were used to assess cerebral autoregulation. Desflurane resulted in a marked and significant impairment in cerebral autoregulation; at concentrations of 1.5 MAC, autoregulation was almost abolished.