Effects of target-controlled infusion of propofol on the transient hyperaemic response and carbon dioxide reactivity in the middle cerebral artery

The transient hyperaemic response (THR) of blood flow velocity in the middl e cerebral artery (vmca), measured by transcranial Doppler ultrasonography (TCD), can be used to assess cerebral autoregulation. We have studied the e ffects of propofol administered by target-controlled infusion on vmca, THR and carbon dioxide reactivity. We studied 20 healthy adult patients undergo ing elective surgery. A standardized anaesthetic comprising alfentanil 10 m u g kg(-1), propofol via a target-controlled infusor and vecuronium 0.1 mg kg(-1) was used in both parts of the study. In the first part, THR tests we re performed on 10 subjects while awake and then at an 'induction' target c oncentration of propofol (the target at which consciousness was lost, mean 6.7 (sD 1.1) mu g ml(-1)), in the carbon dioxide study, reactivity was test ed in 10 patients while awake and at the 'induction' target concentration o f propofol by altering the end-tidal carbon dioxide partial pressure by 1 k Pa either side of baseline. Propofol caused a significant decrease in vmca but indices of autoregulation, THR ratio and strength of autoregulation inc reased significantly. Propofol had no effect on carbon dioxide reactivity. These results suggest that propofol may have a beneficial effect on cerebra l haemodynamics.