Effects of propofol on cerebral blood flow, metabolism, and cerebral autoregulation in the anesthetized pig.

We studied the effects of propofol on the cerebral circulation and flow/pressure autoregulation in eight anesthetized pigs. Regional cerebral blood flow (rCBF) was measured with a cerebral venous outflow technique. Autoregulation was tested with angiotensin infusions and gradual blocks of the caval vein for hyper- and hypotensive challenges, respectively. Propofol was given in a bolus of 2.5 mg.kg-1 followed by an infusion starting at 12 mg.kg-1.h-1 and gradually reduced to 8 mg.kg-1.h-1. As expected, propofol caused a substantial reduction in cerebral metabolic rate of oxygen, which was accompanied by an increase in cerebrovascular resistance and a decrease in CBF. In the control situation, i.e., during background anesthesia (low-dose isoflurane+nitrous oxide) only, the autoregulation was well preserved, and its lower limit was found at a mean arterial blood pressure (MABP) of 48 mm Hg. Propofol did not affect autoregulation in the group as a whole: the slope of the regression line of regional cerebrovascular resistance (rCVR) versus MABP during blood pressure reduction (caval test) was not significantly changed during propofol when compared to the control, neither was the lower limit of autoregulation (MABP, 54 mm Hg). All pigs but one followed this response pattern. The nonautoregulating pig had a completely pressure-dependent rCBF during propofol anesthesia, despite a perfectly intact auto-regulation in the control situation. It is concluded that propofol in clinical dosage does not affect autoregulation in this pig model, although individual animals may display a different response pattern.