[The effect of positive end expiratory pressure on the blood flow velocity in the basal cerebral arteries during general anesthesia].

The effects of incremental positive end-expiratory pressure (PEEP) on middle cerebral artery (MCA) blood flow velocity and pulsatility index were studied in 20 patients scheduled for minor elective surgery. Transcranial Doppler sonography (TCD) was used to measure systolic (Vsyst) and mean flow velocity (Vmean) and the pulsatility index (PI). Heart rate (HR), mean arterial blood pressure (MAP), end-tidal CO2(PetCO2) and TCD parameters were recorded at control (PEEP = O) and following PEEP of 5 cm H2O, 10 cm H2O and 15 cm H2O for a period of 5 minutes for each PEEP level. Vsyst and Vmean were significantly reduced with each increment of PEEP. PI increased stepwise in response to each PEEP level. MAP decreased with PEEP 10 and 15 while HR and PetCO2 remained constant over time. These data suggest that PEEP-induced decreases in MCA blood flow velocity may represent decreases in CBF due to impairment of the intracranial venous flow if the diameter of the insonated vascular segment remains constant.