Influence of Variations in Systemic Blood Flow and Blood Pressure on Cerebral Oxygenation Measured by Cerebral Oximetry

When the patient is on CPB, pressure and/or flow will be changed while continuously measuring ScO2. Temperature, CO2 , arterial oxygen content, hematocrit and anesthesia will be kept constant during the measurements. First, baseline MAP (mean arterial pressure), baseline ScO2 and baseline central venous oxygen saturation (SvO2) are determined. With the interventions, we will induce a change of 20% in MAP and/or flow. This is within the normal range during operations. Changes in blood pressure will be obtained by the use of vasoactive agents (sodiumnitroprusside for blood pressure decrease and phenylephrine for blood pressure increase). Flow is regulated by manual control of the pump flow. Values of the different variables will be obtained after a 5 min stabilisation period. Flow/pressure interventions will be randomized.