The optimal blood flow level for selective antegrade cerebral perfusion (SACP) has not been established. Based on experimental data, an arterial flow below 6 mL/kg/min may be associated with ischemia at 20 °C. To evaluate this possible ischemic threshold, cerebral metabolism was evaluated using microdialysis from the cerebral parenchyma and sagittal sinus at SACP levels of 4 and 6 mL/kg/min.
Pigs on 20 °C cardiopulmonary bypass (CPB) were assigned to Groups 1-3. In Group 1, SACP was initiated at 4 mL/kg/min and followed by 6 mL/kg/min for 60 + 60 min, respectively. In Group 2, the order was reversed from 6 to 4 mL/kg/min. Group 3 continued on CPB as controls. Cerebral near-infrared spectroscopy was measured continuously while cerebral and sagittal sinus microdialysis samples were analyzed every 30 min.
The tissue oxygenation index was significantly lower in Group 1 compared with Groups 2 and 3 at 90-120 min (p=0.007) and the cerebral lactate/pyruvate ratio was significantly greater at 120 minutes in Group 1 compared to Groups 2 and 3 (p=0.008). Glycerol in the sagittal sinus blood was significantly elevated at 120 min in Groups 1 and 2 compared to the control (p<0.0001). There was no agreement between microdialysis biomarker levels in the brain parenchyma and sagittal sinus blood.
SACP at 6 mL/kg/min preserved metabolism in the present model, whereas at 4 mL/kg/min early signs of disturbed energy metabolism were seen. Microdialysis from the sagittal sinus is feasible but no agreement with parenchymal measurements could be demonstrated.