Impact of Pump Flow Rate During Selective Cerebral Perfusion on Cerebral Hemodynamics and Metabolism

Background. Although hypothermic selective cerebral perfusion (SCP) is widely used for cerebral protection during aortic surgery, little is known about the ideal pump-flow management during this procedure. This study explored cerebral hemodynamics and metabolism at two different flow rates. Methods. Fourteen pigs (33 to 38 kg) were cooled on cardiopulmonary bypass to 25 degrees C. After 10 minutes of hypothermic circulatory arrest, the animals were randomly assigned to 60 minutes of SCP at two different pump flow rates: 8 mL . kg(-1) . min(-1) (n = 7) and 18 mL . kg(-1) . min(-1) (n = 7). Microspheres were injected at baseline, coolest temperature, and at 5, 15, 25, and 60 minutes of SCP to calculate cerebral blood flow, cerebral vascular resistance, metabolic rate, and intracranial pressure. Results. Cerebral blood flow decreased during cooling to 41% of the baseline value (from 57 +/- 10 to 23 +/- 4 mL . min(-1) . 100 g(-1)). It recovered during the initial 15 minutes of SCP, showing a significantly higher increase (p = 0.017) at high-flow versus low-flow perfusion (139 +/- 41 versus 75 +/- 22 mL . min(-1) . 100 g(-1)). After 60 minutes of SCP the cerebral blood flow almost returned to baseline values in the low-flow group (43 +/- 25 mL . min(-1) . 100 g(-1)), but showed an unexpected decrease (30 +/- 7 mL . min(-1) . 100 g(-1)) in the high-flow group. The highest regional cerebral blood flow was seen in the cortex (66 +/- 12 mL . min(-1) . 100 g(-1)), followed by the cerebellum (63 +/- 12 mL . min(-1) . 100 g(-1)), the pons (51 +/- 17 mL . min(-1) . 100 g(-1)), and the hippocampus (36 +/- 9 mL . min(-1) . 100 g(-1)). Intracranial pressure increased from 11 +/- 3 to 13 +/- 5 mm Hg during cooling on cardiopulmonary bypass. During low-flow SCP, it stayed stable at baseline values, whereas high-flow perfusion resulted in significantly higher intracranial pressures (17 +/- 3 mm Hg; p = 0.001). Changes in cerebral vascular resistance and metabolic rate showed no significant differences between the groups. Conclusions. High-flow SCP provides no benefit during long-term SCP at 25 degrees C. Higher cerebral blood flow during the initial SCP period leads to cerebral edema, with no profit in metabolic rate. (Ann Thorac Surg 2010;90:1975-84) (C) 2010 by The Society of Thoracic Surgeon