Distribution and hierarchy of regional blood flow during hypothermic cardiopulmonary bypass

BACKGROUND: Cardiopulmonary bypass (CPB) may decrease oxygen delivery relative to the nonbypass state. We predicted that a hierarchy of regional blood flow could be characterized under hypothermic (27 degrees C) CPB. METHODS: Ten pigs underwent bypass at 27 degrees C. Fluorescent microspheres were administered before and during CPB at four randomized flows: 1.9, 1.6, 1.3, and 1.0 L x min(-1) x m(-2). At completion, tissue samples were obtained from brain, renal cortex and medulla, pancreas, small bowel, and limb muscle for regional blood flow determination. RESULTS: Cerebral blood flow remained unchanged between CPB flows of 1.9 and 1.3 L x min(-1) x m(-2). Renal perfusion was stable between flows of 1.9 and 1.6 L x min(-1) x m(-2), whereas perfusion of small bowel decreased linearly with pump flow. Pancreatic perfusion was unchanged over the range of flows studied; muscle blood flow was profoundly reduced at the highest CPB flow and further decreased if pump flow was reduced below 1.6 L x min(-1) x m(-2). CONCLUSIONS: This study characterizes the organ-specific hierarchy of blood flow and oxygen distribution during hypothermic CPB. These dynamics are relevant to clinical decisions for perfusion management.