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°C) CPB. Methods. Ten pigs underwent bypass at 27°C. Fluorescent microspheres were administered before and during CPB at four randomized flows: 1.9, 1.6, 1.3, and 1.0 L · min−1 · 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 · min−1 · m−2. Renal perfusion was stable between flows of 1.9 and 1.6 L · min−1 · 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 · min−1 · 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.