Determination of optimal perfusion flow rate for deep hypothermic cardiopulmonary bypass in the adult based on distributions of blood flow and oxygen consumption

Abstract

To determine the optimal perfusion flow in deep hypothermic cardiopulmonary bypass at 20 degrees C in human beings, we studied the relationship of perfusion flow to the whole body and to regional oxygen consumption. In adult patients (n = 11, average age 54 years) with valvular or coronary heart disease, the distributions of perfusion flow rate and oxygen consumption were analyzed by dividing into the superior and inferior vena caval areas. Measurements (n = 39) were made at various perfusion flow rates (perfusion flow rate in the superior vena caval area plus that in the inferior vena caval area equals whole-body perfusion flow rate: 0.4 to 2.2 L/min/m2) in a setting of average hemoglobin levels of 8.1 gm/dl. Between whole-body perfusion flow rate and oxygen consumption (total oxygen consumption equals superior plus inferior vena caval oxygen consumption), there was a hyperbolic correlation (r = 0.73; p less than 0.001; asymptote = 29.0 ml/min/m2). A positive linear correlation was found between whole-body perfusion flow rate and inferior vena caval oxygen consumption (r = 0.75; p less than 0.001), whereas no significant relation was seen between whole-body perfusion flow rate and superior vena caval oxygen consumption. For distributional changes in inferior vena caval perfusion flow rate/whole body perfusion flow rate and inferior vena caval oxygen consumption/whole body oxygen consumption, the broken-line regression analysis showed respective critical points where both parameters started to drop when whole-body perfusion flow rate was gradually reduced: 1.2 L/min/m2 for inferior vena caval perfusion flow rate/whole-body perfusion flow rate and 0.8 L/min/m2 for inferior vena caval oxygen consumption/whole-body oxygen consumption. The results indicate that (1) the oxygen consumption to the superior vena caval area was maintained independent of the perfusion in a relatively wide range in contrast to that for the inferior vena caval area and (2) when the redistribution of oxygen consumption is considered as undesirable under low-flow perfusion, the optimal perfusion flow for 20 degrees C deep hypothermic cardiopulmonary bypass appeared to be 0.8 L/min/m2.