Whole-body oxygen consumption during low-flow hypothermic cardiopulmonary bypass

To assess the adequacy of tissue perfusion during low-flow, moderately hypothermic cardiopulmonary bypass (CPB), we measured whole-body oxygen consumption (VO2), serum lactate concentrations, and acid-base balance in 12 men undergoing myocardial revascularization. When perfusion flow rate was kept at control levels (2.1 L/min/m2), decreasing the patient's body temperature to 25.4 +/- 1.8 degrees C (mean +/- SD) was associated with a reduction in VO2 of almost 50% (from 83.3 +/- 14.6 ml/min/m2 to 45.6 +/- 9.6 ml/min/m2, p less than 0.001). Subsequent lowering of flow rate by nearly half (from 2.1 to 1.2 L/min/m2) under these moderately hypothermic conditions failed to alter VO2, which was measured several times over a 40 minute period. Although small increases in base deficit occurred during hypothermia, acidosis did not occur after reductions in flow rate. Serum lactate levels were not affected by changes in either temperature or flow rate. We conclude that a perfusion flow rate as low as 1.2 L/min/m2 does not compromise tissue perfusion during CPB with moderate systemic hypothermia and cardioplegic arrest.