Hematological effects of a low-prime neonatal cardiopulmonary bypass circuit utilizing vacuum-assisted venous return in the porcine model.

Limiting hemodilution in neonates is difficult when extracorporeal circuits require priming volumes that are 2 to 3 times the blood volume of the newborn patient. This extreme hemodilution contributes to the development of significant postbypass coagulation disturbances. The purpose of this project was to design a low-prime neonatal bypass circuit and evaluate the coagulation status after reduced hemodilution. The null hypothesis stated there is no significant difference in the measured coagulation parameters between the low-prime circuit and the standard high-prime circuit. Four neonatal piglets (2-4 kg) were divided into two groups and placed on cardiopulmonary bypass using either a low- (200 ml) or high-prime (500 ml) circuit. Both groups were cooled to 20 degrees C, and, following cardioplegic arrest, underwent circulatory arrest for 20 minutes. The low-prime circuit used vacuum-assisted venous drainage, which permitted the circuit to be at the patient level. The high-prime circuit required fresh washed donor red blood cells to maintain the hematocrit in the desired range of 15-20%. The platelet count on bypass decreased by 60 +/- 1.0% in the low-prime group versus 79.6 +/- 0.1% in the high-prime group. Following bypass, the platelet count was reduced by 38.3 +/- 14.3% in the low-prime versus 60.2 +/- 2.6% in the high-prime group. During rewarming, the mean heparinase activated clotting time (ACT) increased 5.1% above baseline in the low-prime group and 53.5% above baseline in the high-prime group. Mean plasma-free hemoglobin levels increased 40.4 mg/dl in the low-prime group versus 62.1 mg/dl in the high-prime group during bypass. This laboratory evaluation of a low-prime neonatal circuit demonstrates that coagulation disturbances often present in neonates can be reduced with the use of a low-prime circuit.