Extracorporeal membrane oxygenation (ECMO) is utilized in critically ill neonates with severe cardiopulmonary failure. Hemolysis is a potential complication and is associated with significantly increased morbidity and mortality. The etiology of hemolysis in neonates is multifactorial, including shear forces generated by the ECMO pump, higher flow resistance from smaller tubing and smaller cannulas, the oxygenator, and other patient factors. Centrifugal pumps and oxygenators commonly have shunts with partially occluding clamps to regulate blood flow. We hypothesized that these clamps are significant contributors to hemolysis.

An in vitro study was conducted with three identical ECMO circuits containing an integrated polymethylpentene (PMP) oxygenator and centrifugal pump (Cardiohelp HLS 5.0) and 1/4″ arteriovenous (AV) loop tubing. The circuits were primed with equal components, including expired ABO-compatible packed red blood cells (pRBCs), 25% albumin, 5% albumin, sodium bicarbonate, heparin, and calcium chloride. Circuit A had a completely occluded shunt. Circuit B had a partially occluded shunt, allowing 500 mL/min of shunt flow back to the oxygenator. Circuit C had a fully open shunt, generating 1000 mL/min of shunt flow back to the oxygenator. Plasma-free hemoglobin values were measured serially over 5 days.

Baseline plasma-free hemoglobin levels were equal in all three circuits. Circuit C had the greatest increase in plasma-free hemoglobin daily (26.3 mg/dL/day) compared to Circuit A and Circuit B, which were 14.1 mg/dL/day and 12.9 mg/dL/day, respectively.

Our data suggests that partially occluding clamps are not a significant contributor to hemolysis; rather, increased flow through the oxygenator significantly increased the rate of hemolysis in neonatal ECMO circuits.