The Relationship Between Membrane Oxygenator Blood Path Pressure Drop and Hemolysis: An In-vitro Evaluation

Plasma hemoglobin (pl-Hgb) production was measured for the Bard HF-5000 (n = 4), Sarns SMO (n =4) and Sarns Turbo (n =4) membrane oxygenators (MO), which were tested on separate closed-loop roller pump circuits to compare differences in hemolysis production as a function of pressure drop (P). The three oxygenators were selected because of their varied P characteristics. Circuits were prepared by clamping off the MO and then priming with freshly drawn, heparinized, filtered bovine blood that had an adjusted hemoglobin (Hgb) of 8.0 g/dL. Roller pump occlusions were set using a pressure transducer. To correct for hemolysis resulting from the roller pump in each oxygenator circuit, the blood was pumped through a bypass line around each MO for the first 90 minutes of each study. Blood flows were maintained at 4.0 L/min at a pressure of 200 mmHg and tests for pl-Hgb conducted at 30-minute intervals. Blood was then circulated through each MO for 180 minutes at outlet pressures of 200 mmHg. Total pl-Hgb values were corrected for flow and time in order to calculate a hemolysis index (HI) in grams of pl-Hgb generated per 100 L of blood pumped. A weak correlation was demonstrated between P and HI (r = 0.69). This study suggests that variances in MO hemolysis are a function of design variables, such as membrane surface area, prime volume, and blood path length, rather than of P. The pl-Hgb generated from each MO was negligible when compared with typical pl-Hgb levels generated during routine cardiopulmonary bypass.