Contemporary oxygenator design relative to hemolysis

Hemolysis is a well-known phenomenon during cardiovascular surgery and generally attributed to cardiopulmonary bypass, particularly when using high-resistant oxygenators. This study aimed at investigating whether transoxygenator pressure drop can be considered an independent factor of hemolysis. Additionally, intraoxygenator blood distribution and shear stress were assessed. A low-resistant (LR, n = 3), a moderate-resistant (MR, n = 3), and a high-resistant (HR, n = 3) clinically used membrane oxygenator were tested in vitro using a roller pump and freshly drawn heparinized porcine blood. Flow rates were set to 2 and 4 L/min and maximum flow compliant to the oxygenator type for 1 hour each. As a control, the oxygenator was excluded from the system. Blood samples were taken every 30 minutes for plasma-free hemoglobin assay and transoxygenator pressure was measured inline. Intraoxygenator blood distribution was assessed using an ultrasound dilution technique. Despite the relatively broad spectrum of pressure drop and resultant transoxygenator pressure drops (LR: 14-41 mmHg, MR: 29-115 mmHg, HR: 77-284 mmHg, respectively), no significant association (R2 = .074, p = .22) was found with the normalized index of hemolysis. The shear stress of each oxygenator at maximum flow rate amounted to 3.0 N/m2 (LR), 5.7 N/m2 (MR), and 8.4 N/m2 (HR), respectively. Analysis of blood flow distribution curves (kurtosis and skewness) revealed intraoxygenator blood flow distribution to become more homogeneous when blood flow rates increased. Contemporary oxygenators were shown not to be a predominant factor for red blood cell damage.