The Effect of Time and pH on Hemolysis During Cardiopulmonary Bypass

Objective: During cardiopulmonary bypass (CPB), the breakage of red blood cell membranes (hemolysis) and activation of humoral components (i.e. enzymes) in the blood can occur. Hemolysis and humoral component activation can lead to multiple post-operative complications (i.e. renal and lung failure). The purpose of this study is to investigate the causes of hemolysis during CPB. We hypothesize that blood damage during CPB is caused primarily by exposure of the blood to air and negative pressure during cardiotomy suction, which is used to collect blood that is lost during the operation. Methods: An in-vitro model was used to investigate the role of time and pH on hemolysis during the application of negative pressure and an air-blood interface. In the time experiment, ovine blood was exposed to pressure of -600 mmHg and room air-flow of 50 mL/min at increasing times (1, 5, 10, 15, and 30 min). In the pH experiment, ovine blood was exposed to a negative pressure of 600 mmHg, and 50 mL/min of either 25% CO 2 or room air-flow (ap proximately 0.038% CO 2 ) for ten minutes. Twenty-five percent CO 2 was used to mimic normal physiological pH. Citrate and heparin anti-coagulants were used to prevent clotting in both experimental groups. Results: Red blood cell lysis increased linearly with the time that the blood was exposed to negative pressure and air. In the pH experiment, there was no significant difference in hemolysis between the room air group and the 25% CO 2 group. Conclusion: Hemolysis during CPB is time-dependent when exposed to negative pressure and an air-blood interface. Rapid changes in blood pH do not contribute to this hemolysis.