Time-related hemolysis in stored shed mediastinal blood after cardiopulmonary bypass

Reinfusion of mediastinal shed blood during cardiopulmonary bypass reportedly reduces the need for homologous blood transfusion. Although the fragility of blood components is thought to be amplified by shear stress during cardiopulmonary bypass and processing, the time-related deterioration of red blood cells (RBCs) in stored shed blood has not been studied extensively. In this study, we examined time-related hemolysis in shed blood stored at different temperatures. We examined processed shed blood collected from 15 patients (11 men and 4 women; mean age ± standard deviation, 71 ± 9 years) during cardiopulmonary bypass. The shed blood was collected and stored at 20°C (group A) or 4°C (group B). Stored blood collected by venipuncture at the end of the surgery was used as a control. Damage was assessed by measuring its free hemoglobin (Hb) levels, using a photometric assay. The free Hb levels in blood samples from each group were tested at 0, 3, 6, 12, 24, 36, and 48 h after surgery. The free Hb levels (g/dl) at 0, 12, and 24 h were 0.03 ± 0.01, 0.05 ± 0.02*, and 0.06 ± 0.02* in group A; 0.03 ± 0.02, 0.04 ± 0.03, and 0.05 ± 0.02* in group B; and 0.01 ± 0.01, 0.01 ± 0.01, and 0.01 ± 0.01 in the control group (*p < 0.05 vs. 0 h after surgery). The free Hb levels in stored shed blood significantly increased after 12 h in group A (20°C) and increased after 24 h in group B (4°C), whereas in drawn blood, they did not significantly increase over the first 24 h. Compared to storage at 20°C, storage at 4°C suppresses the increase in the free Hb levels.