Background: Haemolysis results from excess erythrocyte trauma and is common in ex-vivo normothermic machine perfusion systems. Pump design is hypothesised to be a major contributor of excess erythrocyte trauma within ex-vivo machine perfusion systems. This study aimed to compare haemolysis between two pump designs, peristaltic and diaphragmatic, in a low-flow perfusion model.

Methods: Red-cell based perfusate was simultaneously circulated through two perfusion systems. Both perfusion systems had identical tubing, reservoir, and water-bath, but varied according to pump design (peristaltic or diaphragmatic pump). The perfusate was circulated at 25 mL/min and 10 – 15 mmHg pressure at 37.5 degrees for 24 hours. Samples were collected at 0, 2, 4 and 24 hours of perfusion for blood gas analysis and plasma free haemoglobin.

Results: Haemoglobin was not significantly different between groups at 2, 4, and 24 hours (p > 0.05 for all time points). Plasma free haemoglobin was significantly lower in the peristaltic pump group at 2-hours (21.4 vs 120.9 mg/ dL, p = 0.043), 4-hours (25.3 vs 129.8 mg/ dL, p = 0.021) and 24-hours of perfusion (107.8 vs 222.1 mg/ dL, p = 0.003) than the diaphragmatic pump group.

Conclusions:  Haemolysis was present in all groups and increased during 24 hours of perfusion. Perfusate samples in the diaphragmatic pump group had significantly higher haemolysis at all time points than perfusate samples in the peristaltic pump group. This suggests that diaphragmatic pumps may have greater sheer forces at low-flow rates than previously hypothesised.