Background: Treatment with veno-venous extracorporeal membrane oxygenation (VV ECMO) has become a frequently considered rescue therapy in patients with severe acute respiratory distress syndrome (ARDS). Hemolysis is a common complication in patients treated with ECMO. Currently, it is unclear whether increased ECMO blood flow (Q(EC)) contributes to mortality and might be associated with increased hemolysis. Methods: A total of 441 patients with ARDS and VV ECMO, treated in a tertiary ARDS center, were included. The Q(EC) value for a significant increase in ICU mortality was determined by binary recursive partitioning. Linear regression analysis was performed to analyze a correlation between mean Q(EC) and mean plasma concentrations of cell-free hemoglobin (CFH). Results: A Q(EC) of 4 L/min divided the cohort into two groups with significantly different ICU mortality (Q(EC) <= 4 L/min: 39.3% (n = 300) versus Q(EC) > 4 L/min: 71.6% (n = 141), p < 0.001). Patients with Q(EC) > 4 L/min had a higher 28-day mortality. Furthermore, a higher mean Q(EC) was associated with increased CFH and decreased haptoglobin plasma concentrations. Conclusion: In patients with ARDS and VV ECMO, a mean Q(EC) > 4 L/min is associated with increased mortality, increased CFH and decreased haptoglobin plasma concentrations. Whether increased hemolysis determines the poorer outcome associated with higher Q(EC) should be the subject of future research.
