In patients undergoing VV-ECMO for severe ARDS, indirect signs of hemolysis such as plasma levels of COHb and haptoglobin show an association with pulmonary and SVR; COHb levels during ECMO before VAP independently predict VAP; both COHb and haptoglobin levels during ECMO independently predict mortality; the iron pathway is associated with VAP onset (ie, transferrin levels before ECMO) and mortality (ie, iron levels before ECMO) after adjustment for major confounders in multivariable models. The gene discussed is TF; the disease is acute respiratory distress syndrome.