HP and acute respiratory distress syndrome: 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.