Hematologic observations made in patients with acute respiratory distress syndrome in the cooperative ECMO project

In a recently completed three-year multicenter trial, 90 individuals with adult acute respiratory distress syndrome (ARDS) were randomly allocated to conventional therapy with or without long-term extracorporeal membrane oxygenation (ECMO). This study conclusively demonstrated that ARDS is associated with frequent major bleeding and thrombotic episodes and that the bleeding correlates best with the degree of thrombocytopenia and is enhanced by the machine. Neither heparin's therapeutic efficacy nor its ability to increase bleeding could be proven. ARDS is associated with a complex coagulation disturbance. Besides thrombocytopenia, there were lowered circulating levels of factors VII and XII which may be related to changes in the pulmonary endothelium. ECMO was associated with relative leukopenia and a marked shift to immature circulating leukocytes. Further studies are needed to better define the clinical importance of thrombosis and bleeding in the lung, the role for heparin in treatment, and the meaning of reductions in coagulation factors in defining the course, prognosis and response to therapy of patients with ARDS.