Extracorporeal membrane oxygenation (ECMO) can be life-saving, but suffers from thrombus formation in the circuit with associated risks of oxygenator occlusion, hemolysis and arterial embolism. The formation of thrombin is the key step to thrombus formation and two factors are needed for sustained thrombin generation, a coagulation activator to initiate the process and a procoagulant phospholipid surface for the coagulation system to assemble on.
Materials and methods
The purpose of this study was to use thrombin generation potential (TGP) and other assays to determine the specific coagulation activators and sources of procoagulant phospholipid that are present in ECMO patient plasma. Samples were collected from 60 patients on ECMO (age 1d-19y) followed evaluation of native and stimulated TGP, measurement of factor II levels and determination of procoagulant extracellular vesicle levels by flow cytometry.
During ECMO, native (unstimulated) TGP was increased, followed by a decrease back towards normal after ECMO ended. The main activator of TGP in ECMO plasma was increased FXIa (100% of samples tested), while increased tissue factor activity was present in 7%. Procoagulant phospholipids were present in plasma from ECMO patients in the form of circulating platelet and red cell extracellular vesicles, which were increased 2 to 7-fold compared to normal. Procoagulant extracellular vesicle levels correlated with increased plasma native TGP activity.
ECMO activates coagulation in plasma primarily through activation of the contact system and formation of activated factor XIa and generation of circulating procoagulant extracellular vesicles through platelet and red cell activation.