Optimal tests to minimise bleeding and ischaemic complications in patients on extracorporeal membrane oxygenation

Patients supported with extracorporeal membrane oxygenation (ECMO) experience a very high frequency of bleeding and ischaemic complications, including stroke and systemic embolism. These patients require systemic anticoagulation, mainly with unfractionated heparin (UFH) to prevent clotting of the circuit and reduce the risk of arterial or venous thrombosis. Monitoring of UFH can be very challenging. Whilst most centres routinely monitor the activated clotting time and activated partial thromboplastin time (aPTT) to assess UFH, measurement of anti-Xa level best correlates with heparin dose, and appears predictive of circuit thrombosis, although aPTT may be a better predictor of bleeding. Although monitoring of prothrombin time, platelet count and fibrinogen is routinely undertaken to assess haemostasis, there is no clear guidance available regarding the optimal test. Additional tests, including antithrombin level and thromboelastography can be used for risk stratification of patients to try and predict the risks of thrombosis and bleeding. Each has their specific role, strengths and limitations. Increased thrombin generation may have a role in predicting thrombosis. Acquired von Willebrand syndrome is frequent with ECMO, contributing to bleeding risk and can be detected by assessing the von Willebrand factor activity to antigen ratio, whilst the Platelet Function Analyzer can be used in urgent situations to detect this, with high negative predictive value. Tests of platelet aggregation can aid the prediction bleeding. In order to personalise management, a selection of complementary tests to collectively assess heparin-effect, coagulation, platelet function and platelet aggregation is proposed, in order to optimise clinical outcomes in these high-risk patients.