Abstract
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. While most centres routinely
monitor the activated clotting time and activated partial thromboplastin time (aPTT)
to assess UFH, measurement of anti-factor Xa (anti-Xa) level best correlates with
heparin dose, and appears to be 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, while the platelet function analyser
can be used in urgent situations to detect this, with a high negative predictive value.
Tests of platelet aggregation can aid in the prediction of bleeding.
To personalise management, a selection of complementary tests to collectively assess
heparin-effect, coagulation, platelet function and platelet aggregation is proposed,
to optimise clinical outcomes in these high-risk patients.
Keywords
mechanical circulatory support - thrombosis - bleeding - heparin - anticoagulation
