PURPOSE: Extra Corporeal Membrane Oxygenation (ECMO) is used in cases of severe 
respiratory and/or circulatory failure over periods of several days to several 
weeks. Its circuitry requires a closely monitored anticoagulation therapy that 
is empirically supported by activated clotting time (ACT)-a method often 
associated with large inter- and intraindividual variability. We aimed to 
compare the measurement of heparin activity with ACT and the direct measurement 
of the heparin activity (anti-Xa) in a large ECMO population.
METHODS: All patients treated by venoarterial or venovenous ECMO in our 
intensive care unit between January 2014 and December 2015 were prospectively 
included. A concomitant measurement of the anti-Xa activity and ACT was 
performed on the same sample collected twice a day (morning-evening) for 
unfractionated heparin adaptation with an ACT target range of 180 to 220 
seconds.
RESULTS: One hundred and nine patients (men 69.7%, median age 54 years) treated 
with ECMO (70.6% venoarterial) were included. Spearman analysis found no 
correlation between anti-Xa and ACT (ρ < 0.4) from day 1 and worsened over time. 
Kappa analysis showed no agreement between the respective target ranges of ACT 
and anti-Xa.
CONCLUSIONS: We demonstrate that concomitant measurement of ACT and anti-Xa 
activity is irrelevant in ECMO patients. Since ACT is poorly correlated with 
heparin dosage, anti-Xa activity appears to be a more suitable assay for 
anticoagulation monitoring.