ObjectiveTo evaluate the correlation of activated partial thromboplastin time (aPTT), activated clotting time (ACT) and the activity of anti-factor Ⅹa activity with the concentration of unfractionated heparin (UFH) during extracorporeal membrane oxygenation (ECMO) in children after cardiac surgery.MethodsThe clinical data of children (aged 6 months to 6 years) who received ECMO support after cardiac surgery in Fuwai Hospital from January 2010 to October 2020 were retrospectively collected. And the aPTT value, ACT value, anti-Ⅹa activity and the corresponding UFH dose measured simultaneously during ECMO were recorded. According to the Extracorporeal Life Support Organization anticoagulation guideline, the bleeding events of children during ECMO support were defined, and the children were divided into a bleeding group and a non-bleeding group according to whether bleeding events occurred. Pearson correlation was used to evaluate the correlation between ACT, aPTT or anti-Ⅹa activity and UFH in the same patient.ResultsA total of 58 children, including 33 males and 25 females, aged 27.31±34.17 months, were enrolled and divided into the bleeding group (n=39) and the non-bleeding group (n=19). Univariate analysis showed that compared with children in the non-bleeding group, children in the bleeding group had lower red blood cell counts (P=0.049), hemoglobin concentration (P=0.010), and hematocrit (P=0.046) on the day of ECMO installation. In addition, the transfusion volume of fresh frozen plasma (P=0.034) and fibrinogen (P=0.033) in the bleeding group was relatively more, and the proportion of exploratory thoracotomy for hemostasis was high (P=0.000); there was a moderate degree of correlation between anti-Ⅹa and UFH (r=0.418, P=0.013) but there was no correlation between ACT or aPTT and UFH.ConclusionThe aPTT value and ACT value are poorly correlated with the concentration of UFH transfused during ECMO in children after cardiac surgery, while the anti-Ⅹa activity is moderately correlated with it.