Unfractionated Heparin

This study aims to compare the accuracy of two different blood sampling methods from a central venous catheter (CVC) for measuring anti-Xa activity in children receiving unfractionated heparin (UFH) from this CVC. The results will be compared to a "gold standard" sample taken from an arterial catheter (KTA) whithout UFH. The objective is to identify a more reliable method for monitoring UFH, thereby reducing the risk of bleeding or thrombosis in these patients.