Comparison of the Best Method for Measuring Anti-Xa Activity in Children Receiving Unfractionated Heparin in Cardiac Intensive Care (COMPAXE-HNF)

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.

* Scientific Justification: UFH is widely used in pediatric cardiac intensive care for its short half-life and availability of an antidote. However, monitoring its effect via anti-Xa activity is challenging. The standard method of sampling from a CVC is known to be prone to heparin contamination, leading to inaccurate results (over- or under-anticoagulation). This lack of precision can lead to dangerous complications like major bleeding or thrombotic events. As studies by Palermo et al. (1980) and Bauman et al. (2012) have shown, the unreliability of CVC samples justifies the search for a safer alternative. The arterial catheter (KTA) provides a contamination-free "gold standard," making it the ideal comparison for evaluating the more reliable sampling method. * Procedure: The study will compare two CVC sampling methods (a standard flush protocol and a new experimental method) against the gold standard (KTA sampling without UFH) * Follow-up: The study will be conducted over three consecutive days. Each day, three sets of blood samples will be collected every 6 hours per patient (KTA, standard CVC, and experimental CVC).