Coagulation disorders are one of the most common complications in critically ill patients. Among them deep vein thrombosis and pulmonary embolism are the most significant factors increasing morbidity and mortality in ICU patients. Use of anticoagulant prophylaxis aims to prevent these dangerous complications. Most commonly used anticoagulant prophylaxis agents are low molecular weight heparins (LMWH). LMWH therapeutic efficiency is measured with activity of anti-Xa factor, that should range between 0.2 and 0.4 IU/mL in order to prevent thrombotic complications. Due to grave general condition, critically ill patients may often develop acute kidney injury (AKI), that requires renal replacement therapy (RRT). Because of haemodynamic instability the safest therapeutic choice seems to be continuous veno-venous hemodiafiltration (CVVHDF). This RRT mode removes particles in the size of few daltons even up to 10 kilodaltons (kDa) such as metabolic product waste, ions, hormones etc. LMWH with average molecular weight of 4.5 kDa and fondaparinux with average molecular weight of 1.7 kDa may be removed during CVVHDF resulting in insufficient activity of anti-Xa factor thus increasing the risk of thrombotic complications in critically ill patients.
Dose of anticoagulant prophylaxis in patients with continuous veno-venous hemodiafiltration may be insufficient to keep anti-Xa factor activity in prophylactic range.