Summary Summary: Extracorporeal circuits in the intensive care unit cause an imbalance in the coagulation system leading to activation of procoagulant factors. In order to avoid clotting in the circuit, anticoagulants are generally administered. The standard substance is unfractionated heparin. For patients with heparininduced thrombocytopenia, recombinant hirudin is the drug of choice. Alternatively, danaparoid sodium may be used. Prostacyclin and sodium citrate (regional administration) are substances which will be given only very rarely.