Activated Clotting Time for Heparin Dosage Monitoring in Continuous Arteriovenous Hemofiltration

Abstract

The main purpose of heparinization in continuous arteriovenous hemofiltration (CAVH) is to prevent the hemofilter from clotting without having to systemically anticoagulate the patient. As with any extracorporeal circuit, when blood comes in contact with a foreign surface, protein is absorbed within milliseconds and platelet adhesion occurs. The more fibrinogen that attaches to the circuit, the greater the affinity for platelets. When platelets attach to the surface, they activate more platelet adhesion which leads to fibrin formation if there is no heparin in the system [1]. The anticoagulant heparin prevents clot formation by increasing the action of antithrombin-III, an inhibitor of thrombin, and therefore inhibits the conversion of fibrinogen to fibrin. Thrombin inhibition is dose related and heparin is rapidly metabolized, thus the heparin effect can be titrated to any desired level by adjusting a continuous infusion. Our approach to anticoagulation with CAVH is derived from the method of Kramer [2], combined with our experience with prolonged extracorporeal circuits like ECMO [3].