Hemodialysis and continuous renal replacement therapies require extracorporeal blood flow. Some form of anticoagulation, usually with heparin, is required to prevent thrombosis in the blood circuit. Strategies to minimize the risk of bleeding include low-dose or "minimum heparin" as well as fast-flow "no-heparin" methods. Regional anticoagulation with citrate, prostacyclin, as well as heparin-protamine have also been used. The bleeding tendency induced by these regimens is additive to the commonly present platelet dysfunction associated with advanced renal failure. (See "Platelet dysfunction in uremia".)
Anticoagulation during hemodialysis can be monitored by the determination of activated clotting times (ACTs). However, although ACTs have advantages over whole blood clotting times in that they are interpreted by an automated method with rapid results, they are infrequently used because of quality assurance and regulatory issues.
In general, most outpatient dialysis units do not routinely measure anticoagulation parameters, unless there is an issue with dialyzer clotting or prolonged bleeding following dialysis. Usually each dialysis unit has a protocol that is followed.
Anticoagulation in routine hemodialysis consists of a standard dose of heparin given as a bolus at the start of the dialysis treatment, with a mid-treatment dose to maintain suitable anticoagulation. Alternatively, heparin modeling can be performed using an initial bolus followed by a constant fixed infusion of heparin to maintain an activated clotting time (ACT) of 200 to 250 seconds (normal = 90 to 140 seconds).
The ACT (activated whole blood clotting time) is performed by addition of an activating agent (eg, celite, kaolin) to a sample of freshly drawn whole blood and measuring the time (in seconds) for formation of a clot. (see "Clinical use of coagulation tests", section on 'Activated whole blood clotting time'). This therapy ensures systemic anticoagulation throughout the dialysis treatment. It is reliable and requires minimal staff intervention after a patient's heparin dose is determined (based on ACT goal).