How can clotting of the dialyzer be prevented?
The contact of blood with the extracorporeal circuit, lines, and membrane activates platelets and the production of a variety of inflammatory and prothrombotic mediators.
The result is the induction of fibrin deposition and filter clotting.
Clotting of the dialyzer reduces its longevity, and, more importantly, reduces the efficiency of solute clearance. Inefficient anticoagulation reduces the dialyzer performance by diminishing the surface of the membrane available for diffusion or convection.
The anticoagulation for RRT can be systemic or regional, when only the dialysis circuit is anticoagulated. Systemic anticoagulation with unfractionated heparin is the most commonly used method.
Heparin is usually administrated as a bolus, followed by a continuous infusion into the arterial line. The optimal dose for AKI patients is not established.
The target is to maintain a partial thromboplastin time of 1.5 to 2 times the normal level. The use of low-molecular-weight heparin (LMWH) requires the monitoring of factor Xa levels. In patients at high risk of bleeding, systemic anticoagulation should be avoided. Although IHD can often be performed without anticoagulation, using intermittent saline flushes (100 cc) every 15 to 30 minutes in the arterial line could improve the circuit and filter life. In CRRT, regional anticoagulation with citrate is the alternative method.
Citrate is infused continuously in the arterial line and chelates the free calcium in the circuit, inhibiting the coagulation cascade. Part of the complex calcium citrate is removed by dialysis clearance and part is metabolized in the liver. Serum calcium concentrations (preferably ionized) should be monitored, and continuous or intermittent calcium infusion performed as necessary.
The use of regional citrate anticoagulation (RCA) increases the buffer load during the treatment as citrate is converted to bicarbonate in the liver. The possibility of metabolic alkalosis requires modifications in the hemofiltration solution or dialysate.