Optimal anticoagulation strategy in haemodialysis with heparin-coated polyacrylonitrile membrane

Binding of polycationic unfractionated heparin onto the modified AN69 polyacrylonitrile membrane, whose surface electronegativity has been neutralized by layering polyethyleneimine (AN69ST), produces stable coating. We investigated whether the heparin-coated membrane was suitable for regular haemodialysis with low heparin doses.

Sheep were instrumented for extracorporeal circulation perfusing a dialyser equipped with either the AN69ST or the original AN69 membrane. Dialysis sessions were performed after priming the dialyser with heparinized saline. The session was conducted without systemic administration of heparin. In chronic haemodialysis patients, the AN69ST membrane was tested for safety, clotting and thrombin generation according to protocols of 4-h haemodialysis sessions with tapered heparin doses. The goal was to define optimal heparin requirements with the heparin-coated membrane in the setting of continuous or intermittent administration of heparin. Both unfractionated and low molecular weight heparin (LMWH) (enoxaparin) were tested.

In sheep, systemic heparin-free haemodialysis was conducted for 6 h without clotting using the heparin-coated dialyser. In the same conditions, massive clotting was observed within 90 min of dialysis with the native AN69 membrane. In man, through kinetic measurements of activated partial thromboplastin time (APTT), heparin anti-Xa concentration and thrombin-anti-thrombin complexes levels (TAT), significant dialyser clotting was avoided when APTT and anti-Xa concentration at 180 min of dialysis, were maintained at >40 s and >0.2 IU/ml, respectively. With the AN69ST heparin-coated membrane, thrombin generation was reduced then suppressed, as compared with the original AN69, primed in the same conditions. Safety of haemodialysis conducted with the AN69ST heparin-coated membrane and low doses of unfractionated heparin (50% reduction of the reference dose) was validated by a survey of 2590 sessions in 32 patients. Doses of LMWH were also safely reduced by 50%. In addition, haemodialysis without systemic administration of heparin was possible with minor risk of clotting.

During the rinsing phase, the ionic interactions between the new AN69ST polyacrylonitrile membrane and unfractionated heparin induce stable heparin coating. This allows a significant reduction of systemic anticoagulant requirements without increasing the risk of clotting, both in the experimental setting and in the chronic haemodialysis patients. Further studies are required to assess this advantage in patients with acute renal failure and at risk of bleeding and to reduce the metabolic consequences of long-term treatment with heparin.