Risk factors of system clotting in heparin-free haemodialysis

Heparin-free haemodialysis must be considered for all dialysis patients with a risk of haemorrhage. This technique is associated with increased danger of system coagulation with a blood loss of up to 250 ml. In 84 patients with a risk of haemorrhage, 296 heparin-free haemodialyses were recorded prospectively. First signs of coagulation were found very much more frequently in the venous airtrap than in the dialyser (146 vs 42). System coagulation occurred in 13 of the 296 dialyses (4%) and was prevented by prophylactic switching of the system and dialyser in 140 dialyses (47%). The time of system coagulation was on average 1.8 hours (+/- 0.2) after the beginning of dialysis. The 13 patients with system coagulation had a reduced blood flow on dialysis (217 +/- 52 vs 240 +/- 36 ml/min). Their initially normal clotting time (12 +/- 5 vs 14 +/- 4 min) was more significantly shortened after 2 h (4 +/- 3 vs 8 +/- 3 min). The activities of antithrombin III (87 +/- 34% vs 88 +/- 39%) and protein C (66 +/- 45% vs 59 +/- 37%) do not differ from those of 47 other patients, even at the time of system coagulation, as measured in five patients (92 +/- 34% for antithrombin III, 51 +/- 29% for protein C). System coagulation and shortening of clotting time thus cannot be regarded as a consequence of absorption of these inhibitory factors of plasmatic coagulation. The danger of system coagulation in heparin-free haemodialysis could probably be further reduced by an improvement of the biocompatibility of systems (airtrap) and dialysers (less activation of thrombocytes).