Rationale for the use of a low molecular weight heparin during hemodialysis with polysulphone membrane in uremic patients

We carried out an open, randomized, cross-over study to test the rationale for use of a low molecular weight heparin during hemodialysis with polysulphone membranes. Ten uremic patients (6 men, 4 women, mean age 50 ± 11 years, range 31-70) in chronic hemodialysis underwent paired filtration dialysis with either low molecular weight heparin or unfractionated heparin, then crossed over to the other anticoagulant treatment. We measured the following: anti-factor Xa and anti-factor IIa activity in patients' plasma and in the ultrafiltrate, activated partial thromboplastin time and bleeding time before, during and after hemodialysis. Some low molecular weight fractions of heparin were lost in the ultrafiltrate during hemodialysis, while higher molecular weight fractions were retained. The activated partial thromboplastin time during dialysis and the bleeding time after dialysis were more prolonged with unfractionated heparin than with the low molecular weight heparin (p <0.01 and p <0.05 respectively). Our data indicate that the use of a low molecular weight heparin determines a less pronounced prolongation of the activated partial thromboplastin time during dialysis and prevents a post-dialytic increase in bleeding time.