[Prevention of thrombosis with unfractionated and low molecular weight heparin].

2 or 3 daily injections of unfractionated heparin reduce the risk of thrombosis in patients undergoing general surgery from about 39 to 4 to 5% (sodium-fibrinogen-test). In patients at high risk (hip replacement, knee operations) a thrombosis incidence of about 20% is observed even under heparin prophylaxis. The clinical incidence of venous thrombosis is reduced to less than 1% in patients undergoing general surgery. Low molecular weight heparins have been investigated in a number of clinical trials. A single daily s.c. injection of low molecular weight heparin is as effective or more effective than 2 to 3 daily s.c. injections of unfractionated heparins in the prevention of thromboses in general surgery. The bleeding risk is not reduced compared to unfractionated heparin. Most frequent side effects of heparin prophylaxis are bleeding complications followed by thrombocytopenia between 1 to 2% and the rare but dangerous "white-clot-syndrome" (less than 0.01%). Some patients with thrombocytopenia or white-clot-syndrome can be successfully treated with a low molecular weight heparin fraction.