Prophylaxis of deep vein thrombosis in total hip replacement: which heparin and what duration?

Accessible online at: http://BioMedNet.com/karger When deep vein thrombosis is above or in a popliteal vein it is defined as a proximal deep vein thrombosis. Such thrombi have a high tendency to migrate toward the pulmonary circulation and generate an acute pulmonary embolism. Subsequently, these two entities, deep vein thrombosis and pulmonary embolism, should be considered part of the same disease, called venous thromboembolism. This pathological process is an important public health concern. The incidence has been estimated at 1/ 1,000 per year in a 25-year population-based study recently published [1]. Deep vein thrombosis is frequently clinically silent, symptoms of pulmonary embolism are not specific and there is no simple test with a high sensitivity and specificity to affirm the diagnosis of pulmonary embolism. Therefore sophisticated and/or invasive tests are necessary for the diagnosis. Even when the diagnosis of acute pulmonary embolism is accurately made and adequate therapies are initiated, the mortality related to this pulmonary vascular disease remains relatively high at about 10% [2]. For all these reasons the prevention of deep vein thrombosis is of paramount importance. One of the major risks of venous thromboembolism is orthopedic surgery. Clearly such surgery generates at least two factors of the classical Virchow triad. It produces stasis of blood and trauma to the vessel wall. Furthermore, when the endothelium is injured there is a local hypercoagulability which is the third component of the Virchow triad. These are probably the reasons why the incidence of deep vein thrombosis in the absence of prophylactic anticoagulation approaches 50% in the perioperative period of total hip replacement [3]. Thus, there is no controversy about the need for prophylaxis of deep vein thrombosis with that procedure. The means used are mechanical and/ or pharmaceutical. The mechanical approach evaluated for total hip replacement is intermittent pneumatic leg compression [4] which significantly reduced the prevalence of proximal deep vein thrombosis from 27 to 14% after total hip replacement in a randomized trial involving 310 patients. The pharmaceutical approach includes unfractionated heparin [5] which was the prophylaxis considered in the report of Manganelli et al. [6], warfarin [3], low-molecular-weight heparin [7] and a more recent drug, recombinant hirudin [8]. Low-dose unfractionated heparin is known as an effective and safe prophylaxis of deep vein thrombosis since the publication in 1975 of an international multicenter trial [5] involving more than 4,000 patients. In addition to its efficacy and safety, the advantages of such a prophylaxis are that first, it does not require laboratory monitoring and second, as pointed out by Manganelli et al. [6], its cost is low. Although low-molecular-weight heparin tends to be the standard regimen of prophylaxis of deep vein thrombosis in patients undergoing total hip replacement, low-dose unfractionated heparin is still widely used in Europe. Important questions concern the time points for starting and stopping the prophylaxis. In Europe it is recommended to start injection of unfractionated heparin or low-molecular-weight heparin from 2 to 4 h before the surgical procedure [8] whereas in North America the prophylaxis is initiated postoperatively. Concerning the cessation of the prophylaxis, there is now evidence that stop-