Low molecular weight heparin: An evaluation of current and potential clinical utility in surgery

Heparin, a mixture of glycosaminoglycans of various sizes, is a potent natural anticoagulant. Low molecular weight heparins (LMWH) contain only the polymers of smaller size, which appear to possess most of the antithrombotic potential. Pharmacological differences between the two suggest a number of advantages with LMWH therapy. Our objective was to establish the utility of LMWHs in comparison to the current practice of anticoagulation in surgical patients. Articles were obtained through MEDLINE and CURRENT CONTENTS queries. The searches were limited to English and French-language articles and included published overviews containing relevant individual trials. We examined the current literature, consisting of 1,730 published reports from 1979-1998, regarding the biochemistry, pharmacology, physiology, and clinical applications of LMWH in comparison with current therapy. Studies were selected based on their relevance to LMWHs, the size and methods of trials, and their application to clinical care. Peer-reviewed published data were critically evaluated by independent extraction by several authors. Established rules for levels of evidence were used to objectively evaluate the strength of evidence supporting recommendations in each clinical area. LMWHs provide superior anticoagulation in the prophylaxis of DVT following orthopedic, general, and trauma surgery. Further studies should establish which other patients may benefit from such prophylaxis. Current evidence does not support the use of LMWHs in patients with mechanical heart valves or those on mechanical cardiac support devices; however, it may have a role in the maintenance of vascular graft patency. Further studies should examine the role of LMWHs in transplant atherosclerosis, and in patients requiring long- term anticoagulation at high risk for bleeding with warfarin therapy. The economic implications of LMWH administration remain unclear. On the basis of the information presented in this review, LMWHs are promising new agents in prophylaxis and treatment of both arterial and venous thrombosis. In the near future, LMWHs are likely to supplant UFH and perhaps warfarin in many applications.