The prevention of postoperative deep vein thrombosis and pulmonary embolism with low dose subcutaneous heparin and dextran.

The standard low dose of heparin for the prevention of deep venous thrombosis in patients who are operated upon is 5,000 units administered subcutaneously two hours before operation and at eight or 12 hourly intervals for the next seven days. Heparin in low doses can at present be recommended as an effective agent in the prevention of deep venous thrombosis in patients over the age of 40 years who are undergoing a major abdominothoracic or gynecologic operation. There is reasonable evidence that heparin in low doses also offers a satisfactory protection against fatal pulmonary embolism for patients at high risk after general abdominothoracic operations. The evidence of the effectiveness of low doses of heparin in the prevention of deep venous thrombosis is less well established in other patients and particularly those at high risk, as after urologic and hip operations. This important distinction is to be made in terms of the population at risk and the efficacy of heparin in low doses. Considering the evidence so far available, it appears that the postoperative state in which dextran has been shown to reduce the incidence of phlebographically confirmed deep venous thrombosis most convincingly is after orthopedic operations. Major orthopedic operations are precisely the type in which the superiority of heparin in low doses is controversial. Unless proved otherwise, dextran 70 in an infusion of 500 to 1,000 milliliters of a 6 per cent solution started before operation and 500 milliliters the following and next three alternate days may be the agent of choice in preventing deep venous thrombosis in major orthopedic operations. Using this scheme, the prophylaxis of postoperative deep venous thrombosis appears equally effective with dextran 70 as with oral anticoagulants. Whether the protection offered by dextran 70 will also prevent fatal and nonfatal pulmonary embolism is still an open question. Low doses of heparin and dextran do not expose patients to serious risks of bleeding after operation, and with the recommended doses of the latter drug, other untoward effects are rare. At the doses recommended, neither of these two drugs requires laboratory monitoring.