Risk factors and prevention of venous thromboembolism

In the last 20 years within the clinical research on venous thromboembolism a major objective was to identify and develop increasingly effective and safe methods of prevention. This trend is justified by the high incidence of thromboembolism as well as by the relevant mortality for acute pulmonary embolism and postphlebitic sequels of difficult treatment. A significant contribution to the rational application of methods of prevention was given by the knowledge of risk factors. Together with acquired risks, as surgery, age, malignant tumors, in the last 30 years some conditions of thrombophilia were identified. They are caused by deficiencies in coagulation inhibitors (antithrombin III, protein C, protein S) or other alteration of the anticoagulation system as resistance to activated protein C or antiphospholipid antibodies. The primary prophylaxis of venous thromboembolism is aimed at the prevention of thrombosis by pharmacologic methods able to oppose the procoagulant alterations while avoiding hemorrhagic complications. The physical methods tend to reduce the stasis in the veins of the lower extremities. Subcutaneous calcium heparin at the dose of 5000 U twice or three times a day is the most common pharmacologic method used. It was shown to be safe and effective especially in postoperative prophylaxis of venous thromboembolism in general surgery. More recently, low molecular weight heparin fractions have been introduced. As compared to standard heparin they have the advantage of a single daily dose and a better efficacy in some groups of patients, as those undergoing hip replacement. Among the substances under clinical experimentation, dermatan sulfate seems promising. Most common physical prevention methods consist in the use of elastic graduated compression stockings and systems of intermittent pneumatic calf compression. The former can be used also in presence of a hemorrhagic risk as in neurosurgery. The latter have shown a good efficacy in increasing flow velocity and probably also in enhancing the fibrinolytic activity. The combination of physical and pharmacologic methods seems to be able of enhancing the efficacy of prophylaxis.