ABC of antithrombotic therapy: Venous thromboembolism: pathophysiology, clinical features, and prevention

Venous thromboembolism is a common complication among hospital inpatients and contributes to longer hospital stays, morbidity, and mortality. Some venous thromboembolisms may be subclinical, whereas others present as sudden pulmonary embolus or symptomatic deep vein thrombosis. Ultrasonic Doppler and venographic techniques have shown deep vein thrombosis of the lower limb to occur in half of all major lower limb orthopaedic operations performed without antithrombotic prophylaxis. Deep vein thrombosis of the lower limb is also seen in a quarter of patients with acute myocardial infarction, and more than half of patients with acute ischaemic stroke. Deep vein thrombosis of the lower limb normally starts in the calf veins. About 10-20% of thromboses extend proximally, and a further 1-5% go on to develop fatal pulmonary embolism. Appropriate antithrombotic measures can reduce this complication. Until recently, some clinicians were reluctant to provide such prophylaxis routinely. As unfounded fears of major bleeding complications from anticoagulant regimens wane, preventive treatments are used more often with medical and surgical patients. However, the risk of bleeding can be serious and this has particular bearing in postoperative patients. Venous thromboembolism can also arise spontaneously in ambulant individuals particularly if they have associated risk factors such as thrombophilia, previous thrombosis, or cancer. However, in over half of these patients, no specific predisposing factors can be identified at presentation. Venous thromboembolism often manifests clinically as deep vein thrombosis or pulmonary embolism, and is possibly one of the preventable complications that occur in hospitalised patients Thrombus formation and propagation depend on the presence of abnormalities of blood flow, blood vessel wall, and blood clotting components, known collectively as Virchow's triad. Abnormalities of blood flow or venous stasis normally occur after prolonged immobility or confinement to bed. Venous obstruction can arise from …