Fortnightly review: Prophylaxis of venous thromboembolism

Introduction

The incidence of deep vein thrombosis has for years been underrated because it is difficult to diagnose accurately by clinical history and physical examination. Minimal leg symptoms may be associated with extensive venous thrombosis whereas classic symptoms and signs of pain, tenderness, and swelling of the leg can be caused by non-thrombotic disorders. In patients without symptoms and signs of deep vein thrombosis, the diagnosis is most often revealed by a pulmonary embolism; indeed, less than 20% of patients with proved pulmonary embolism have clinical features compatible with venous thrombosis in the legs.1 Thromboembolism in lower venous systems usually occurs as a complication of major surgery or of a serious illness. Without antithrombotic prophylaxis objective diagnostic measures have shown that 8-15% of patients develop venous thrombosis after major general (including abdominal) surgery, 36-60% after surgery for hip fracture, 47-57% after total hip replacement, and 40-80% after total knee replacement.2

The frequency of deep vein thrombosis is less well documented in medical patients. A recent study using colour Doppler imaging detected an unexpectedly high rate of deep vein thrombosis of 33% in patients in an intensive medical care unit; 48% of these cases were proximal leg thromboses.3 The prevalence of deep vein thrombosis will probably increase in future because the average age of the population and the number of cancer patients is increasing, high age is becoming a lesser contraindication for major surgery, and many surgical patients, young and old, are being discharged from hospital before they are fully ambulant.