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  1. Grace V Robinson (gracevrobinson@yahoo.co.uk), specialist registrar
  1. Department of Respiratory Medicine, Royal Berkshire and Battle Hospitals NHS Trust, Reading RG1 5AN
  • Accepted 10 October 2005

A pulmonary embolism is an obstruction of part of the pulmonary vascular tree, usually caused by a thrombus that has travelled from a distant site—for example, the deep veins in the leg. The annual incidence is 60-70 per 100 0001 w1; it is a common cause of breathlessness and pleuritic pain.

Pulmonary embolism has an untreated mortality of about 30% and is the commonest cause of death after elective surgery (accounting for up to 15% of all post-operative deaths).2 w2 It is the commonest cause of maternal death in the United Kingdom.3

Who gets it?

Most thrombi are generated in the deep venous system of the lower leg and pelvis. Venous stasis is increased by immobility and dehydration, which leads to the accumulation of clotting factors and platelets. Up to 50% of leg thrombi embolise; clots above the knee do so more commonly than clots below the knee.4 w3 Large clots may lodge at the bifurcation of the main pulmonary arteries, causing haemodynamic compromise. Smaller clots travel more distally, infarcting the lung and causing pleuritic pain.

Risk factors for pulmonary embolism are divided into major and minor factors. This is important for pre-test clinical probability scoring (box 1). Recent studies in hospital in-patients with a wide variety of acute medical illnesses have shown a risk of venous thromboembolism comparable with that seen after major general surgery.5

“Economy class syndrome”

“Economy class syndrome” is thromboembolic disease associated with long distance sedentary travel; the incidence of venous thromboembolic disease increases with distance travelled. The importance of this causal link is under debate as most travellers who develop venous thromboembolism have additional risk factors.8 A 2001 study of 135.29 million passengers showed an incidence of pulmonary embolism of 1.5 cases per million for travel over 5000 km, compared with 0.01 cases per …

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