Pulmonary thromboembolism Dr Trisha Macnair Pulmonary thromboembolism is a blockage of one of the arteries in the lung by a blood clot. The symptoms can be so vague it may be confused with many other conditions, and is frequently fatal.

In this article

What causes it? What are the symptoms?

Who's affected? How is it diagnosed?

What's the treatment? Can it be prevented?

Microscopic thrombi, or clots, are continually being made in the bloodstream. Normally, these are broken down quickly, but under certain conditions they grow to form a larger clot that blocks a vein. This is called deep vein thrombosis (DVT).

Conditions that trigger a thrombosis include:

• Slow or turbulent flow of blood through the veins (venostasis)
• Abnormality of the clotting system of the blood, which makes it more prone to forming clots or less able to break them down
• Inflammation of the blood vessel wall

DVTs usually form in the veins of the lower leg or pelvis, but can start anywhere in the body. Pieces may break loose and travel through the bloodstream to the lung, where they block the pulmonary blood vessels and stop blood travelling through the lung to collect oxygen. This is a pulmonary embolism (PE), the result of which is dangerously low levels of oxygen in the blood and tissues.

It can be difficult to spot a thrombosis. DVT in the calf veins, for example, has usually spread above the knee before a diagnosis is made.

While tests show that almost everyone who develops DVT in the upper leg has a PE, only about half have symptoms.

Symptoms of a pulmonary embolism may come on suddenly and include shortness of breath, chest pain, coughing up blood, low blood pressure and a painful, swollen red leg (indicating DVT).

It's estimated pulmonary embolisms are responsible for ten per cent of all deaths in hospital and play a part in a further ten per cent of deaths.

The condition is particularly common among the seriously ill or immobilised. More than ten per cent of people who rest in bed for a week develop PE, while 33 per cent of those in intensive care do so.

There are a number of factors that are known to increase a person's risk of PE. These include:

• Having an operation, especially orthopaedic surgery on the legs or gynaecological surgery
• Major trauma
• Serious burns
• Cancer
• Immobility, including prolonged periods of sitting still (during travel, for example)
• Pregnancy
• Paralysis
• Heart failure
• Inflammatory bowel disease
• Clotting disorders and thrombophilia

Tests to confirm a pulmonary thromboembolism include a lung scan called a ventilation-perfusion or V/Q scan (isotope lung scan), a pulmonary angiogram, electrocardiogram (ECG), ultrasound scan, CT or MRI scans, and another type of test called a D-dimer test.

Treatment of pulmonary thromboembolism must be prompt: ten per cent of patients die within the first hour.

The specific treatment depends on the likelihood that an embolism has occurred, the severity of symptoms and whether there's existing heart or lung disease.

Anticoagulant drugs such as heparin are used to stop clots in the lung growing any larger, allowing the body to break them down, and to prevent new clots forming. Such drugs don't dissolve the existing clot, but they do reduce the threat of another PE developing. It may be necessary to take these drugs for several months.

Large embolisms may be treated with drugs called thrombolytics, which dissolve the clot, or may require surgery.

There are ways of cutting down your risk of developing DVT or PE:

• Stop or cut down smoking
• Avoid being overweight t
• Avoid taking the contraceptive pill, particularly certain types, and hormone replacement therapy (HRT)
• Take regular exercise
• When travelling, exercise at regular intervals, keep well hydrated and wear compression stockings

This article was last medically reviewed by Dr Rob Hicks in July 2006.