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Pulmonary Embolism

As the heart pumps blood into the lungs to be oxygenated, a blood clot carried in the bloodstream may lodge in a pulmonary artery.

What is it?

A pulmonary embolism is a blood clot that travels through the veins to block a pulmonary artery, one of the vessels that carry blood to the lungs to be oxygenated. In most cases the blood clot (thrombus) originates in a leg vein, owing to a condition known as deep-vein thrombosis; the next most common sources are the right chambers of the heart. Part or all of a loosened thrombus may be carried into the pulmonary arteries. (Clumps of cancerous cells, fat, or bubbles of air in the bloodstream may also form emboli, although this is rare.) An embolus lodges in the main pulmonary artery or one of the smaller ones, cutting off the blood flow through the affected portion of the lungs. Symptoms occur suddenly; severity depends on the size and number of emboli. The disorder may quickly turn fatal if a large enough portion of the lungs is affected by either one large embolus or many smaller ones. Approximately one case in 10 results in sudden death. The first hour of a pulmonary embolism is crucial, so emergency treatment should be sought immediately; patients who survive long enough to be hospitalized and diagnosed usually recover. In the United States over a half million cases of pulmonary embolism occur each year.Outlook is most favorable among younger patients. Pulmonary embolism affects significantly more women than men (in an approximately two-to-one ratio).

What Causes It?

  • A blood clot dislodged from a leg vein is the most common cause of pulmonary embolism.
  • Rarely, an air bubble or a clump of cancerous cells, fat, bacteria, or other material may lodge in a pulmonary artery.
  • Risk factors include pregnancy; recent surgery; previous heart attack or stroke; prolonged bed rest (for example, while recovering from an illness); obesity; smoking; bone fractures, especially of the hip or leg bones; cancer, especially of the lungs, brain, breast, or liver; and family history of venous thrombosis, pulmonary embolism, or certain blood clotting disorders.
  • People with heart disease, emphysema, or chronic bronchitis are at greater risk of severe consequences from pulmonary embolism (see Coronary Artery Disease or Chronic Obstructive Pulmonary Disease for more information).

Prevention

  • Prescription elastic support hose may be worn to prevent deep-vein thrombosis in the legs among those at risk. Try not to cross the legs when sitting, as this promotes thrombus development.
  • Regular doses of aspirin may be prescribed to prevent the development of blood clots for those at high risk.
  • Heparin, an anticoagulant, may be administered in low, continuous doses to decrease the possibility of blood clots in people at risk (for example, those with chronic venous insufficiency, congestive heart failure, or in those who have recently had a heart attack) or in people about to undergo surgery. After surgery, such patients are encouraged to get up and walk as soon as possible to improve circulation.
  • Another form of heparin, low-molecular weight heparin, may be an alternative to heparin. It can be taken intermittently.
  • Coumadin, another anticoagulant, may be prescribed on a chronic basis once the acute symptoms of the embolism have resolved.

Diagnosis

  • Patient history and physical examination.
  • Chest x-ray.
  • An electrocardiogram (ECG) is performed to rule out a heart attack and to detect evidence of increased pressure in the pulmonary arteries or of other serious cardiovascular conditions.
  • Radionuclide scanning, which involves inhaling a small amount of radioactive gas and injection of radioactive particles into the bloodstream, may highlight blocked portions of the blood vessels in the lungs on an x-ray scan.
  • Pulmonary arteriography (injection of a contrast dye into the pulmonary arteries prior to taking a series of x-rays) is the only certain way to identify pulmonary embolism.
  • Contrast CT (computed tomography) scans are used to look for large pulmonary emboli.

How to Treat It

  • Anticoagulant drugs, like heparin and warfarin, are administered to prevent further blood clots.
  • Thrombolytic (clot dissolving) medications such as tPA (tissue plasminogen activator), streptokinase, or urokinase may be injected into the bloodstream to clear the blockage.
  • Analgesics are given to relieve pain.
  • Oxygen may be administered via an oxygen mask or, in severe cases, a respirator.
  • Emergency treatment is necessary for a suspected pulmonary embolism. Immediate surgical removal may be required when a large embolus is blocking a major pulmonary artery.

When to Call a Doctor

  • EMERGENCY Call an ambulance immediately if you or someone in your presence develops sudden, severe chest pain and shortness of breath, along with feelings of great apprehension or dread. In addition to pulmonary embolism, such symptoms may also be indications of a heart attack or other serious cardiovascular crisis.
  • EMERGENCY Call an ambulance immediately any time someone unexpectedly loses consciousness.