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A pulmonary embolus is a blockage of an artery in the lungs by fat, air, a blood clot, or tumor cells.

Venous thromboembolism; Lung blood clot; Blood clot - lung; Embolus; Tumor embolus

A pulmonary embolus is most often caused by a blood clot in a vein, especially a vein in the leg or in the pelvis (hip area). The most common cause is a blood clot in one of the deep veins of the legs. This type of clot is called a deep vein thrombosis (DVT).

Less common causes include air bubbles, fat droplets, amniotic fluid, or clumps of parasites or tumor cells, all of which may lead to a pulmonary embolus.

Risk factors for a pulmonary embolus include:

• Burns
• Cancer
• Childbirth
• Family history of blood clots
• Fractures of the hips or femur
• Heart attack
• Heart surgery
• Long-term bed rest or staying in one position for a long time, such as a long plane or car ride
• Severe injury
• Stroke
• Surgery (especially orthopedic or neurological surgery)
• Use of birth control pills or estrogen therapy

People with certain clotting disorders may also have a higher risk.

• Chest pain
  • Under the breastbone or on one side
  • Especially sharp or stabbing; also may be a burning, aching, or dull, heavy sensation
  • May get worse with deep breathing, coughing, eating, bending, or stooping (person may bend over or hold his or her chest in response to the pain)
• Cough
  • Begins suddenly
  • May cough up blood or blood-streaked sputum
• Rapid breathing
• Rapid heart rate
• Shortness of breath
  • May occur at rest or during activity
  • Starts suddenly

Other symptoms that may occur:

• Anxiety
• Bluish skin discoloration
• Clammy skin
• Dizziness
• Leg pain in one or both legs
• Lightheadedness or fainting
• Low blood pressure
• Lump associated with a vein near the surface of the body, may be painful
• Nasal flaring
• Pelvis pain
• Sweating
• Swelling in the legs
• Weak or absent pulse
• Wheezing

The following lab tests may be done to see how well your lungs are working:

• Arterial blood gases
• Pulse oximetry

The following imaging tests can help determine where the blood clot is located:

• Chest x-ray
• CT angiogram of the chest
• Pulmonary ventilation/perfusion scan
• Pulmonary angiogram

Other tests that may be done include:

• Chest CT scan
• Chest MRI scan
• D-dimer level
• Doppler ultrasound exam of an extremity
• ECG
• Echocardiogram
• Plethysmography of the legs
• Venography of the legs

It is difficult to predict how well a patient will do. Often, the outlook is related to what put the person at risk for pulmonary embolism (for example, cancer, major surgery, trauma). In cases of severe pulmonary embolism, where shock and heart failure occur, the death rate may be greater than 50%.

• Heart failure or shock
• Heart palpitations
• Pulmonary hypertension
• Severe breathing difficulty
• Severe bleeding (usually a complication of treatment)
• Sudden death

Go to the emergency room or call the local emergency number (such as 911) if you have symptoms of pulmonary embolus.

Preventing deep venous thrombosis (DVT) is very important, especially in people at high risk. To help prevent DVT, move your legs often or take a stroll during long plane trips, car trips, and other situations in which you are sitting or lying down for long periods of time. Walking and staying active as soon as possible after surgery or during a long-term medical illness can also reduce your risk.

Heparin therapy (low doses of heparin injected under the skin) may be prescribed for those on prolonged bedrest.

Sometimes patients in the hospital wear special soft boots that automatically (and gently) squeeze the calves periodically. This is called intermittent pneumatic compression. It helps keep blood moving and prevents blood clotting.

Anderson DR, Kahn SR, Rodger MA, et al. Computed tomographic pulmonary angiography vs ventilation-perfusion lung scanning in patients with suspected pulmonary embolism: a randomized controlled trial.JAMA. 2007;298(23):2743-53.

Righini M, Le Gal G, Aujesky D, et al. Diagnosis of pulmonary embolism by multidetector CT alone or combined with venous ultrasonography of the leg: a randomised non-inferiority trial. Lancet. 2008;371(9621):1343-52.

Snow V, Qaseem A, Barry P, et al. Management of venous thromboembolism: a clinical practice guideline from the American College of Physicians and the American Academy of Family Physicians. Ann Intern Med. 2007;146(3):204-10. Epub 2007 Jan 29.

Tapson VF. Pulmonary embolism. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007: chap 99.