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

Pulmonary emboli are most often caused by blood clots in the veins, especially veins in the legs or in the pelvis (hips). More rarely, air bubbles, fat droplets, amniotic fluid, or clumps of parasites or tumor cells may obstruct the pulmonary vessels.

The most common cause of a pulmonary embolism is a blood clot in the veins of the legs, called a deep vein thrombosis (DVT). Many clear up on their own, though some may cause severe illness or even death.

Risk factors for a pulmonary embolus include:

• Prolonged bed rest or inactivity (including long trips in planes, cars, or trains)
• Oral contraceptive use
• Surgery (especially pelvic surgery)
• Childbirth
• Massive trauma
• Burns
• Cancer
• Stroke
• Heart attack
• Heart surgery
• Fractures of the hips or femur

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

Symptoms of pulmonary embolism may be vague, or they may resemble symptoms associated with other diseases. Symptoms can include:

• Cough
  • Begins suddenly
  • May produce bloody sputum (significant amounts of visible blood or lightly blood streaked sputum)
• Sudden onset of shortness of breath at rest or with exertion
• Splinting of ribs with breathing (bending over or holding the chest)
• Chest pain
  • Under the breastbone or on one side
  • Especially sharp or stabbing; also may be burning, aching or dull, heavy sensation
  • May be worsened by breathing deeply, coughing, eating, bending, or stooping
• Rapid breathing
• Rapid heart rate (tachycardia)

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

Tests to evaluate the function of the lungs:

• Arterial blood gases
• Pulse oximetry

Tests to detect the location and extent of embolism:

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

Tests to detect DVT:

• Doppler ultrasound exam of an extremity blood flow studies
• Venography of the legs
• Plethysmography of the legs

An ECG may show abnormalities caused by strain on the heart.

This disease may also alter the results of the following tests:

• Echocardiogram
• D-dimer level
• Chest CT scan
• Chest MRI scan

Emergency treatment and hospitalization may be necessary. In cases of severe, life-threatening pulmonary embolism, definitive treatment may consist of dissolving the clot with thrombolytic therapy. Anticoagulant therapy prevents the formation of more clots and allows the body to re-absorb the existing clots faster.

Clot-dissolving medication (thrombolytic therapy) includes streptokinase, urokinase, or t-PA. Clot-preventing medication (anticoagulation therapy) consists of heparin by intravenous infusion initially, then oral warfarin (Coumadin). Subcutaneous low-molecular weight heparin is substituted for intravenous heparin in many circumstances. Patients who have reactions to heparin or related medications may need other medications.

Patients who cannot tolerate anticoagulation therapy may need an inferior vena cava filter (IVC filter). This device, placed in the main central vein in the abdomen, is designed to block large clots from traveling into the pulmonary vessels. Oxygen therapy may be required to maintain normal oxygen concentrations.

Surgery is sometimes needed in patients at great risk for recurrent embolism.

It is difficult to predict how the patient will do in the future. Often, the outlook is related to the disease that puts 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 palpitations
• Heart failure or shock
• Severe breathing difficulty
• Sudden death
• Hemorrhage (usually a complication of thrombolytic or anticoagulation therapy)
• Pulmonary hypertension with recurrent pulmonary embolism

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

Prevention of deep venous thrombosis (DVT) among at-risk patients is very important. Walking and staying active as soon as possible after surgery or during a prolonged medical illness can reduce the risk for pulmonary embolus. Heparin therapy (low doses of heparin injected under the skin) may be used for those on prolonged bedrest. Other preventive measures include compression stockings (plastic sleeves that fit around the legs and help circulate the blood).

Perrier A, Roy PM, Aujesky D, et al. Diagnosing pulmonary embolism in outpatients with clinical assessment, D-Dimer measurement, venous ultrasound, and helical computed tomography: a multicenter management study. Am J Med. March 2004;116:291-299.

Ramzi DW, Leeper KV. DVT and Pulmonary Embolism: Part II. Treatment and Prevention. Am Fam Physician. June 15 2004;69:2841-2848.

Merli G. Diagnostic assessment of deep vein thrombosis and pulmonary embolism. Am J Med. August 2005;118:3S-12S.