Pulmonary Embolism

What is pulmonary embolism?

Pulmonary embolism is the sudden blockage of an artery in the lung. Once the artery is blocked, usually by one or more blood clots, oxygen levels in the blood drop, and blood pressure in the lungs rises.

Pulmonary embolism caused by large clots can cause sudden death, usually within 30 minutes of when symptoms begin.¹ Smaller clots may cause permanent damage to the heart and lungs.

What causes pulmonary embolism?

The most common cause of pulmonary embolism is a blood clot that forms in a deep vein in your leg, breaks loose, travels to the lungs, and becomes trapped in one of the smaller lung arteries. Other substances, such as tumors, air bubbles, amniotic fluid, or fat that is released into the blood vessels, may also block an artery, but such causes are rare.

What are the symptoms?

Shortness of breath is the most common symptom of pulmonary embolism. You may have sharp chest pain, which can spread to your shoulder, neck, jaw, or arm. You may also have a cough that produces a pink, foamy mucus. Other symptoms may include anxiety, sweating, lightheadedness, fainting, rapid heart rate or palpitations, and an impending sense of doom. Symptoms of pulmonary embolism often begin suddenly.

What increases your risk of pulmonary embolism?

A blood clot in the deep leg veins (deep vein thrombosis) is the greatest risk factor for pulmonary embolism. Inactivity, especially long periods of bed rest, long flights, or car trips, increases your risk of pulmonary embolism because of reduced blood circulation. Recent surgery, stroke, heart attack, heart failure, cancer, lung disease, being overweight, using birth control pills, and smoking are also risk factors for pulmonary embolism.

Some people have blood that clots too quickly, and they are more likely to develop clots that cause deep vein thrombosis or pulmonary embolism. Conditions that cause increased clotting include inherited factors, cancer, and severe infections. Injury to a blood vessel also increases the risk of deep vein thrombosis.

How is pulmonary embolism diagnosed?

Many different types of tests, such as a chest X-ray, spiral CT scan, lung scan, or ultrasound, can be used to diagnose pulmonary embolism. However, it can be difficult to diagnose because other conditions, such as a heart attack, panic attack, or pneumonia, can cause similar symptoms.

Your doctor will consider your symptoms and risk factors for pulmonary embolism before deciding which tests you should have first. If you are at risk for pulmonary embolism and have symptoms, you should seek emergency care immediately. Some people with this condition, however, have no symptoms.

How is it treated?

Treatment focuses on preventing another clot from developing and preventing existing clots from growing. Heparin and warfarin are anticoagulant medications that are most commonly given to prevent the growth of existing blood clots or the development of new blood clots. Blood clots that cause pulmonary embolism often will dissolve on their own in a few weeks or months, although they may never dissolve completely.

In rare cases, other treatments for pulmonary embolism may be considered. Clot-dissolving drugs (thrombolytics) may be used, or a surgeon may remove the clot in a procedure called an embolectomy. To prevent future pulmonary embolism, a filter may be placed inside the large central vein (vena cava) of the body to trap clots and prevent them from traveling to the lungs.

See an illustration of a clot that may lead to pulmonary embolism.

Frequently Asked Questions

Pulmonary embolism is caused by a blocked artery in the lungs. The most common cause of such a blockage is a blood clot that forms in a deep vein in the leg and travels to the lungs, where it becomes lodged in a smaller lung artery.

Over 95% of blood clots that cause pulmonary embolism are formed in the upper deep leg veins.² Clots can also form in the lower deep veins of the legs as well as the deep veins of the arms or pelvis. However, only about 20% of blood clots in the veins of the calf will become larger and move into the upper leg or groin veins.³

Occasionally blood clots develop in surface veins, but these clots rarely lead to pulmonary embolism.

In rare cases, pulmonary embolism may be caused by other substances, including:⁴

• Tumors caused by rapidly growing cancer cells.
• Air bubbles from trauma, surgery, or medical procedures.
• Amniotic fluid from normal or complicated pregnancy and childbirth (very rare).
• Small masses of infectious material.
• Fat, which can be released into the bloodstream after some types of bone fractures, surgery, trauma, or severe burns or from diseases.
• Foreign substances, such as a catheter needle that can break off during a medical procedure, mercury, iodine, cotton, or the growth of tapeworm larvae.

The symptoms of pulmonary embolism may include:

• Shortness of breath that may occur suddenly.
• Sudden, sharp chest pain that may become worse with deep breathing or coughing.
• Rapid heart rate.
• Rapid breathing.
• Sweating.
• Anxiety.
• Coughing up blood.
• Fainting.
• Heart palpitations.
• Signs of shock.

Pulmonary embolism may be difficult to diagnose because its symptoms may occur with or are similar to other conditions, such as a heart attack, a panic attack, or pneumonia. Also, some people with pulmonary embolism do not have symptoms.

See a list of other conditions with similar symptoms.

If a large blood clot blocks the artery in the lung, blood flow may be completely stopped, causing sudden death. A smaller clot reduces the blood flow and may cause damage to lung tissue. However, if the clot dissolves on its own, it may not cause any major problems.

Symptoms of pulmonary embolism usually begin suddenly. Reduced blood flow to one or both lungs can cause shortness of breath and a rapid heart rate. Lowered oxygen levels may also cause sharp chest pain and damage to lung tissue.

Pulmonary embolism is likely to recur without treatment.

Complications of pulmonary embolism

Complications of pulmonary embolism may include:

• Cardiac arrest and sudden death.
• Shock.
• Abnormal heart rhythms.
• Death of part of the lung, called pulmonary infarction.
• A buildup of fluid (pleural effusion) between the outside lining of the lungs and the inner lining of the chest cavity.
• Paradoxical embolism.
• Stroke.
• Heart attack.

Aggressive steps will be considered when treating a large, life-threatening pulmonary embolism. Death caused by pulmonary embolism usually occurs within 30 minutes of the onset of symptoms.¹

Chronic or recurring pulmonary embolism

Blood clots that cause pulmonary embolism may dissolve on their own. However, after having had pulmonary embolism, you have an increased risk of a repeat episode if you do not receive treatment. If pulmonary embolism is diagnosed promptly, treatment with anticoagulant medications (usually heparin and warfarin) may prevent new blood clots from forming.

The risk of having another pulmonary embolism caused by something other than blood clots varies. Substances that are reabsorbed into the body, such as air, fat, or amniotic fluid, usually do not increase the risk of having another episode. Cancer increases the risk of blood clots.

Having multiple episodes of pulmonary embolism can severely reduce blood flow through the lungs and heart. Over time, this increases blood pressure in the lungs (pulmonary hypertension), eventually leading to right-sided heart failure and possibly death.

Having a blood clot in the deep vein of your leg and having a previous pulmonary embolism are the two greatest risk factors for pulmonary embolism.

For more information on risk factors for blood clots in the legs, see the topic Deep Vein Thrombosis.

Risk factors for developing clots include having slowed blood flow, abnormal clotting, and a blood vessel injury.

Slowed blood flow

When blood does not circulate normally, clots are more likely to develop. Reduced circulation may result from:

• Long-term bed rest, such as if you are confined to bed after an operation, injury, or serious illness.
• Traveling and sitting for a long time, especially when traveling long distances by airplane.⁵
• Leg paralysis. Paralysis can reduce circulation because the legs cannot be moved without help.

Abnormal clotting

Some people have blood that clots too easily or too quickly. People with this problem are more likely to form larger clots that can break loose and travel to the lungs. Conditions that may cause increased clotting include:

• Inherited factors. Some people have an inherited tendency to develop blood clots that can lead to pulmonary embolism.
• Cancer.
• Heart failure.
• Serious burns.
• Severe infections.
• Use of birth control pills or other medications that contain estrogen or estrogenlike hormones.⁶
• Smoking.

Injury to the blood vessel wall

Blood is more likely to clot in veins and arteries shortly after they are injured. Injury to a vein can be caused by:

• Major surgery involving the legs, abdomen, or pelvis.
• A tube (catheter) placed in a large vein of the body (central venous catheter).

Other risk factors include:

• Pregnancy. A woman's risk of developing blood clots increases both during pregnancy and shortly after delivery.
• Age. As people get older (especially older than age 70), they are more likely to develop blood clots.
• Weight. Being overweight increases the risk for developing clots.
• Not taking anticoagulant medication as prescribed.

Call 911 or other emergency services immediately if you think you have symptoms of pulmonary embolism. Symptoms include:

• Sudden shortness of breath.
• Sharp chest pain that sometimes becomes worse with deep breathing or coughing.
• Rapid pulse or palpitations.
• Sweating.
• Anxiety.
• A cough that may produce a bloody mucus or blood.
• Fainting.

Call your doctor right away if you have symptoms of a blood clot in the leg. These symptoms may include:

• Swelling in a leg that may make it noticeably larger than the other leg. Swelling may also appear as a swollen ridge along a blood vessel that you can feel.
• Skin that is red and warm to the touch.
• Pain or tenderness in the calf or thigh. The pain may occur only when standing or walking.

Blood clots in the deep veins of the leg are the most common cause of pulmonary embolism. For more information on these types of blood clots, see the topic Deep Vein Thrombosis.

Watchful Waiting

If you think you may have pulmonary embolism, call your doctor or go to the emergency room at the nearest hospital. Watchful waiting is not appropriate for pulmonary embolism.

Who To See

Health professionals who can diagnose pulmonary embolism include:

• An emergency room doctor.
• An internal medicine doctor (internist).
• A family medicine doctor.
• A nurse practitioner or physician assistant.
• A pulmonologist.
• A cardiologist.
• A surgeon. This is most often a general surgeon, an orthopedic (bone) surgeon, or a vascular (vein) surgeon.
• An obstetrician (if pulmonary embolism is pregnancy-related).

To prepare for your appointment, see the topic Making the Most of Your Appointment.

Diagnosing pulmonary embolism is difficult because of the large number of other medical conditions that can cause similar symptoms, such as a heart attack or an anxiety attack.

Diagnosis depends upon an accurate and thorough medical history and ruling out other conditions. Your doctor will need to know about your symptoms and risk factors for pulmonary embolism, such as having a prior or family history of blood clots or having recent surgery. This information, combined with a careful physical exam, will guide which initial tests are best suited to diagnose a deep vein thrombosis or pulmonary embolism.

Tests that are often done if you have shortness of breath or chest pain include:

• A chest X-ray. Results may rule out an enlarged heart or injured lung, which may lead to further testing.
• Electrocardiogram (EKG, ECG). The electrical activity of the heart is recorded with this test. EKG results will help rule out a possible heart attack.
• Arterial blood gas analysis. A sudden drop in the blood oxygen level may suggest a pulmonary embolism.

Results from these initial tests may rule out other conditions, such as a heart attack or pneumonia. Further testing may include:²

• D-dimer. A d-dimer test is a blood test that measures a substance released as a blood clot breaks up. D-dimer levels are usually high in people with pulmonary embolism.
• Spiral (helical) computed tomography. This test is used commonly in most hospitals to check for pulmonary embolism.
• Ventilation-perfusion scanning. This test scans for abnormal blood flow through the lungs after a radioactive tracer has been injected and you breathe a radioactive gas.
• Pulmonary angiogram. A pulmonary angiogram is the most accurate way to diagnose pulmonary embolism. This test is not available at some smaller hospitals and is more invasive than other testing.
• Echocardiogram (echo). This test detects abnormalities in the size or function of the heart's right ventricle, which may be an indicator of pulmonary embolism.
• Doppler ultrasound. A Doppler ultrasound test uses reflected sound waves to determine whether a blood clot is present in the large veins of the legs.
• Magnetic resonance imaging (MRI). This test may be used to view clots in the deep veins and lungs.

Treatment of pulmonary embolism focuses on preventing future pulmonary embolism by using anticoagulant medications. Anticoagulants prevent existing blood clots from growing larger and help prevent new ones from developing.

If symptoms are severe and life-threatening, immediate and sometimes aggressive treatment is needed. Aggressive treatment may include thrombolytic medications, which can dissolve a blood clot quickly but also increase the risk of severe bleeding. Another option for life-threatening, large pulmonary embolism is surgical removal of the clot, called an embolectomy. This surgery is only available at a few large hospitals.

Some people may also benefit from having a vena cava filter inserted into the large central vein of the body. This filter can help prevent blood clots from reaching the lungs. It is used when anticoagulants are not an option, clots form despite anticoagulant use, or there is an increased risk of death or a severely restricted lifestyle if another pulmonary embolism occurs.

Daily use of anticoagulant medicines may help prevent recurring pulmonary embolism by stopping new blood clots from forming and stopping existing clots from growing.

Recent studies show that the risk of forming another blood clot is highest during the 4 to 6 weeks after an initial episode of pulmonary embolism. This risk decreases over time. However, the risk remains significant for months and sometimes years depending upon what caused the pulmonary embolism. People with recurrent blood clots and/or pulmonary embolism may have to take anticoagulants daily for the rest of their lives.⁷ Anticoagulant medications also are often used for people who are having surgery on the legs, abdomen, or pelvis.

Other preventive methods may also be used, such as:

• Getting you moving shortly after surgery.
• Wearing compression stockings to help prevent leg deep vein thrombosis if you are at increased risk for this condition.
• Taking a baby aspirin before long airplane or car trips.

Aspirin may reduce the risk of forming blood clots.⁸ Aspirin, however, is not adequate for treating pulmonary embolism.

Home treatment is not recommended for initial treatment for pulmonary embolism. However, it is important for preventing additional clots from developing and causing a deep vein thrombosis, which can lead to recurring pulmonary embolism.

Measures that decrease your risk of developing a deep vein thrombosis include the following:

• Exercise. Keep blood moving in your legs by pointing your toes up toward your head so that your calves are stretched, then relaxing. Repeat. This exercise is especially important when you are sitting for long periods of time, for example, on long driving trips or airplane flights.
• Get up out of bed as soon as possible after an illness or surgery. It is very important to get moving as soon as you are able. If you cannot get out of bed, do the leg exercises described above every hour to keep the blood moving through your legs.
• Quit smoking. This is especially important if you are using any medications that contain estrogen, such as birth control pills.
• Wear compression stockings to help prevent leg deep vein thrombosis if you are at increased risk for this condition.

For more information on how to prevent clots from developing, see the topic Deep Vein Thrombosis.

Medications can help prevent repeated episodes of pulmonary embolism by preventing new blood clots from forming or preventing existing clots from getting larger.

Medication Choices

Anticoagulants are prescribed when pulmonary embolism is diagnosed or strongly suspected. Normally, when an injury that causes bleeding occurs, the body sends out signals that cause the blood to clot at the wound. The clot naturally breaks down as the wound heals. A person who is prone to abnormal clotting has an imbalance between clot formation and clot breakdown. Anticoagulants prevent the production of certain proteins that are necessary for blood to clot. Although anticoagulants can prevent new clots from forming and prevent existing clots from getting larger, they do not break up or dissolve existing blood clots.

Heparin and warfarin are the two main types of anticoagulants used to treat pulmonary embolism.

Heparin

Heparin is an anticoagulant given by injection. It immediately affects the clotting system in your body. Oral anticoagulant medication (warfarin) takes longer to start working.

• Initial treatment with a low-molecular-weight heparin (LMWH) usually is preferred because it can be given as an injection once or twice per day, and it may be given at home, allowing you to leave the hospital earlier.⁹ Blood tests are not needed to monitor LMWH's clotting effect.
• Unfractionated heparin is another form that can be used. It is given in the hospital continuously through your vein (intravenously, or IV). Frequent blood tests (usually every 6 hours) are required to monitor the clotting effects of this medication.

Early studies show that LMWH may be equally as effective as unfractionated heparin in most people with pulmonary embolism.^{10, 11} However, it is still unclear whether LMWH is a good choice in treating a large pulmonary embolism. Some doctors may still prefer to use unfractionated heparin in these severe cases.

Both forms of heparin can cause severe bleeding in some people. The risk that either type will cause bleeding appears to be about the same.² However, if bleeding occurs, unfractionated heparin can be stopped quickly, whereas LMWH has to wear off.

Warfarin (such as Coumadin)

Warfarin is an anticoagulant that is taken in pill form. It is usually started while a person is still being treated with heparin because it takes several days for warfarin to build up to a level that's effective. Once the warfarin is at a proper level, heparin is discontinued and treatment with warfarin continues. Studies show that treatment using heparin and warfarin reduces the risk of death from pulmonary embolism.¹¹

Typically, full-dose warfarin is given for at least 3 to 6 months or longer after pulmonary embolism to reduce the risk of having another blood clot. Treatment with anticoagulants may continue throughout your life if the risk of having another pulmonary embolism remains high. Talk with your doctor about whether continuing low-dose warfarin after your initial treatment might be right for you.

For those people with ongoing risk factors, such as cancer, anticoagulant treatment continues as long as those risk factors are present. Some people with inherited blood-clotting disorders or a history of recurrent deep vein thrombosis or pulmonary embolism may take oral anticoagulants for the rest of their lives.

Because warfarin can increase the risk of birth defects, pregnant women with pulmonary embolism are limited to taking heparin. A few days after the baby is born, a woman can switch from heparin to warfarin.

Thrombolytics

Thrombolytic medications are not commonly used to treat pulmonary embolism. Although they can quickly dissolve a blood clot, thrombolytics also greatly increase the risk of serious bleeding. They are occasionally used to treat a life-threatening pulmonary embolism.

What To Think About

Once pulmonary embolism is diagnosed, a doctor considers:

• Whether anticoagulant medications are appropriate.
• How long anticoagulants should be used.

If you have had a recent major stroke, surgery, or active internal bleeding, you usually cannot take anticoagulant or thrombolytic medications. A vena cava filter may help to reduce the risk of another pulmonary embolism in this case.

It's important that you keep the following safety tips in mind when taking warfarin.

Safety tips for anticoagulants

• Take the medication at the same time each day.
• Check with your doctor before using nonprescription drugs, especially ones that contain aspirin.
• Tell any new health professionals that you are taking medication that affects how your blood clots.
• Be alert for signs of bleeding, and call the doctor immediately if any of the following symptoms occur:
  • Blood in urine or red or black tarry stools
  • Nosebleeds that are hard to stop
  • Spitting up blood
  • New, excessive, or prolonged vaginal bleeding
  • Frequent, severe bruising or tiny red or purple spots on the skin
• Talk to your doctor about medications you are taking to find out how often you should have blood tests.

If you are taking the anticoagulant ticlopidine, get frequent blood tests to check your white blood cell count during the first 3 months of treatment.

If you take warfarin (such as Coumadin):

• Get regular blood tests to ensure that you are taking the right amount of medication.
• Eat a balanced diet. Don't suddenly change your intake of vitamin K–rich foods, such as broccoli, brussels sprouts, cabbage, asparagus, lettuce, spinach, and some vegetable juices. It is most important to maintain a consistent level of vitamin K foods in your diet. Vitamin K can interfere with the action of warfarin, making it more likely that your blood will clot.
• Avoid excessive use of alcohol. If you drink, do so only in moderation. Chronic drinking may cause liver damage and increase the effect of warfarin.
• Don't use tobacco of any kind.
• Avoid activities that have a high risk for injury, such as skiing, football, or other contact sports. If you are taking warfarin, an injury could result in excessive bleeding.
• Wear a seat belt anytime you are traveling in a car.

Preventing minor bleeding while taking anticoagulants

You may find it helpful to use the following items to lower your risk of bleeding:

• An electric razor
• A soft-bristled toothbrush and waxed floss
• Protective clothing, such as gloves and shoes
• Nonslip mats in the tub and shower

Surgical removal of a clot is called an embolectomy. This type of treatment for pulmonary embolism is rarely used. It is considered when the clot in the main pulmonary artery is extremely large and life-threatening and is causing severe symptoms.⁷ An embolectomy also may be an option for a person whose condition is stable but who shows signs of significant reduced blood flow in the pulmonary artery.

What to Think About

Surgery increases the risk of forming new blood clots that can cause another pulmonary embolism.

Some people cannot take anticoagulant medications, or they continue to develop blood clots despite taking the medications. If surgery or medications are not options, other methods of preventing pulmonary embolism may be considered, such as a vena cava filter.

Other Treatment Choices

A vena cava filter may be inserted in the large central vein that passes through the abdomen and returns blood from the body to the heart (vena cava). This filter can prevent blood clots in the leg or pelvic veins from traveling to the lungs and heart. These filters may be permanent or removable.

Studies have shown that vena cava filters help prevent pulmonary embolism. However, they may be most effective when combined with anticoagulant therapy.

What To Think About

Vena cava filters are not recommended as an initial treatment for pulmonary embolism. However, they may be considered if you:

• Continue to have pulmonary embolism despite taking anticoagulant medication.
• Cannot take anticoagulants because of bleeding risk.
• Have an increased risk of death or a severely restricted lifestyle should another pulmonary embolism occur.

Vena cava filters may benefit people who have had a pulmonary embolism surgically removed (embolectomy) if another pulmonary embolism would likely be fatal or severely limit a person's lifestyle.

Vena cava filters can cause serious health problems if they become blocked with one or more blood clots.

Vena cava filters have not been shown so far to lower the death rate in people with pulmonary embolism.

Organizations

• Deep Vein Thrombosis

Citations

1. American College of Obstetricians and Gynecologists (2000). Prevention of deep vein thrombosis and pulmonary embolism. ACOG Practice Bulletin No. 21. Obstetrics and Gynecology, 96(4): 1–10.

2. Tapson V (2004). Pulmonary embolism. In L Goldman, D Ausiello, eds., Cecil Textbook of Medicine, 22nd ed., vol. 1, pp. 560–568. Philadelphia: Saunders.

3. Kearon C, Hirsh K (2003). Pulmonary embolism section of Venous thromboembolism. In DC Dale, DD Federman, eds., Scientific American Medicine, vol. 1 part 1, chap. 18. New York: WebMD.

4. Rossi SE, et al. (2000). Nonthrombotic pulmonary emboli. American Journal of Roentgenology, 174(6): 1499–1508.

5. Lapostolle F, et al. (2001). Severe pulmonary embolism associated with air travel. New England Journal of Medicine, 345(11): 779–783.

6. Grady D, et al. (2000). Postmenopausal hormone therapy increases risk for venous thromboembolic disease: The heart and estrogen/progestin replacement study. Annals of Internal Medicine, 132(9): 689–696.

7. Task Force on Pulmonary Embolism, European Society of Cardiology (2000). Task force report: Guidelines on diagnosis and management of acute pulmonary embolism. European Heart Journal, 21(16): 1301–1336.

8. Pulmonary Embolism Prevention (PEP) Trial Collaborative Group (2002). Prevention of pulmonary embolism and deep vein thrombosis with low-dose aspirin: Pulmonary embolism prevention (PEP) trial. Lancet, 355(9212): 1295–1302.

9. Hyers TM, et al. (2001). Antithrombotic therapy for venous thromboembolic disease. Sixth ACCP Consensus Conference on Antithrombotic Therapy. Chest, 119(1 Suppl): 176S–193S.

10. Hull RD, et al. (2000). Low-molecular-weight heparin versus heparin in the treatment of patients with pulmonary embolism. Archives of Internal Medicine, 160(2): 229–236.

11. Fitzmaurice D, et al. (2004). Thromboembolism. Clinical Evidence (11): 284–299.

Other Works Consulted

• Agency for Healthcare Research and Quality (2003). Diagnosis and Treatment of Deep Venous Thrombosis and Pulmonary Embolism. Evidence Report/Technology Assessment No. 68. (AHRQ Publication No.03–E012). Rockville, MD: Agency for Healthcare Research and Quality.

• Kearon CK, et al. (2003). Comparison of low-intensity warfarin therapy with conventional-intensity warfarin therapy for long-term prevention of recurrent venous thromboembolism. New England Journal of Medicine, 349(7): 631–639.

• Kucher N, Tapson VF (2004). Pulmonary embolism. In V Fuster et al., eds., Hurst's The Heart, 11th ed., pp. 1593–1616. New York: McGraw-Hill.

• Tapson VF (2002). Venous thromboembolism. In EJ Topol, ed., Textbook of Cardiovascular Medicine, 2nd ed., pp. 667–684. Philadelphia: Lippincott Williams and Wilkins.

Author:	Ellie Rodgers	Last Updated February 25, 2005
Medical Review:	Caroline S. Rhoads, MD - Internal Medicine Jeffrey S. Ginsberg, MD - Hematology
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