Pulmonary Embolism

A pulmonary embolism is the sudden blocking of one of the arteries of the lung by matter in the blood, such as a blood clot, fat, fragments of a cancerous tumor or an air bubble. The blockage prevents enough oxygen-rich blood from reaching the tissues of the lung, causing lung tissue to die (pulmonary infarction). Smaller clots are sometimes broken up by the body, so damage is minimal. If the clot is large, it can strain the heart or even cause death.


Symptoms depend on how completely the pulmonary artery is blocked and on the person's overall health. Symptoms are more serious if the person also has a serious disease, such as chronic obstructive pulmonary disease or coronary artery disease.

Some symptoms may include: 

  • Light-headedness, fainting or seizures because not enough oxygen-rich blood is getting to the brain and other organs
  • Irregular heartbeats
  • Bluish skin (cyanosis)
  • Sudden death

The symptoms of pulmonary embolism usually develop suddenly. By contrast, signs of pulmonary infarction (tissue death) develop slowly over several hours after the pulmonary embolism occurred. Pulmonary infarction may cause coughing that produces bloodstained sputum, sharp chest pain when breathing in and sometimes a fever. These symptoms often last several days, growing milder with each passing day.


Causes and Risk Factors

An embolism may be any of a variety of things, including:

  • A blood clot is the most common type of embolus that blocks the lungs. It usually forms in a leg or pelvic vein when a person has remained in one position for a long time. Examples include being on bed rest for a long period of time or sitting in one position while traveling by air. Once a person begins moving again, the clot can break loose. Sometimes - but more rarely - blood clots form in the veins of the arms or in the right side of the heart.
  • Fat, which can escape from the bone marrow when a bone is fractured. This is relatively rare.
  • Amniotic fluid, which may be forced into the pelvic veins during childbirth. This also is relatively rare.
  • Cancerous tumor fragments, which may break free into the blood stream
  • Air bubbles, which can not only block blood flow if they are large but also prevent the heart from effectively pumping blood. The air bubble may be introduced during intravenous delivery of drugs, nutrients or fluids. An air bubble embolism may also form when a vein is operated on or when a person is being resuscitated because of the force of having pressure put on their chest. Underwater diving can cause an air embolism; the risk depends on how deeply the person dives and how fast he or she returns to the surface of the water.

A person is at greater risk of developing blood clots in the veins if any of the following factors are present:

  • Advanced age
  • Blood clotting disorder
  • Cancer
  • Heart attack or failure
  • Irregular heartbeat (atrial fibrillation)
  • Major surgery
  • Obesity
  • Paralysis
  • Pelvis, hip, or leg fracture
  • Prior blood clot
  • Prolonged bed rest or sitting during a long car or plane trip
  • Stroke
  • Use of oral contraceptives, especially by a smoker after age 35


To diagnose a pulmonary embolism, a physician performs a physical examination and takes note of the patient's symptoms, risk factors or recent events (such as surgery, bed rest or travel) in his or her life that might lead to a blood clot. A large pulmonary embolism may be easy for a doctor to diagnose, especially when there are signs of a blood clot in a leg. Many emboli can be subtle and difficult to diagnose with certainty.

Some tests or procedures that a doctor may order to confirm a diagnosis include a(n):

  • Chest X-ray, which may show changes in blood vessel patterns or signs of lung tissue infarction
  • Electrocardiogram, which may show abnormalities
  • Lung perfusion scan, which is one of the best tests for diagnosing pulmonary embolism. For this test, a small amount of a radioactive substance is injected into a vein and travels to the lungs. Once there it shows where there is blood supply (perfusion) to the lung - and where there is not because of an embolism.
  • Lung ventilation scan, which is usually done with the perfusion scan. This test requires the patient to breathe in a harmless gas that contains a small amount of radioactive material. This material flows throughout the lung's small air sacs (alveoli). The areas where carbon dioxide is being released and oxygen taken up can then be seen on a scanner.

    By comparing this scan to the pattern of blood supply shown on the perfusion scan, a doctor can usually see whether a person has had a pulmonary embolism.
  • Pulmonary angiography, which can be more accurate in diagnosing a pulmonary embolism. It also is riskier and more uncomfortable than the other tests, so it is usually only done when the other tests cannot confirm the presence of a pulmonary embolism. In this test, a radioactive dye is injected into the pulmonary arteries. Using X-rays to follow the path of the dye, any blocked area from an embolism will block the dye.
  • Computed tomography (CT) is an accurate diagnostic procedure that can be used if pulmonary angiography is not available or the patient can't have angiography for some reason.
  • Blood tests
  • Ultrasound of the legs, which may show blood clots in the veins where the clot originated from


Because a pulmonary embolism can be life threatening and treatment is limited, precautions should be taken to prevent blood clots in persons who are at high risk of developing a pulmonary embolism. Preventive measures include:

  • Be active and move around every two hours, especially when traveling by air
  • After surgery - especially older people - should wear compression elastic stockings, do leg exercises and get out of bed and become active as soon as possible. If this isn't possible, devices that provide a rhythmic pressure on the legs can help keep blood moving. These devices alone may not be adequate.
  • Taking drugs, such as heparin or warfarin, to prevent the blood from clotting, especially before surgery

Without treatment, about half the people who have one pulmonary embolism will have another. About half the people who have a second pulmonary embolism may die. Treatment of a pulmonary embolism may include the following:

  • Oxygen
  • Pain relievers
  • Administering heparin or warfarin to prevent clots from forming or getting larger. Drugs to prevent the blood from clotting may be given for two months up to indefinitely depending on the person's health and risk factors for developing more pulmonary emboli
  • Drugs to break up and dissolve clots such as streptokinase or tissue plasminogen may be given. These drugs cannot be given to someone who has had surgery within the past two weeks, is pregnant, has had a stroke or tends to bleed too much.
  • Surgery may be needed in severe cases where the embolism is life threatening and must be removed.
  • Surgery to implant a filter in the main vein in the abdomen that drains blood from the legs and pelvis to the right side of the heart. This is done when emboli develop in spite of drugs to prevent clotting or if a person is not able to take those drugs. The filter prevents clots that may develop from being carried into the lungs.
  • Oxygen therapy and use of a ventilator may be needed for emboli that form from fat or amniotic fluid.