Pulmonary Embolism

  • Definition

    Article updated and reviewed by Instructor, Division of Pulmonary, Critical Care & Sleep Medicine, Mount Sinai School of Medicine. Editorial review provided by VeriMed Healthcare Network on July 22, 2005.

    A pulmonary embolism is a blockage of a pulmonary artery (major blood vessel in the lung) by a fragment of material. Most commonly, a thrombus (blood clot) blocks the artery. In most cases, the blood clot forms elsewhere in the body, then breaks off and travels to the lung. In a small percentage of cases, the material may consist of air, fat, bone marrow, or amniotic fluid.


    blood clots generally form in leg veins when blood flows poorly in the thighs, calves, or ankles. This pooling causes platelets and other blood components to stick together and adhere to the wall of the vein. This pooling of blood leads to clot formation and thrombophlebitis (inflammation of the vein ).

    These blood clots are soft and prone to detach from the venous wall during injury, sudden muscle action, or a change in blood flow. When the clot blocks the pulmonary artery, the heart has more difficulty pumping blood through the lungs. The lungs respond to this blockage by releasing chemicals that may cause the blood vessels to spasm, causing further difficulty for the heart to pump blood. In addition, these chemicals may alter the pattern of air flow in the lungs. Together, these factors may result in labored breathing and chest pains.

    Pulmonary embolism may cause sudden death.


    Pulmonary embolism is diagnosed in about 500,000 persons each year in the United States, resulting in about 200,000 deaths.

    If untreated, pulmonary embolism causes death in about 30% of cases. If treated with anticoagulants (blood thinners), pulmonary embolism causes death in two to eight percent of cases.

    Physiological risk factors include venous stasis (poor blood flow in the veins), venous injury (injury to the veins), and having a condition or illness that predisposes to clotting (cancer, certain blood protein deficiencies, infection). Older persons seem to have a higher risk for pulmonary embolism, as do obese persons and women taking oral contraceptives. Some people have inherited abnormalities in blood clotting that make them more likely to have pulmonary embolism, as well as other clotting disorders, such as stroke and myocardial infarction (heart attack).

    Clinical risk factors include infection, prolonged bed rest or inactivity, recent surgery or childbirth, stroke, heart attack, congestive heart failure, obesity, and fractures of the pelvis (hip) or femur (leg bone).


    There may be no obvious warning signs and if there are symptoms, they often mimic those of other cardiopulmonary (heart-lung) disorders. The symptoms and signs may include:


    Pulmonary embolism can be extremely difficult to diagnose. Since many symptoms mirror other cardiopulmonary disorders, an accurate diagnosis may include a battery of tests with a thorough review of a person's medical history and physical examination. Doctors review a person's medical history for risk factors that would predispose them to pulmonary embolism.

    The risk factors include:

    After reviewing the person's medical history and performing a comprehensive physical exam, the doctors may perform a battery of diagnostic tests, including blood tests to evaluate clotting and evidence of pulmonary embolism.

    A chest x-ray helps evaluate whether there are other respiratory diseases.

    An electrocardiogram (EKG) monitors the heart's electrical activity and helps distinguish pulmonary embolism from other conditions. An echocardiogram (ultrasound of the heart) may be used in some cases: if strain on the right side of the heart appears, the suspicion of pulmonary embolism is higher.

    The arterial blood gas test measures the amount of oxygen in the blood that is being pumped from the heart to the rest of the body. People with a pulmonary embolus may have abnormally low oxygen levels.

    In a D-dimer test, blood is sampled to detect levels of molecules released from clot materials. When clots injure the blood vessels, D-dimer molecules are released into the bloodstream; these molecules, however, may be released in many other conditions, so a positive test does not necessarily mean that a person has a pulmonary embolism.

    A lung scan (V-Q scan) consists of an injection of radioactive tracer particles through an intravenous line. Normally, all parts of the lung light up from the radioactive tracer. In a pulmonary embolism, the area of the lung that is supplied by the blocked artery tends to have little or no detectable radioactivity.

    The identification of deep venous thrombosis (DVT; a clot in the vein) helps confirm the diagnosis of pulmonary embolism. An ultrasound study of the legs or a contrast venogram (injection of special dye visible on an x-ray into the leg veins) may be done to detect a blockage by a clot.

    A CT angiogram (a CAT-scan with a timed injection of a special dye visible on an x-ray) may also be used to evaluate a patient with a possible pulmonary embolism. If a pulmonary embolism is present, the dye will not flow completely through the lungs, and this lack of flow will be visible on the cat scan.

    A pulmonary angiogram is the “gold standard,” or most reliable test for a pulmonary embolism. In a pulmonary angiogram, a thin tube (catheter) is inserted into a vein and through the right side of the heart and into the pulmonary artery. A special dye visible on an x-ray is then injected into the vessel and the obstructive clots are detected.


    Treatment depends on the size and severity of the embolus. Current treatments include anticoagulant ('blood thinner') and oxygen therapy, thrombolysis, or a vena cava filter. If surgery is required, procedures include traditional pulmonary embolectomy or catheter-directed pulmonary embolectomy.

    Oxygen therapy

    If the pulmonary embolism results in a low blood oxygen level, oxygen will be administered either by nasal cannulae (small prongs that fit in the nostrils) or by face mask. In cases of severe pulmonary embolism, mechanical ventilation, (artificial respiration) may be necessary.

    Anticoagulant therapy

    Patients with stable acute pulmonary embolism are hospitalized immediately so that an anticoalgulant (blood thinning agent) can be given and oxygen can be administered (if needed). Anticoagulants permit quicker absorption of the clot, reducing the threat of another embolus.

    The most widely used intravenous anticoagulant is heparin is drug acts quickly and can stop blood-clot formation almost immediately. Treatment with heparin often requires frequent blood testing to ensure that the level of anticoagulation is neither too low nor too high. Other intravenous anticoagulant medications are available for those who have allergies to heparin.

    Several related medications known as “low molecular weight heparins” are available as subcutaneous (under the skin) injections, such as enoxaparin (Lovenox®), dalteparin (Fragmin®), or tinzaparin (Innohep®). When a person is receiving one of these medicines, blood testing does not need to be done so frequently. In some cases, a patient with a blood clot in the legs or a pulmonary embolism may be treated as an outpatient with a low molecular weight heparin.

    After a day or two of heparin or low molecular weight heparin, patients are often given warfarin (Coumadin® or Jantoven®), which is available as a pill. This medication acts more slowly and in a different way from heparin. Warfarin takes about three to five days to take effect so an injected drug is given until warfarin takes full effect.


    Thrombolysis, or reperfusion therapy, involves injecting a clot-dissolving medication into the circulation to dissolve the blood clot and restore blood flow. Unlike heparin, thrombolytic agents can dissolve an existing clot in both the deep venous system and the pulmonary circulation.

    Vena Cava Filter

    If the patient cannot tolerate the anticoagulant therapy or has other conditions that might lead to excessive bleeding, a filter device may be placed in the inferior vena cava (main vein leading to the heart). The filter is introduced with a catheter and positioned within the vena cava to trap large clots before they reach the pulmonary arteries.

    Pulmonary embolectomy (surgical removal of the emboli)

    An embolectomy may be useful for unstable patients with pulmonary embolism when other treatments fail. In surgical embolectomy, an operation is performed to cut open the heart or arteries where the clot is lodged. Catheter-directed pulmonary embolectomy involves inserting a catheter into the femoral or internal jugular vein and using fluoroscopic (x-ray) guidance to navigate into the pulmonary artery. Emboli are then extracted from the pulmonary bed using suction.


    What type of treatment do you recommend?

    If surgery is recommended, what are the risks?

    Can pulmonary embolism recur? If so, should medications be given to lower the risk of recurrence?

    Is the pulmonary embolism attributed to another medical condition?

    If so, what can be done to reduce or eliminate the other condition?

    Are there any preventive measures you recommend?

    Ordinarily, the leg muscles keep blood flowing by compressing the walls of the veins every time you move. This action provides enough energy for the veins to defy gravity and propel the blood back to the heart. When you are immobile for long periods of time the blood begins to pool.

    Your doctor may suggest the following ways to improve circulation:

    • Exercise daily
    • Start a weight reduction plan
    • Do not stand or sit in one position for more than 15 minutes at a time; move your legs frequently; contract and release your buttock and leg muscles often
    • When you sit or lie down, use a stool or pillows to raise your legs
    • Use graduated compression stockings; these stockings help blood move from the legs to the heart by exerting gentle and consistent pressure.
    If you are hospitalized, heparin or another anticoagulant may be given in low doses to prevent clots from forming. In patients who cannot receive anticoagulants, pneumatic compression boots may be placed on the legs. The boots inflate and deflate air-filled cuffs around the legs in slow cycles throughout the day, promoting better blood flow.