Pulmonary Embolism (PE)

The sudden blocking of an artery of the lung is not only caused by blood clots. Other material can also form emboli.

Pulmonary infarction is when some of the lung tissue does not receive enough blood flow and oxygen and appears on imaging studies to die due to blockage of a lung blood vessel by a pulmonary embolus. Usually the embolus causing pulmonary infarction is small. The symptoms of pulmonary infarction develop over hours. If pulmonary infarction occurs, the person may cough with blood-stained sputum, sharp chest pain when breathing in, and in some cases fever. Symptoms of infarction often last several days but usually become milder every day.

In those rare people whose emboli persist partly or completely, the blood pressure in the lungs' blood vessels can increase. This increase in blood pressure can cause symptoms, such as shortness of breath, swelling of the ankles or legs, and weakness, which tend to develop progressively over, months, or years.

A chest x-ray Chest Imaging may reveal subtle changes in the blood vessel patterns that occur after embolism and may reveal signs of pulmonary infarction. However, the x‑ray results are often normal, and even when they are abnormal, they rarely enable doctors to establish the diagnosis with certainty.

Electrocardiography Electrocardiography Electrocardiography (ECG) is a quick, simple, painless procedure in which the heart’s electrical impulses are amplified and recorded. This record, the electrocardiogram (also known as an ECG)... read more (ECG) may show abnormalities. These abnormalities can support or suggest the diagnosis of pulmonary embolism but cannot confirm it.

The level of oxygen in the blood is measured with a sensor that is attached to a fingertip (oximetry). Because pulmonary embolism blocks pulmonary arteries, the level of oxygen in the blood may be low. Sometimes doctors also take a sample of blood and measure the level of oxygen and other gases in it.

Doctors first judge how likely pulmonary embolism seems to be, based on information such as the person's risk for pulmonary embolism, the severity of their symptoms, and the results of early tests (such as the chest x-ray and level of oxygen in the blood). Importantly, obvious risk factors may be completely absent.

If pulmonary embolism seems unlikely, a blood test that measures a substance called D‑dimer is typically done. This test may be the only test needed in such people. If in these people the D-dimer level is normal, then the probability that a pulmonary embolus has occurred is extremely low. However, although a low level of D-dimer in such people means that pulmonary embolism is unlikely, a high level does not necessarily mean that pulmonary embolism is likely. Other disorders, such as infection or injury, can cause the D-dimer level to be high so additional testing is needed to confirm the diagnosis.

If pulmonary embolism seems more likely or if the result of the D-dimer test is abnormal, other testing is done, usually one or more of the following:

CT angiography is a type of CT scan. It is fast, noninvasive, and fairly accurate, particularly for large clots. In this test, contrast material is injected into a vein. The contrast material travels to the lungs, and a CT scanner generates images of blood in the arteries to determine if a pulmonary embolism is blocking blood flow. CT angiography is the imaging test most often used to diagnose pulmonary embolism. The size of the heart may also indicate how much the heart is being strained.

A lung ventilation perfusion scan Chest Imaging is noninvasive and fairly accurate but takes longer than a CT scan. A tiny amount of radioactive substance is injected into a vein and travels to the lungs, where it outlines the blood supply (perfusion) of the lung. Completely normal scan results usually indicate that the person does not have a significant blood vessel obstruction. Abnormal scan results support the possibility of pulmonary embolism but may also indicate the possibility of other disorders, such as emphysema, which can result in decreased blood flow to areas where lung tissue has been damaged.

Usually, the perfusion scan is done with a lung ventilation scan. In this test, the person inhales a harmless gas containing a trace amount of radioactive material, which is distributed throughout the small air sacs of the lungs (alveoli). The areas where carbon dioxide is being released and oxygen is taken up can then be seen on a scanner. By comparing this scan to the pattern of blood supply shown on the perfusion scan, doctors can usually determine whether a person has had a pulmonary embolism. Doctors sometimes use a lung perfusion scan if a person has a kidney problem that prevents the use of CT angiography because the contrast material used for the CT might further damage the kidneys.

Ultrasonography of the legs is noninvasive and can identify clots in the legs, which are the usual sources of pulmonary embolism. The absence of clots on this test does not rule out pulmonary embolism. However, if ultrasonography reveals blood clots, and the lung symptoms are minimal, people are occasionally treated as they would be for pulmonary embolism without any further testing, because the treatment for both conditions is often the same.

Pulmonary artery angiography Chest Imaging is very rarely needed to diagnose pulmonary embolism.

Echocardiography may show that a blood clot is in the right atrium or right ventricle of the heart. The results of this test may help doctors determine the severity of the embolism by showing that the right side of the heart is strained by trying to push blood through the clots.

In people who have no apparent risk factors for blood clots or recurring clots, doctors may also measure proteins in the blood to determine whether a clotting disorder is the cause.

For certain people, an anticoagulant drug (also called a blood thinner) is given, most often heparin.

Heparin comes in two forms:

Traditional and low molecular weight heparins appear equally effective. Heparin is the most widely used drug for reducing the likelihood of clots forming in calf veins after any type of major surgery, especially surgery on the legs. Small doses are injected just under the skin, usually within 6 to 12 hours after surgery, and ideally additional doses are given until the person is up and walking again.

Hospitalized people at high risk of developing pulmonary embolism (such as those with heart failure, immobility, or obesity, or who have had clots in the past) benefit from small doses of heparin even if they are not undergoing surgery. Low-dose heparin does not increase the frequency of severe bleeding complications, but heparin can increase minor oozing of blood from wounds.

Warfarin, an anticoagulant given by mouth, is used much less commonly now because when warfarin is used, people need regular blood tests to monitor the effect of warfarin, warfarin interacts with many drugs that people may be taking, and newer drugs are safer and more effective. Low-molecular-weight heparin is more predictable than the standard form of heparin and is commonly used for prevention of clots in people undergoing surgery that has a high risk of causing clots, such as hip or knee replacement.

Newer direct oral anticoagulants include those such as fondaparinux, rivaroxaban, apixaban, edoxaban, and dabigatran that inhibit the formation of substances that enhance the body’s production of clots. These drugs are effective in prevention and in general are safer than warfarin. Nonetheless, warfarin is still considered the best choice for some people such as those with metallic heart valves.

For people who have undergone surgery—especially older people—the risk of clot formation can be reduced by

Intermittent air compression devices are inflatable devices that go over the lower legs and inflate and deflate to provide external pressure to keep blood moving in the legs. However, these devices alone are inadequate to prevent clot formation in people who have undergone certain high risk surgeries such as hip or knee replacement surgery.

Elastic compression stockings provide steady pressure on the blood vessels of the legs to keep blood flowing. They are likely less effective than intermittent compression devices, but still may be helpful in reducing the risk of blood clots in the legs.

In patients who are at high risk of developing pulmonary embolism and who cannot take anticoagulants due to a high risk of bleeding, a filter (called an inferior vena cava filter) may be placed inside a large vein between the heart and the inferior vena cava, which returns blood to the heart from the lower part of the body. A filter can trap emboli, preventing them from reaching the lungs.

Anticoagulant drugs are given to thin the blood, helping blood flow more freely, and thus prevent existing blood clots from enlarging and additional clots from forming. Drug options include heparin, fondaparinux, newer oral anticoagulants, such as apixaban, rivaroxaban, edoxaban, and dabigatran, or occasionally warfarin.

Heparin is given intravenously and therefore works quickly and can be quickly reversed. However, heparin requires frequent blood tests to monitor the effect and continued hospitalization. Low molecular weight heparin and fondaparinux are given subcutaneously once or twice a day. This advantage also allows these drugs to be used after the person is discharged from the hospital.

When edoxaban or dabigatran is used, doctors must give heparin therapy (by vein or by injection under the skin) for the first 5 to 10 days of therapy before they can give the edoxaban or dabigatran, which sometimes means the person must remain in the hospital. In contrast, when rivaroxaban or apixaban is used, heparin therapy is sometimes unnecessary if pulmonary emboli are small. When warfarin therapy is selected, both heparin and warfarin are given for the first 5 to 10 days of therapy, and then warfarin alone is used thereafter.

Warfarin therapy requires periodic blood testing to ensure that the blood is thin enough to prevent clots from forming but not so thin as to cause a bleeding tendency (called excessive anticoagulation). The warfarin dose is frequently adjusted based on the results of the blood tests. Also, warfarin interacts with many different types of food and with other drugs, which can result in blood that is too thin or too thick. If excessive anticoagulation occurs, severe bleeding in a number of body organs can develop.

Because many drugs can interact with warfarin, people who take it should be sure to check with their doctor before taking any other drugs, including drugs that can be obtained without a prescription (over-the-counter drugs) such as acetaminophen or aspirin, herbal preparations, and dietary supplements. Foods that are high in vitamin K (which affects blood clotting), such as broccoli, spinach, kale, and other leafy green vegetables, liver, grapefruit and grapefruit juice, and green tea, may need to be either eaten in very consistent amounts or avoided.

The newer anticoagulants, such as apixaban, rivaroxaban, edoxaban, and dabigatran, have several advantages over heparin or warfarin. Like warfarin, these drugs can be taken by mouth, but dose adjustments and tests to monitor the level of anticoagulation are not needed. Furthermore, these drugs do not often interact with food or other drugs and are less likely to cause severe types of bleeding when compared with warfarin. Rivaroxaban should always be taken with food. It is not clear whether these drugs should be taken by people who are larger than about 120 kg (about 260 lbs).

How long anticoagulants are given depends on the person’s situation. If pulmonary embolism is caused by a temporary risk factor, such as surgery, treatment is given for 3 months. If the cause is some longer-term problem, such as prolonged bed rest, treatment usually is given for 6 to 12 months, but sometimes it must continue indefinitely. For example, people who have recurrent pulmonary embolism, often because of a hereditary clotting disorder or cancer, usually take anticoagulants indefinitely. Newer research studies have shown that in many people in whom rivaroxaban or apixaban are continued after 6 months, reducing the dose decreases risk of bleeding risk and still prevents most recurrent clots.

Thrombolytic drugs ("clot busting drugs") such as alteplase (tPA) break up and dissolve blood clots. Because these drugs can cause dangerous or fatal bleeding, they are usually only used in people who appear to be in danger of dying due to the pulmonary embolism. Except in the most dire situations, these drugs are usually not be given to people who have had surgery in the preceding 2 weeks, are pregnant, have had a recent stroke, or tend to bleed excessively.

In some centers, if a person appears to be in danger of dying from a massive pulmonary embolism, doctors may try to break up the embolus using a catheter inserted into the pulmonary artery.

Surgery may be needed in some cases of severe embolism. Removal of the embolus from the pulmonary artery may be lifesaving. Surgery is also used to remove long-standing pulmonary artery clots that cause persistent shortness of breath and high pressures in the pulmonary artery (pulmonary hypertension Pulmonary Hypertension Pulmonary hypertension is a condition in which blood pressure in the arteries of the lungs (the pulmonary arteries) is abnormally high. Many disorders can cause pulmonary hypertension. People... read more ).

A filter Inferior Vena Cava Filters: One Way to Prevent Pulmonary Embolism can be surgically placed in the main vein in the abdomen that drains blood from the legs and pelvis to the right side of the heart. Such a filter can be used if emboli recur despite anticoagulant treatment or if anticoagulants cannot be used or cause significant bleeding. Because clots generally originate in the legs or pelvis, this filter usually prevents them from being carried into the pulmonary artery. Newer filters are removable. Removal helps prevent some complications that can occur when filters are left in place permanently.