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Pulmonary Embolism

Written by Ada’s Medical Knowledge Team

Updated on

What is a pulmonary embolism?

A pulmonary embolism (PE) is a medical condition which occurs when one or more arteries in the lungs become blocked. When a pulmonary artery becomes blocked, blood flow can be restricted between the heart and the lungs. This can cause serious complications, such as low levels of oxygen in the blood, strain on the heart and damage to the lungs. 1

A blood clot is the most common cause of the blockage. 2 Blood clots most often form in the deep veins of the legs, from where they can detach and travel through the bloodstream towards the lungs, potentially causing a pulmonary embolism.

Symptoms of a pulmonary embolism can arise suddenly or progress gradually over a period of time. 3 If not treated quickly, a significant pulmonary embolism can be life-threatening. The most common symptoms include: 1 4

  • Chest pain that often gets worse when taking deep breaths
  • Shortness of breath
  • Feeling faint
  • Coughing up blood

Treatment for pulmonary embolisms involves removing the blockage, usually through blood-thinning medications, which work to dissolve the blood clot. Surgery may also be recommended in specific cases, such as when medication hasn’t worked or if the person is at a high risk of death from the pulmonary embolism. 5

A pulmonary embolism is a serious condition that can result in significant complications and, in the most severe cases, death. However, with prompt diagnosis and treatment, most people make a full recovery. 6

If you are concerned that you or a loved one may have a pulmonary embolism, contact a doctor without delay. The free Ada app can also be used to carry out a symptom assessment.

Types of pulmonary embolism

Almost all cases of pulmonary embolism result from a blood clot that originates in the legs or pelvis. 7 However, in rare instances, other types of material can also cause a blockage, including: 1 4

  • Air bubbles in the bloodstream, which can occur through activities such as underwater diving, surgery and catheterization
  • Fat, which can enter the bloodstream from bone marrow, usually during surgery or injury
  • Amniotic fluid, which can enter the mother’s bloodstream during a complicated childbirth
  • Cancer cells, which may clump together and enter the bloodstream. This is known as tumor emboli
  • Foreign substances, which may enter the bloodstream, often due to intravenous drug use

Good to know: A blood clot that forms in a vein is also known as a thrombus. An embolus describes any unattached material that travels through the bloodstream. 1

Causes of pulmonary embolism

The pulmonary arteries carry blood from the heart to the lungs. In the lungs, blood is oxygenated before it returns to the heart through the pulmonary veins, where it is then pumped throughout the rest of the body.

A pulmonary embolism is caused when one or more of the pulmonary arteries in the lungs become blocked. This blockage can be solid, liquid or gaseous in nature, but is most often caused by a blood clot. 2

Deep vein thrombosis (DVT)

Almost all pulmonary embolisms are caused by a blood clot that originates in the deep veins of the legs or pelvis. 7 When a blood clot forms in the deep veins of the legs or pelvis, this is a condition known as deep vein thrombosis (DVT). A pulmonary embolism is caused when a blood clot, or part of a blood clot, breaks off and travels through the bloodstream, eventually causing a blockage in the arteries of the lungs. 4

Symptoms of pulmonary embolism

The severity of a pulmonary embolism generally depends on a number of factors, including: 1 2 4 8

  • The size of the blockage
  • Where in the pulmonary arteries the blockage is
  • The overall health of the affected person
  • The age of the affected person
  • The gender of the affected person

The main symptoms that may indicate pulmonary embolism are: 1 2 4

  • Chest pain that often gets worse when taking deep breaths
  • Shortness of breath
  • Fast breathing
  • Fast heart rate
  • Feeling faint and dizzy

Further possible symptoms of pulmonary embolism can include: 1 2 3 4 7

  • Coughing, including coughing up blood
  • Feelings of anxiousness
  • Low blood pressure, also known as hypotension
  • Fever
  • Fainting
  • Painful leg swelling, if the cause is a clot in the leg

Symptoms typically appear over a number of hours or days and can vary in frequency and intensity. 9 Some people with a pulmonary embolism may even be asymptomatic, i.e. not experience any symptoms at all. 3 7

Significant pulmonary embolisms can be life-threatening if not treated quickly. It is recommended that any person who suspects they have a pulmonary embolism contact their doctor immediately.

Good to know: Because the signs of pulmonary embolism are so variable and many of the symptoms are shared with other conditions, diagnosis can be difficult. A doctor may suspect a pulmonary embolism after monitoring a person’s symptoms and noting any risk factors, but will then rely on a number of tests to help diagnose the condition. 1

Worried that you or a loved one may have a pulmonary embolism? Always contact a doctor when a pulmonary embolism is suspected. You can also download the free Ada app to carry out a symptom assessment.

Risk factors for pulmonary embolism

It is estimated that pulmonary embolisms affects around 350,000 people in the United States every year. 7 Because pulmonary embolisms are so often caused by blood clots, the risk factors for developing blood clots and experiencing a pulmonary embolism are often shared. It is estimated that 40-50 percent of people with deep vein thrombosis develop a pulmonary embolism. 10 Risk factors for pulmonary embolism include: 1 ref2 5 9 11 12 13

  • Age over 60 years old
  • Prolonged periods of inactivity, that may be due to reduced mobility, such as after surgery or long travel
  • Certain medical conditions, such as cancer and blood clotting disorders
  • Family history of blood clots or embolisms
  • Previous instances of deep vein thrombosis (DVT)
  • Major surgery or injury within the last four weeks
  • Pregnancy
  • Smoking
  • Obesity
  • Estrogen-containing oral contraceptive pills have been linked to an increased risk of developing blood clots. However, the risk of developing a pulmonary embolism due to oral contraceptive pills is low, particularly in young, non-smoking people.

Diagnosing pulmonary embolism

A doctor may suspect a pulmonary embolism based on a person’s symptoms and a physical examination, but further diagnostic tests are typically needed to confirm the diagnosis. 4

Many diseases and illnesses that affect the heart and lungs share at least one symptom with pulmonary embolisms, such as chest pain, shortness of breath or increased heart rate. Therefore, doctors will need to rule out other conditions that can cause similar symptoms, such as temporary lung changes that can happen after surgery, pneumonia and acute heart failure. 14

Wells criteria for pulmonary embolism

When considering the diagnosis of a pulmonary embolism, a doctor will typically check a person’s symptoms against a points-based clinical criteria known as Wells criteria. According to this criteria, certain symptoms and circumstances receive a specific numerical point score. Examples include: 2

  • Clinical symptoms of deep vein thrombosis – score of 3
  • Previous instance of pulmonary embolism or deep vein thrombosis – score of 1.5
  • Coughing up blood – score of 1

The final score a person receives helps a doctor to assess the overall likelihood of a pulmonary embolism. In turn, this can influence which diagnostic tests may be most suitable for them. 3

Imaging tests

A definitive diagnosis of pulmonary embolism can often be made through a CT scan. 2 A CT scan is a non-invasive imaging test that uses X-rays in multiple layers to gain a view of the inside of the body.

A version of this, called CT angiography, is the imaging test most often used to diagnose a pulmonary embolism because it can generate a detailed view of the pulmonary arteries in the lungs. During CT angiography, a contrast dye is injected into the person’s veins. Once the dye has traveled through the bloodstream to the blood vessels of the lungs, a CT scanner will be used to generate an internal image of the body. Because the dye shows up clearly on the scan, any evidence of an obstruction in the pulmonary arteries is usually very apparent. 1

Other imaging tests that might be suggested include: 1 2 4 15

Pulmonary ventilation/perfusion scans, also known as a V/Q scan, are often suggested as an alternative to CT angiography when CT angiography is not available or appropriate. A V/Q scan measures the air and blood flow in the lungs. It involves imaging the lungs with a special device after a person has inhaled a radiolabeled gas and once a radiolabeled dye has been injected into a person’s veins. Radiolabeling is a technique whereby a gas or liquid is joined by a radioactive substance, allowing its passage through the human body to be tracked.

Chest X-ray is not often used to diagnose pulmonary embolism. However, it can be useful in ruling out other possible causes of the symptoms, such as pneumonia.

Pulmonary angiography is usually only conducted if CT angiography is not available. It involves threading a catheter into the pulmonary artery via a small cut in the skin. A dye is then injected into the artery through the catheter, and X-ray images are taken to monitor flow through the pulmonary artery.

Laboratory tests

Blood tests are sometimes recommended as a diagnostic method for a suspected pulmonary embolism. Blood tests usually cannot confirm a diagnosis, but they may help to support or exclude a diagnosis. 3

For example, a blood test that measures a substance called the D-dimer is often suggested for people who are thought to have a low to moderate probability of a pulmonary embolism. If the level of the D-dimer in the blood is normal, then the likelihood of pulmonary embolism is very low and diagnosis can often be ruled out. 2

Other tests

Further diagnostic tests that may be suggested to help support or exclude the diagnosis of a pulmonary embolism include: 1 2 3 4

  • Electrocardiogram (ECG). An ECG uses sensors attached to the body to monitor the heart’s electrical activity
  • Echocardiogram uses soundwaves to generate an image of the heart
  • Ultrasound tests can use sound waves to detect clots in the legs, which are the usual source of a pulmonary embolism

Good to know: A CT angiography is considered the gold standard test to definitively diagnose a pulmonary embolism. While the majority of other tests may help to support a diagnosis, they typically cannot be used to confirm or rule out the condition. Therefore, a doctor may recommend a combination of diagnostic tests, guided by the affected person’s symptoms, history and score in the Wells criteria for pulmonary embolism.

Treatment of pulmonary embolism

** A pulmonary embolism is often a medical emergency.**
Treatment depends on the severity of the blockage, but usually focuses on three stages:

  • Making sure the affected person is stable by treating the most serious symptoms first. For example, providing oxygen to someone with trouble breathing
  • Treating the blockage, which is usually accomplished by medications
  • Taking steps to prevent future clots, including lifestyle changes and, potentially, medication

Symptomatic treatment

Pulmonary embolisms can cause potentially life-threatening symptoms, such as breathing problems and dangerously low blood pressure. Therefore, immediate treatment for a pulmonary embolism often focuses on treating these symptoms with treatment methods such as: 1 2 16

  • Additional oxygen, often given through a face mask or nasal tubes, to increase the amount of oxygen that reaches the lungs and raise the levels of oxygen in the blood
  • Extra fluids, often through an intravenous drip, to help raise blood pressure
  • Mechanical ventilation to assist breathing. It may be necessary if respiratory failure develops
  • Pain-relief medication, such as acetaminophen/paracetamol and nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen

Treating the blockage

Once a person has been stabilized, doctors will usually move onto treating the blockage itself. This is usually done through attempts to either dissolve or physically remove the blockage.


If the cause of the blockage is a blood clot, immediate medication is generally required to thin the blood and dissolve the clot. Such medication is typically delivered intravenously and in hospital.

The medication prescribed depends on the severity of the blockage, but usually falls into one of two categories: 1 5 17

Anticoagulants. Also known as blood-thinners, anticoagulant medication helps to prevent any existing blood clots from enlarging and also prevents new blood clots from forming. Different anticoagulation medications can be used for initial treatment as well as for longer-term therapy. Anticoagulants are often prescribed for at least three months following a pulmonary embolism. 2

At first, anticoagulant medications are usually administered intravenously, which means the medicine is injected directly into the veins or subcutaneously, which means injected just under the skin. However, long-term anticoagulant medications are often taken orally as a tablet.

Thrombolytics. Also known as clot-busters, thrombolytic medication is only prescribed for life-threatening cases of pulmonary embolism. Thrombolytics work quickly to dissolve blood clots. However, they carry the risk of causing significant bleeding, which is why they are only administered in emergency situations. Thrombolytic medications are usually administered intravenously.

Good to know: In recent years, a device called the <em>EkoSonic Endovascular System</em> has been shown to be effective at accelerating thrombolytic therapy in a procedure called ultrasound-accelerated thrombolysis (UAT). This procedure uses a catheter that emits ultrasound waves in conjunction with the release of thrombolytic medication. The ultrasound waves are believed to help the drugs to penetrate and dissolve the clots more easily. 7 18 This technology can also possibly be used, without medication, in treatment of a pulmonary embolism in high-risk patients with active bleeding, who may not be suitable for thrombolytic therapy.


Pulmonary embolisms rarely require surgery, as medication is typically sufficient to treat the condition. However, in emergency situations where other treatment methods are either unavailable, unsuitable or have been unsuccessful, surgery to remove the clot may be suggested. This procedure is known as an embolectomy and can be conducted in two ways: 2 5

  • Surgical embolectomy, where an incision is made into the pulmonary artery and the blood clot is surgically removed.
  • Catheter embolectomy, where a catheter is threaded into the blood vessel via a small incision in the skin. Attempts to break up and remove the clot can then be made by using instruments or suction pads attached to the end of the catheter.

Preventing pulmonary embolism

A pulmonary embolism is a potentially life-threatening condition and therefore, preventive measures are often recommended to people who are believed to be at higher risk of developing the condition.

Certain medications and lifestyle changes can be beneficial in helping to prevent pulmonary embolisms. The precise measures suggested by a doctor will depend on the person themselves, their specific risk factors and overall health of the person. 1

Preventive medication

People who are at risk of developing blood clots, or deep vein thrombosis, may need to take blood thinning medications, known as anticoagulants. An oral anticoagulant called warfarin, also known as coumadin, is often prescribed for this purpose as it can reduce the likelihood of blood clots from forming. 1

The use of medication as a preventive measure against any health condition is called prophylactic treatment. As the majority of pulmonary embolisms occur in ill people, it is particularly common for anticoagulant prophylaxis to be recommended within the following groups: 1 17

  • Hospitalized people who are at high risk of developing pulmonary embolisms, e.g. those with reduced mobility or who have had blood clots in the past
  • Hospitalized patients who have recently undergone major surgery, particularly surgery to the legs
  • People suffering from cancer
  • People with certain medical conditions, such as blood clotting disorders

Inferior vena cava filter

If medication is not an option or has been unsuccessful, a filter may be placed inside the large vein that carries blood from the lower body to the heart as treatment for a pulmonary embolism. This is known as an inferior vena cava filter.

An inferior vena cava filter works by trapping any blood clots that have formed in the lower body and are circulating through the bloodstream, thereby preventing them from reaching the lungs and potentially causing a pulmonary embolism. Blood can continue to flow freely through the filter.

Good to know: Use of IVC filters is not routine, but they can be used to both prevent and treat pulmonary embolisms in people who cannot take anticoagulation medication, who have developed pulmonary embolisms despite of the use of anticoagulants, or those who have experienced complications of an anticoagulant. 11 17


A number of lifestyle measures can also be used to help prevent the likelihood of a blood clot forming. These include: 1 4 5 17

  • Physical activity. Getting up and moving around, particularly in people who are prone to clotting. Even light activities, such as sitting, standing and walking can be beneficial.
  • Compression socks. Wearing elastic compression socks can help aid blood circulation by placing light pressure on the blood vessels in the legs.
  • Air compression devices. An inflatable cuff that wraps around the leg or foot can also place external pressure on the blood vessels and aid circulation.
  • Stopping smoking, because smoking increases the risk of developing blood clots.

Complications of pulmonary embolism

With swift diagnosis and treatment of a pulmonary embolism, most people make a full recovery. However, a severe pulmonary embolism can cause significant complications, particularly to the lungs and heart. Potential complications of a pulmonary embolism include: 2 9 11

  • Cardiac arrest, where the heart stops beating and pumping blood around the body
  • Heart attack, where the blood supply to the heart muscle becomes blocked, often by a blood clot
  • Heart failure, where the heart cannot pump blood around the body effectively
  • Obstructive and cardiogenic shock, both of which occur when the heart cannot pump sufficient oxygenated blood around the body
  • Lung infarction, also known as pulmonary infarction, where part of the lung dies due to blocked blood supply
  • Pneumonia, an infection in the lungs, which can arise following lung infarction
  • Atelectasis, where the air sacs in the lung, also known as alveoli, collapse and cannot expand properly. This is, however, very commonly reversible once the blockage is removed and the person is breathing normally again
  • Lung effusion, also known as a pleural effusion, is a buildup of fluid around the lungs
  • Pulmonary hypertension, high blood pressure in the pulmonary arteries
  • Irregular heartbeat, also known as a heart arrhythmia
  • Hypoxemia, low levels of oxygen in the bloodstream

Once a pulmonary embolism has occurred, there is a high rate of recurrence if preventive measures are not taken. Without anticoagulation treatment, it is believed that the recurrence rate is 10 percent the year after the initial pulmonary embolism and 5 percent per year after. 2

Good to know: Prompt diagnosis and treatment is very important in cases of pulmonary embolism, as it can cause a number of serious health complications and even result in death. It can also make other existing health conditions, such as heart failure, worse. Always contact a doctor immediately if a pulmonary embolism is suspected.

Other names for pulmonary embolism

  • PE
  • Venous thromboembolism (VE)
  • Blood clot in the lungs
  • Pulmonary thromboembolism

Pulmonary embolism FAQs

Q: What is the difference between a pulmonary embolism and a deep vein thrombosis?
A: A pulmonary embolism is when a blockage occurs in the pulmonary arteries, the arteries that carry blood from the heart to the lungs. Often, the blockage is caused by a blood clot that has formed elsewhere in the body and then traveled through the bloodstream to the lungs. A serious blockage can be life-threatening if not treated quickly.

A deep vein thrombosis is when a blood clot forms in one of the deep veins of the legs or pelvis. This can lead to swelling and discomfort in the legs. However, if the blood clot breaks off into the bloodstream and reaches the lungs, it can cause a pulmonary embolism. Deep vein thromboses are the most common cause of pulmonary embolisms. 4

Q: Can a pulmonary embolism occur during pregnancy?
A: Yes. Pregnant people are around 10 times more likely to develop a blood clot than non-pregnant people. 19 However, the overall prevalence of blood clots in pregnancy is still low, only occurring in approximately 1 in every 1,600 pregnancies. 20

If a pulmonary embolism is suspected during pregnancy, the preferred diagnostic method is usually a pulmonary ventilation/perfusion scan (V/Q scan), where a contrast dye is injected into the bloodstream, and the lungs are scanned to visualize any blockages. 19

Q: How is pulmonary embolism treated during pregnancy?
A: The blood-thinning drug, low molecular weight heparin (LMWH), is typically used to treat pulmonary embolism in pregnancy. This is generally administered as an injection, and treatment may continue for at least six weeks after birth. LMWH is a commonly used anticoagulant and is considered safe to use during pregnancy. 19

Q: What is a saddle pulmonary embolism?
A: A saddle pulmonary embolism is a large clot that lodges in the pulmonary trunk, the main blood vessel that carries blood out of the heart to the lungs. This large clot straddles the area where the pulmonary trunk splits into the right and left pulmonary arteries.

A pulmonary embolism typically only occurs in one pulmonary artery at a time. However, in a saddle pulmonary embolism, the blockage can extend into both pulmonary arteries and is known as a bilateral pulmonary embolism. Saddle pulmonary embolisms are rare and are usually medium to high-risk. 7 21 22