Pulmonary embolism is a blockage in one of the pulmonary arteries in your lungs. In most cases, pulmonary embolism is caused by blood clots that travel to the lungs from deep veins in the legs or, rarely, from veins in other parts of the body (deep vein thrombosis).

Because the clots block blood flow to the lungs, pulmonary embolism can be life-threatening. However, prompt treatment greatly reduces the risk of death. Taking measures to prevent blood clots in your legs will help protect you against pulmonary embolism.

Pulmonary embolism symptoms can vary greatly, depending on how much of your lung is involved, the size of the clots, and whether you have underlying lung or heart disease.

Common signs and symptoms include:

• Shortness of breath. This symptom typically appears suddenly and always gets worse with exertion.
• Chest pain. You may feel like you're having a heart attack. The pain is often sharp and felt when you breathe in deeply, often stopping you from being able to take a deep breath. It can also be felt when you cough, bend or stoop.
• Cough. The cough may produce bloody or blood-streaked sputum.

Other signs and symptoms that can occur with pulmonary embolism include:

• Rapid or irregular heartbeat
• Lightheadedness or dizziness
• Excessive sweating
• Fever
• Leg pain or swelling, or both, usually in the calf caused by a deep vein thrombosis
• Clammy or discolored skin (cyanosis)

When to see a doctor

Pulmonary embolism can be life-threatening. Seek urgent medical attention if you experience unexplained shortness of breath, chest pain or a cough that produces bloody sputum.

Pulmonary embolism occurs when a clump of material, most often a blood clot, gets wedged into an artery in your lungs. These blood clots most commonly come from the deep veins of your legs, a condition known as deep vein thrombosis (DVT).

In many cases, multiple clots are involved in pulmonary embolism. The portions of lung served by each blocked artery are robbed of blood and may die. This is known as pulmonary infarction. This makes it more difficult for your lungs to provide oxygen to the rest of your body.

Occasionally, blockages in the blood vessels are caused by substances other than blood clots, such as:

• Fat from the marrow of a broken long bone
• Part of a tumor
• Air bubbles

Although anyone can develop blood clots and subsequent pulmonary embolism, certain factors can increase your risk.

Medical conditions and treatments

You're at higher risk if you or any of your family members have had venous blood clots or pulmonary embolism in the past.

In addition, some medical conditions and treatments put you at risk, such as:

• Heart disease. Cardiovascular disease, specifically heart failure, makes clot formation more likely.
• Cancer. Certain cancers — especially brain, ovary, pancreas, colon, stomach, lung and kidney cancers, and cancers that have spread — can increase the risk of blood clots, and chemotherapy further increases the risk. Women with a personal or family history of breast cancer who are taking tamoxifen or raloxifene also are at higher risk of blood clots.
• Surgery. Surgery is one of the leading causes of problem blood clots. For this reason, medication to prevent clots may be given before and after major surgery, such as joint replacement.
• Disorders that affect clotting. Some inherited disorders affect blood, making it more prone to clot. Other medical disorders such as kidney disease can also increase your risk of blood clots.
• Coronavirus disease 2019 (COVID-19). People who have severe symptoms of COVID-19 have an increased risk of pulmonary embolism.

Prolonged immobility

Blood clots are more likely to form during periods of inactivity, such as:

• Bed rest. Being confined to bed for an extended period after surgery, a heart attack, leg fracture, trauma or any serious illness makes you more vulnerable to blood clots. When the lower extremities are horizontal for long periods, the flow of venous blood slows and blood can pool in the legs, sometimes resulting in blood clots.
• Long trips. Sitting in a cramped position during lengthy plane or car trips slows blood flow in the legs, which contributes to the formation of clots.

Other risk factors

• Smoking. For reasons that aren't well understood, tobacco use predisposes some people to blood clot formation, especially when combined with other risk factors.
• Being overweight. Excess weight increases the risk of blood clots — particularly in people with other risk factors.
• Supplemental estrogen. The estrogen in birth control pills and in hormone replacement therapy can increase clotting factors in your blood, especially if you smoke or are overweight.
• Pregnancy. The weight of the baby pressing on veins in the pelvis can slow blood return from the legs. Clots are more likely to form when blood slows or pools.

Pulmonary embolism can be life-threatening. About one-third of people with undiagnosed and untreated pulmonary embolism don't survive. When the condition is diagnosed and treated promptly, however, that number drops dramatically.

Pulmonary embolism can also lead to pulmonary hypertension, a condition in which the blood pressure in your lungs and in the right side of the heart is too high. When you have obstructions in the arteries inside your lungs, your heart must work harder to push blood through those vessels, which increases blood pressure and eventually weakens your heart.

In rare cases, small emboli occur frequently and develop over time, resulting in chronic pulmonary hypertension, also known as chronic thromboembolic pulmonary hypertension.

Preventing clots in the deep veins in your legs (deep vein thrombosis) will help prevent pulmonary embolism. For this reason, most hospitals are aggressive about taking measures to prevent blood clots, including:

• Blood thinners (anticoagulants). These medications are often given to people at risk of clots before and after an operation — as well as to people admitted to the hospital with medical conditions, such as heart attack, stroke or complications of cancer.
• Compression stockings. Compression stockings steadily squeeze your legs, helping your veins and leg muscles move blood more efficiently. They offer a safe, simple and inexpensive way to keep blood from stagnating during and after general surgery.
• Leg elevation. Elevating your legs when possible and during the night also can be very effective. Raise the bottom of your bed 4 to 6 inches (10 to 15 cm) with blocks or books.
• Physical activity. Moving as soon as possible after surgery can help prevent pulmonary embolism and hasten recovery overall. This is one of the main reasons your nurse may push you to get up, even on your day of surgery, and walk despite pain at the site of your surgical incision.
• Pneumatic compression. This treatment uses thigh-high or calf-high cuffs that automatically inflate with air and deflate every few minutes to massage and squeeze the veins in your legs and improve blood flow.

Prevention while traveling

The risk of blood clots developing while traveling is low, but increases as long-haul travel increases. If you have risk factors for blood clots and you're concerned about travel, talk with your doctor.

Your doctor might suggest the following to help prevent blood clots during travel:

• Drink plenty of fluids. Water is the best liquid for preventing dehydration, which can contribute to the development of blood clots. Avoid alcohol, which contributes to fluid loss.
• Take a break from sitting. Move around the airplane cabin once an hour or so. If you're driving, stop every so often and walk around the car a couple of times. Do a few deep knee bends.
• Fidget in your seat. Flex your ankles every 15 to 30 minutes.
• Wear support stockings. Your doctor may recommend these to help promote circulation and fluid movement in your legs. Compression stockings are available in a range of stylish colors and textures. There are even devices, called stocking butlers, to help you put on the stockings.

Pulmonary embolism can be difficult to diagnose, especially in people who have underlying heart or lung disease. For that reason, your doctor will likely discuss your medical history, do a physical exam, and order one or more of the following tests.

Blood tests

Your doctor may order a blood test for the clot-dissolving substance D dimer. High levels may suggest an increased likelihood of blood clots, although many other factors can also cause high D dimer levels.

Blood tests also can measure the amount of oxygen and carbon dioxide in your blood. A clot in a blood vessel in your lungs may lower the level of oxygen in your blood.

In addition, blood tests may be done to determine whether you have an inherited clotting disorder.

Chest X-ray

This noninvasive test shows images of your heart and lungs on film. Although X-rays can't diagnose pulmonary embolism and may even appear normal when pulmonary embolism exists, they can rule out conditions that mimic the disease.

Ultrasound

A noninvasive test known as duplex ultrasonography (sometimes called duplex scan or compression ultrasonography) uses sound waves to scan the veins in your thigh, knee and calf, and sometimes in your arms, to check for deep vein blood clots.

A wand-shaped device called a transducer is moved over the skin, directing the sound waves to the veins being tested. These waves are then reflected back to the transducer to create a moving image on a computer. The absence of clots reduces the likelihood of deep vein thrombosis. If clots are present, treatment likely will be started immediately.

CT pulmonary angiography

CT scanning generates X-rays to produce cross-sectional images of your body. CT pulmonary angiography ― also called CT pulmonary embolism study ― creates 3D images that can detect abnormalities such as pulmonary embolism within the arteries in your lungs. In some cases, contrast material is given intravenously during the CT scan to outline the pulmonary arteries.

Ventilation-perfusion scan (V/Q scan)

When there is a need to avoid radiation exposure or contrast from a CT scan due to a medical condition, a V/Q scan may be performed. In this test, a tracer is injected into a vein in your arm. The tracer maps blood flow (perfusion) and compares it with the airflow to your lungs (ventilation) and can be used to determine whether blood clots are causing symptoms of pulmonary hypertension.

Pulmonary angiogram

This test provides a clear picture of the blood flow in the arteries of your lungs. It's the most accurate way to diagnose pulmonary embolism, but because it requires a high degree of skill to administer and has potentially serious risks, it's usually performed when other tests fail to provide a definitive diagnosis.

In a pulmonary angiogram, a flexible tube (catheter) is inserted into a large vein — usually in your groin — and threaded through your heart and into the pulmonary arteries. A special dye is then injected into the catheter, and X-rays are taken as the dye travels along the arteries in your lungs.

In some people, this procedure may cause a temporary change in heart rhythm. In addition, the dye may cause increased risk of kidney damage in people with reduced kidney function.

MRI

MRI is a medical imaging technique that uses a magnetic field and computer-generated radio waves to create detailed images of the organs and tissues in your body. MRI is usually reserved for pregnant women (to avoid radiation to the fetus) and people whose kidneys may be harmed by dyes used in other tests.

Treatment of pulmonary embolism is aimed at keeping the blood clot from getting bigger and preventing new clots from forming. Prompt treatment is essential to prevent serious complications or death.

Medications

Medications include different types of blood thinners and clot dissolvers.

• Blood thinners (anticoagulants). These drugs prevent existing clots from enlarging and new clots from forming while your body works to break up the clots. Heparin is a frequently used anticoagulant that can be given through the vein or injected under the skin. It acts quickly and is often overlapped for several days with an oral anticoagulant, such as warfarin, until it becomes effective, which can take days.

  Newer oral anticoagulants work more quickly and have fewer interactions with other medications. Some have the advantage of being given by mouth, without the need for overlap with heparin. However, all anticoagulants have side effects, and bleeding is the most common.

• Clot dissolvers (thrombolytics). While clots usually dissolve on their own, sometimes thrombolytics given through the vein can dissolve clots quickly. Because these clot-busting drugs can cause sudden and severe bleeding, they usually are reserved for life-threatening situations.

Surgical and other procedures

• Clot removal. If you have a very large, life-threatening clot in your lung, your doctor may suggest removing it via a thin, flexible tube (catheter) threaded through your blood vessels.
• Vein filter. A catheter can also be used to position a filter in the body's main vein (inferior vena cava) that leads from your legs to the right side of your heart. This filter can help keep clots from going to your lungs. This procedure is typically reserved for people who can't take anticoagulant drugs or when they have had recurrent clots despite use of anticoagulants. Some filters can be removed when no longer needed.

Ongoing care

Because you may be at risk of another deep vein thrombosis or pulmonary embolism, it's important to continue treatment, such as remaining on blood thinners, and be monitored as often as suggested by your doctor. Also, keep regular doctor visits to prevent or treat complications.

Pulmonary embolism is often initially evaluated in hospitals, emergency rooms or urgent care centers. If you think you might have a pulmonary embolism, seek immediate medical attention.

What you can do

You may want to prepare a list that includes:

• Detailed descriptions of your symptoms
• Information about your past medical problems, especially any recent surgeries or illnesses that kept you bedridden for several days
• Details on any recent journeys that involved long car or plane rides
• All medications you're taking, including vitamins, herbal products and any other supplements, and the dosages
• Information about the medical problems of parents or siblings
• Questions you want to ask the doctor

What to expect from your doctor

During the physical exam, your doctor will likely inspect your legs for evidence of a deep vein clot — an area that's swollen, tender, red and warm. He or she will also listen to your heart and lungs and check your blood pressure, and will likely order one or more tests.