Overview

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 the legs or, rarely, other parts of the body (deep vein thrombosis).
Because the clots block blood flow to the lungs, pulmonary embolism can be lifethreatening. However, prompt treatment greatly reduces the risk of death.

Symptoms

Pulmonary embolism symptoms can vary greatly. Common signs and symptoms include:

Shortness of breath: This symptom typically appears suddenly and always gets worse with exertion.

Chest pain: The pain may become worse when you breathe deeply (pleurisy), cough, eat, bend or stoop. The pain will get worse with exertion but won't go away when you rest.

Cough: The cough may produce bloody or blood-streaked sputum.

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

Leg pain or swelling, or both, usually in the calf

Clammy or discolored skin (cyanosis)

Fever

Excessive sweating

Rapid or irregular heartbeat

Lightheadedness or dizziness

Causes

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. This condition is known as deep vein thrombosis (DVT).
In most cases, multiple clots are involved but not necessarily all at once.

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

Collagen or other tissue

Part of a tumor

Air bubbles

Risk factors

Medical history

You're at higher risk if you or any of your family members have had venous blood clots or pulmonary embolism in the past. This may be due to inherited disorders that affect blood, making it more prone to clot.

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 pancreatic, ovarian and lung cancers, and many cancers with metastasis — can increase levels of substances that help blood clot, 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.

Heart failure: This can result if your heart is pumping ineffectively for a prolonged period due to an arrhythmia, such as atrial fibrillation. Sometimes, controlling the rate of an arrhythmia that's causing heart failure can improve your heart's function.

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.

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 women who smoke or have high blood pressure.

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.

Complications

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. This increases the blood pressure within these vessels and the right side of the heart, which can weaken your heart.

Diagnosis

Pulmonary embolism can be difficult to diagnose, especially in people who have underlying heart or lung disease.

Blood tests

D dimer high levels may suggest an increased likelihood of blood clots, although 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

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 check for blood clots in your thigh veins.
The absence of clots reduces the likelihood of DVT. If the upper thigh vessels are clear, the ultrasonography will also scan the veins behind the knee looking for residual clots. If clots are present, treatment likely will be started immediately.

Spiral CT scan

In a spiral (helical) CT scan, the scanner rotates around your body in a spiral — like the stripe on a candy cane — to create 3-D images. This type of CT can detect abnormalities within the arteries in your lungs with much greater precision than conventional CT scans. In some cases, contrast material is given intravenously during the CT scan to outline the pulmonary arteries.

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 into your heart and on 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.

Treatment

Treatment 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

Blood thinners (anticoagulants): These drugs prevent 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. A newer class of anticoagulants, referred to as novel oral anticoagulants (NOACs), has been tested and approved for treatment of venous thromboembolism, including pulmonary embolism. These medications work quickly and have fewer interactions with other medications. Some NOACs have the advantage of being given by mouth, without the need for overlap with heparin. However, all anticoagulants have side effects, with bleeding being the most common.

Clot dissolvers (thrombolytics): While clots usually dissolve on their own, there are medications given through the vein that 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,

Vein filter: A catheter can also be used to position a filter in the body's main vein — called the inferior vena cava — that leads from your legs to the right side of your heart. This filter can help keep clots from being carried into your lungs. This procedure is typically reserved for people who can't take anticoagulant drugs or when anticoagulant drugs don't work well enough or fast enough. Some filters can be removed when they are no longer needed.