What Is a Pulmonary Embolism?

Pulmonary embolism (PE) is caused by a blood clot that becomes lodged in the pulmonary artery, the main blood vessel leading to the lungs, or one of its branches.

A blood clot becomes lodged in pulmonary artery.

Usually, PE occurs when a blood clot that forms in the legs, a condition called deep vein thrombosis (DVT), dislodges and travels to the blood vessels of the lungs. Symptoms of PE include trouble breathing, chest pain, and coughing up blood.

Pulmonary Embolism Symptoms 

The pulmonary artery has the critical job of carrying blood to the lungs to be replenished with oxygen, so an obstruction of blood flow within this blood vessel affects the lungs and the heart, and produces symptoms of low oxygen in the rest of the body.

The severity of PE is generally determined by the size of the obstruction. If a pulmonary embolism is large, the case is often described as massive PE. This can cause significant blockage of the pulmonary artery, leading to severe cardiovascular distress, a dangerous drop in blood pressure, and a severe drop in the oxygen content of the blood or oxygen starvation that affects the brain and the rest of the body.

A smaller pulmonary embolism causes less significant symptoms but is still a medical emergency that can be fatal if left untreated. Smaller blood clots generally block one of the smaller branches of the pulmonary artery and may completely occlude a small pulmonary vessel, eventually leading to a pulmonary infarction, which is death of a portion of lung tissue.

Causes

The blood clots, called thromboemboli, that produce a PE are usually caused by DVT in the deep veins of the groin or thighs.

DVT and the Lungs

It is estimated that about 50% of people with untreated symptomatic proximal DVT will develop a symptomatic pulmonary embolism within three months.

The body's anatomy is structured in a way that makes DVTs prone to becoming lodged in the lungs. The veins in the legs, where DVTs tend to form, merge together as blood returns to the right side of the heart through a large vein, the inferior vena cava (IVC). From the right side of the heart, the blood then travels to the lungs via the pulmonary arteries to renew its supply of oxygen.

As a blood clot travels through the veins in the legs to the heart, all of the blood vessels, including those of the heart, are larger than the veins in the legs. When the blood clot enters the lungs, however, the vessels become progressively smaller, and this is where the clots become trapped in one of the pulmonary arteries, leading to PE.

These blood clots may become trapped in any of the blood vessels of the lungs. Small blood clots may become lodged in smaller blood vessels of the lungs. Large blood clots lodge in major blood vessels, interfering with the lungs' ability to adequately oxygenate blood for use throughout the body, with potentially catastrophic consequences. 

Diagnosis

Diagnosis of PE begins with your healthcare provider's clinical evaluation and then may involve specialized tests that can support, confirm, or exclude the diagnosis of PE. 

Clinical Evaluation

The first step in diagnosing PE is your healthcare provider's estimate of whether your chance of having it is high or low. Your healthcare provider makes this estimate by performing a careful medical history, assessing your risk factors for DVT, performing a physical examination, measuring the oxygen concentration in your blood, and possibly doing an ultrasound test to look for a DVT.

Noninvasive Tests

After your healthcare provider's clinical assessment, you might need specific testing, such as blood tests or imaging tests.

• D-dimer test: If your probability of PE is thought to be low, your healthcare provider may order a D-dimer test. The D-dimer test is a blood test that measures whether there has been an abnormal level of clotting activity in your bloodstream, which is expected if you have had a DVT or a PE. If the clinical probability of PE is low and your D-dimer test is negative, a PE can be ruled out, and your healthcare provider will proceed to consider other potential causes of your symptoms.

If your probability of a PE is judged to be high, or if your D-dimer test is positive, then usually either a V/Q scan (ventilation/perfusion scan) or a CT scan of the chest is done.

• V/Q scan: A V/Q scan is a lung scan that uses a radioactive dye, injected into a vein, to assess the flow of blood in your lung tissue. If your pulmonary artery is partially blocked by an embolus, the corresponding part of the lung tissue receives less than the normal amount of the radioactive dye.
• CT scan: The CT scan is a non-invasive, computerized X-ray technique that allows your healthcare provider to visualize your pulmonary arteries to see if you have obstruction caused by an embolus.

Pulmonary Angiogram

A pulmonary angiogram has long been considered the gold standard for identifying a PE, but nowadays there are noninvasive tests that can confirm or rule out the diagnosis. If your diagnosis is unclear, you might need to have pulmonary angiography. 

Treatment

Once a diagnosis of pulmonary embolism is confirmed, therapy is begun immediately. If you have a very high probability of pulmonary embolism, medical therapy may be initiated even before your diagnosis is confirmed. 

Anticoagulants

The blood thinners normally used for the treatment of PE are either IV (intravenous) heparin or a derivative of heparin that can be given by a subcutaneous (under the skin) injection, such as Arixtra (fondaparinux). The heparin family of drugs provide an immediate anticoagulant effect and help to prevent further blood clots from forming.

Thrombolytics

When a PE is large or causes cardiovascular instability, anticoagulation therapy is often not enough. In these situations, powerful clot-busting agents, called thrombolytics, may be injected to dissolve the blood clot. These medications, which include fibrinolytic agents such as streptokinase, are intended to dissolve the blood clot that is obstructing the pulmonary artery.

Thrombolytic therapy carries substantially more risk than therapy with anticoagulants, including a high risk of serious bleeding complications. If the pulmonary embolus is severe enough to be life-threatening, the risk of these therapies may be outweighed by the potential benefits. 

Surgery

Surgery is a method that can directly remove the PE. The most common surgical procedure, called embolectomy surgery, is quite risky and is not always effective, so it is reserved for people who have a very low chance of surviving without it.

Coping

After the initial stage of a PE, you may need a long-term plan to prevent further PEs from occurring, and you may need to adjust to the consequences of your PE if it caused permanent damage. 

Medication

After you have received urgent treatment with an IV blood thinner or an injected clot-busting agent, you might need to take an oral (by mouth) anticoagulant medication for months, or even years. Traditionally Coumadin (warfarin) has been the drug of choice, but in recent years the newer anticoagulation drugs— Eliquis (apixaban), Xarelto (rivaroxaban), Savaysa (edoxaban) and Pradaxa (dabigatran)—have come into widespread use for long-term prevention of recurrent PE.

IVC Filter

If you develop repeated PEs despite taking a blood thinner, you might need a filter to be placed in your inferior vena cava, which is the large abdominal vein that connects your lower body to your heart. An IVC filter can intercept further clots that may break loose from the veins in your legs before they travel to the lungs. The same holds true if you have a complication such as significant bleeding from taking blood thinners.

Pulmonary Follow Up and Rehabilitation

If you experience recurrent PEs, you might develop long-term effects such as pulmonary hypertension or a pulmonary infarction (death) of part of a lung.

A Word From Verywell

Pulmonary embolism is most often seen in people who have a medical condition or circumstances that predispose to DVT. 

If you have symptoms suggestive of a pulmonary embolism, such as sudden, unexplained shortness of breath or chest pain, it is important that you get checked by a healthcare provider immediately. 

Overall, PE is a relatively common condition that has a much better outcome when it is managed with timely treatment.