An Overview of Pulmonary Embolism

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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.

Usually, PE occurs when a blood clot that forms in the legs, a deep vein thrombosis (DVT), dislodges and travels to the blood vessels of the lungs. Symptoms of pulmonary embolism include trouble breathing, chest pain, and coughing up blood. Most people improve with treatment, but up to 30 percent of those who have untreated PE do not survive. With medical treatment, the mortality rate is around 5 percent.

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 most common symptoms of pulmonary embolism are:

  • Shortness of breath, which begins suddenly, usually within a few seconds of PE
  • Sudden, severe chest pain
  • A cough 
  • Coughing up blood
  • Pleuritic chest pain, which is chest pain that is worse when you take a breath
  • Wheezing
  • Low blood pressure, increased heart rate, rapid breathing
  • Blue or pale appearance of the lips and fingers
  • Cardiac arrhythmias (heart rhythm irregularities), such as atrial fibrillation, and related symptoms or severe effects (e.g. lightheadedness, loss of consciousness)
  • Signs or symptoms of DVT in one or both legs

The severity of pulmonary embolism is generally determined by the size of the clot. If a pulmonary embolus 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 embolus 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, 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 percent of people with untreated DVT will experience a pulmonary embolus.

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. 

Predisposition to Forming Excessive Blood Clots 

Most people who have a PE, with or without a preceding DVT, have medical conditions or circumstances associated with blood clotting abnormalities. The most common causes and risk factors for blood clot formation are:

  • Immobility due to physical paralysis, prolonged bed rest, or hospitalization 
  • Sitting for long periods of time during long car rides or airplane plane flights 
  • History of previous pulmonary embolism
  • History of previous blood clots, such as DVT, stroke, or heart attacks
  • Blood clotting disorders
  • Smoking
  • History of cancer and/or use of chemotherapy
  • History of surgery
  • Bone break, especially the femur (thigh) bone
  • Obesity
  • Hormone therapy (including hormone replacement therapy)
  • Birth control pill use
  • Pregnancy or recent pregnancy

Diagnosis

Diagnosis of PE begins with your doctor'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 doctor's estimate of whether your chance of having it is high or low. Your doctor 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 doctor'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 doctor 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 doctor 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 tour 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 doctor 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 noninvasive tests can be confirmed or rule out the diagnosis. If your diagnosis is unclear, you might need to have pulmonary angiography. 

A pulmonary angiogram is a diagnostic test in which dye is injected through a tube into the pulmonary artery so that any blood clots can be visualized on x-ray. Because pulmonary angiography is an invasive test that carries a risk of complications, your doctor will carefully weigh the risks and benefits before recommending this test for you.

Treatment

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

Blood Thinners - Anticoagulants

The main treatment for pulmonary embolus is the use of anticoagulant drugs, blood thinners, to prevent further blood clotting.

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, or fondaparinux. The heparin family of drugs provide an immediate anticoagulant effect and help to prevent further blood clots from forming.

Clot Busters- 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 has been the drug of choice, but in recent years the newer anticoagulation drugs - apixaban (Eliquis), rivaroxaban (Xarelto), edoxaban (Savaysa) and dabigatran (Pradaxa) - have come into widespread use for long-term prevention of recurrent PE.

IVC Filter

If you develop repeated PEs, you might need a filter to be placed in your inferior vena cava, which is the large abdominal vein that connects your leg veins 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.

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. If you experience these complications, you may need to follow up with a pulmonologist to have your breathing function monitored and treated as necessary. 

A Word From Verywell

Pulmonary embolus 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 embolus, such as sudden, unexplained shortness of breath or chest pain, it is important that you get checked by a physician immediately. 

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

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