Pulmonary Embolism
(Blood Clot in the Lung)

Medical Author: Benjamin C. Wedro, MD, FAAEM
Medical Editors: George Schiffman, MD and Melissa Conrad Stöppler, MD

• What is a pulmonary embolism?
• What are the causes and risk factors for pulmonary embolism?
• What are the signs and symptoms of pulmonary embolism?
• How is pulmonary embolism diagnosed?
  • History and physical examination
  • Basic testing (CBC, electrolytes, BUN, creatinine blood test, chest x-ray, EKG)
  • Pulmonary angiogram
  • d-Dimer blood test
  • CT Scan
  • Ventilation-perfusion scans
  • Venous Doppler study
  • Echocardiography (EKG, ECG)
• How is pulmonary embolism treated?
  • Anticoagulation
  • Thrombolytic therapy
• What is the prognosis for pulmonary embolism?
• Can pulmonary embolism be prevented?
• Pulmonary Embolism At A Glance

What is a pulmonary embolism?

The lungs are a pair of organs in the chest that are primarily responsible for the exchange of oxygen and carbon dioxide between the air we breathe and blood. The lung is composed of clusters of small air sacs (alveoli) divided by thin, elastic walls (membranes). Capillaries, the tiniest of blood vessels, run within these membranes between the alveoli and allow blood and air to come near each other. The distance between the air in the lungs and the blood in the capillaries is very small, and allows molecules of oxygen and carbon dioxide to transfer across the membranes.

The exchange of the air between the lungs and blood are through the arterial and venous system. Arteries and veins both carry and move blood throughout the body, but the process for each is very different.

• Arteries carry blood from the heart to the body.
  
  
• Veins return blood from the body to the heart.
  
  
• The heart is a two-sided pump.
  
  
• Oxygen-carrying blood travels from the left side of the heart to all the tissues of the body. The oxygen is extracted by the tissue, and carbon dioxide (a waste product) is delivered back into the blood.
  
  
• The blood, now deoxygenated and with higher levels of carbon dioxide, is returned via the veins to the right side of the heart.
  
  
• The blood is then pumped out of the right side of the heart to the lungs, where the carbon dioxide is removed and oxygen is returned to the blood from the air we breathe in, which fills the lungs.
  
  
• Now the blood, high in oxygen and low in carbon dioxide, is returned to the left side of the heart where the process starts all over again.
  
  
• The blood travels in a circle and is therefore referred to as circulation.

If a blood clot (thrombus) forms in the one of the body's veins (deep vein thrombosis or DVT), it has the potential to break off and enter the circulatory system and travel (or embolize) through the heart and  become lodged in the one of the branches of the pulmonary artery of the lung. A clot that travels through the circulatory system to another location is known as an embolus (plural emboli).

A pulmonary embolus clogs the artery that provides blood supply to part of the lung. The embolus not only prevents the exchange of oxygen and carbon dioxide, but it also decreases blood supply to the lung tissue itself, potentially causing lung tissue to die (infarct).

A pulmonary embolus is one of the life-threatening causes of chest pain and should always be considered when a patient presents to a healthcare provider with complaints of chest pain and shortness of breath.

Non-thrombus causes of pulmonary embolus are rare but include:

• fat emboli from a broken femur,
  
  
• an amniotic fluid embolus in pregnancy, and
  
  
• in some cases, tumor tissue from cancer.

The presentation is the same as that of a blood clot, caused by blockage of part of the arterial tree of the lung.

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