Pulmonary Embolism Information

By Lou Akin

What is a pulmonary embolism?

A pulmonary embolism (PE) is a blood clot that develops in a blood vessel elsewhere in the body (most commonly from the leg), travels to an artery in the lung, and forms an occlusion (blockage) of the artery.

A blood clot (thrombus) that forms in a blood vessel in one area of the body, breaks off, and travels to another area of the body through the bloodstream is called an embolus. An embolus can lodge itself in a blood vessel, blocking the blood supply to a particular organ. This blockage of a blood vessel by an embolus is called an embolism.

An embolism to the lung may cause serious life-threatening consequences and, potentially, death. Most commonly, a PE is the result of a condition called deep vein thrombosis (blood clot in the deep veins of the leg).

The circulatory system

The heart, arteries, capillaries, and veins make up the body's circulatory system. Blood is pumped with great force from the heart into the arteries, then into the capillaries (small blood vessels in the tissues) and returns to the heart through the veins. Much of the force of the heartbeat is lost when the blood enters the veins and results in the slowing down of the blood flow through the veins back to the heart. Under certain conditions, decreased blood flow may contribute to clot formation.

What causes a pulmonary embolism?

Blood clotting is a normal process that occurs in the body to prevent bleeding. The body makes blood clots and then breaks them down. Under certain circumstances, the body may be unable to break down a clot, which may result in a serious health condition.

Abnormal blood clotting in the veins is related to a combination of several problems such as "sluggish" blood flow through the veins, an over-increase in clot forming factors, and/or an injury to the blood vessel wall.

Blood clots can form in arteries and/or veins. Clots formed in veins are called venous clots. Veins of the legs can be classified as superficial veins (close to the surface of the skin) or deep veins (located near the bone and surrounded by muscle).

Venous clots most often occur in the deep veins of the legs. This condition is called deep vein thrombosis (DVT), or deep vein clot. Once a clot has formed in the deep veins of the leg, there is a potential for part of the clot to break off and travel (embolize) through the bloodstream to another area of the body. Deep vein thrombosis is the most common cause of a pulmonary embolism. Therefore, the term venous thromboembolism (VTE) may refer to deep vein thrombosis and/or the complication, pulmonary embolism.

Other less frequent sources of pulmonary embolism are a fat embolus, amniotic fluid embolus, air bubbles, and a deep vein thrombosis in the upper body. Clots may also form on the end of an indwelling intravenous (IV) catheter, break off, and travel to the lungs.

What are the risk factors for pulmonary embolism?

Risk factors that are associated with the processes that may increase the risk of a venous thromboembolism include:

  • Genetic conditions that increase the risk of blood clot formation

  • Surgery or trauma (especially to the legs) or orthopedic surgery

  • Situations in which mobility is limited, such as extended bed rest, flying or riding long distances, or paralysis

  • Previous history of clots

  • Older age

  • Cancer and cancer therapy

  • Certain medical conditions, such as heart failure, chronic obstructive pulmonary disease (COPD), hypertension (high blood pressure), stroke, and inflammatory bowel disease (chronic inflammation of the digestive tract)

  • Certain medications, such as oral contraceptives (birth control pills) and hormone replacement therapy (estrogen pills for postmenopausal women)

  • Pregnancy (during and after pregnancy, including cesarean section)

  • Obesity

  • Varicose veins (enlarged veins in the legs)

  • Cigarette smoking

A risk factor is anything that may increase a person's chance of developing a disease. It may be an activity, such as smoking, diet, family history, or many other things. Different diseases have different risk factors.

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