Pulmonary Embolism (cont.)

What causes pulmonary embolism?

Major Causes

In 9 out of 10 cases, pulmonary embolism (PE) begins as a blood clot in the deep veins of the leg (a condition known as deep vein thrombosis). The clot breaks free from the vein and travels through the bloodstream to the lungs, where it can block an artery.

Clots in the leg can form when blood flow is restricted and slows down. This can happen when you don't move around for long periods of time, such as:

  • After some types of surgeries

  • During a long trip in a car or on an airplane

  • If you must stay in bed for an extended time

Veins damaged from surgery or injured in other ways are more prone to blood clots.

Other causes

Rarely, an air bubble, part of a tumor, or other tissue travels to the lungs and causes pulmonary embolism. Also, when a large bone in the body (such as the thigh bone) breaks, fat from the marrow inside the bone can travel through the blood to the lungs and cause pulmonary embolism.

Who is at risk for pulmonary embolism?

Populations affected

Pulmonary embolism (PE) occurs equally in men and women. Risk increases with age: For each 10 years after age 60, the risk of pulmonary embolism doubles.

Certain inherited conditions, such as factor V Leiden, increase the risk of blood clotting, and, therefore, the risk of pulmonary embolism.

Major risk factors

People at high risk for a blood clot that travels to the lungs are those who:

  • Have deep vein thrombosis (DVT, a blood clot in the leg) or a history of DVT

  • Have had pulmonary embolism before

Other risk factors

People who recently have been treated for cancer or who have a central venous catheter (a tube placed in a vein to allow easy access to the bloodstream for medical treatment) are more likely to develop DVT. The same is true for people who have been bedridden or have had surgery or suffered a broken bone in the past few weeks.

Other risk factors for DVT, which can lead to pulmonary embolism, include sitting for long periods of time (such as on long car or airplane rides), pregnancy and the 6-week period after pregnancy, and being overweight or obese. Women who take hormone therapy or birth control pills also are at increased risk for DVT.

People with more than one risk factor are at higher risk for blood clots.