Causes and Risk Factors of Pulmonary Embolism

A pulmonary embolus (PE) occurs when material lodges in and obstructs (blocks) the pulmonary artery or one of its branches. Most often, the material is a blood clot, but in rare cases, there may be other causes of the blockage.

Pulmonary embolism is not an uncommon problem. accounting for an estimated 60,000 to 100,000 deaths per year in the United States. It can be caused by certain medical conditions, and several lifestyle risk factors can affect your chances of having a PE.

Common Cause

If a thrombus (blood clot) that has formed in a major vein in the body breaks off, travels through the right side of the heart, and lodges in the pulmonary circulation, it becomes a PE.

Pulmonary embolus typically occurs when a dislodged deep vein thrombosis (DVT) in the arm or leg travels to an artery in the lungs. DVTs have a variety of potential causes.

Rarer Causes

A PE can occur due to other types of blockage besides a DVT.

Less common causes of PE include:

• Fat embolism: A fat embolism can occur if clumps of fat cells enter the circulation, where they can lodge in the pulmonary circulation. The most common cause of fat embolism is a fracture of the pelvis or long bones because the marrow of these bones contains large amounts of fat.
• Air embolism: If air enters the circulation, it can occlude an artery, including the pulmonary artery. Air embolism can result from almost any type of surgical procedure, or it can develop in deep-sea divers who ascend too rapidly.
• Amniotic fluid embolism: Rarely, amniotic fluid can enter the circulatory system during a difficult childbirth, resulting in an acute PE. Amniotic fluid embolism is life-threatening.
• Tumor embolism: Cancer cells that enter the circulation can occlude pulmonary vessels. This is usually an end-stage cancer complication.

Risk Factors

Because a PE is almost always the result of DVT, the risk factors for these two conditions are virtually identical.

These include risk factors related to lifestyle, including:

• Not getting enough exercise: Being chronically sedentary promotes venous insufficiency, which predisposes to blood clot formation in the major veins of the legs.
• Being overweight: Carrying too much weight promotes the pooling of blood in the veins of the lower extremities.
• Smoking: Smoking is an especially powerful risk factor for abnormal blood clots. Smoking causes inflammation in the blood vessels, which can affect blood clotting.

In addition to these chronic, lifestyle-related risk factors, several medical conditions can substantially increase the risk of PE.

Some of these risks are temporary or situational in nature; others create a more chronic, long-term risk:

• Recent surgery, hospitalization, or trauma that leads to extended immobilization
• Long trips that involve prolonged sitting
• Trauma that causes blood clot-inducing tissue damage
• Pregnancy
• Medications, especially birth control pills, hormone replacement therapy, testosterone supplements, tamoxifen, and antidepressants
• Chronic liver disease
• Chronic kidney disease
• Significant cardiovascular disease, especially heart failure
• Having had either DVT or PE in the past
• Certain genetic conditions can make the blood hypercoagulable (prone to clotting)

If you have any of these conditions, you should make every effort to reduce your risk of developing DVT or PE. You may be prescribed medications to prevent your risk of blood clots. Getting plenty of exercise and keeping your weight under control are important; not smoking is critical.