Causes and Risk Factors of Pulmonary Embolism

A pulmonary embolus is caused when any foreign material lodges in and obstructs the pulmonary artery or one of its branches. Most commonly, the foreign material is a blood clot that embolizes, but sometimes (rarely) other conditions can be at fault.

Pulmonary embolism is a common medical condition. It often produces serious illness and death and accounts for about 100,000 deaths per year in the United States alone. However, it is associated with several lifestyle risk factors that are within your control.

Pulmonary embolus typically stems from deep vein thrombosis, which can have a variety of causes. If a thrombus (blood clot) that has formed in a major vein breaks off (embolizes), travels through the right side of the heart, and lodges in the pulmonary circulation, it becomes a pulmonary embolus.

Rarer Causes

Rarely, conditions other than deep vein thrombosis can cause a pulmonary embolus that can produce critical illness or death. These other conditions include:

• Fat embolism. A fat embolism can occur if fatty tissue is damaged or manipulated, causing clumps of fat cells to enter the circulation, where they can lodge in the pulmonary circulation. The most common cause of fat embolism is fracture of the pelvis or long bones, whose marrow contains large amounts of fat.
• Air embolism. If air enters the circulation it can occlude a pulmonary artery or other artery. Air embolism can result from almost any type of surgical procedure, or in divers who ascend too rapidly.
• Amniotic fluid embolism. Rarely, amniotic fluid can enter the circulation during difficult childbirth and produce acute pulmonary embolism. This event, fortunately very uncommon, is extremely life-threatening.
• Tumor embolism. If cancer cells enter the circulation in large numbers they can occlude pulmonary vessels. This complication of cancer is usually seen only in people with nearly end-stage disease.

Because a pulmonary embolus is almost always the result of deep vein thrombosis, the risk factors for these two conditions are virtually identical.

These include risk factors related to a person’s lifestyle, including:

• Not getting enough exercise. Being habitually sedentary promotes venous insufficiency, which predisposes to blood clot formation in the major veins.
• Being overweight. Carrying too much weight also promotes pooling of blood in the veins of the lower extremities.
• Smoking. Smoking causes inflammation in the blood vessels, which can lead to excess clotting. In fact, smoking is an especially powerful risk factor for abnormal blood clotting.

In addition to these chronic, lifestyle-related risk factors, there are other conditions that can substantially increase a person’s risk of pulmonary embolus. Some of these risks are temporary or situational in nature; others create a more chronic, long-term risk for pulmonary embolus:

• Recent surgery, hospitalization, or trauma that leads to extended immobilization.
• Long trips that lead to prolonged sitting.
• Trauma that causes tissue damage that may lead to blood clots.
• 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 deep vein thrombosis or or pulmonary embolus in the past.
• Certain genetic conditions can make the blood hypercoagulable (prone to clotting).

Anyone with any of these conditions should make every effort to reduce the risk factors under their control to lower their risk of developing veinous thrombosis and pulmonary embolus. Getting plenty of exercise and keeping weight in control are important; not smoking is critical.