Causes and Risk Factors for DVT & Pulmonary Embolism
Although deep venous thrombosis may develop with no known cause, it often occurs as a result of conditions following surgery (e.g., reduced blood flow, damage to the lining of a vein). Once a blood clot forms, the clot or a portion of the clot may break away and travel to the lung, resulting in a pulmonary embolism. Risk for these conditions increases with age.
There are a number of risk factors for deep vein thrombosis. People who have more than one risk factor at the same time are at even greater risk. Immobility (e.g., following an injury or surgery) and blood clotting disorders (called thrombophilia or hypercoagulable state) are primary risk factors. The most common type of genetic (inherited) thrombophilia is factor V Leiden, which also increases the risk for pregnancy complications.
Other factors that increase the risk for DVT include the following:
- Cancer and cancer treatment
- Pregnancy and the postpartum period (weeks following giving birth)
- Hormone therapy (e.g., birth control pills)
- Sitting for long periods of time (e.g., in the car, on a plane)
- Varicose veins
Patients who have a central venous catheter, which is a catheter in the major vein from the upper body (called the vena cava superior), have a higher risk for DVT.
Deep venous thrombosis is a risk factor for pulmonary embolism. Rarely, pulmonary embolism also can occur when an air bubble in the circulatory system (called an air embolism) or other tissue (e.g., tumor, bone marrow tissue) travels to the lung.
Air can be introduced into the bloodstream system during surgery, or as a result of trauma (e.g., a car accident that damages the lungs), or as a complication of pregnancy. In some cases, tumor cells break away from the primary tumor and enter the bloodstream, forming a clot. A severe fracture of a large bone in the body (e.g., the thighbone [femur]) can cause bone marrow tissue to enter the circulatory system and travel to the lung.
DVT & Pulmonary Embolism Signs and Symptoms
Symptoms of DVT vary, depending on the location and severity of the blood clot. In as many as 50% of patients who have the condition, DVT is asymptomatic (i.e., does not cause symptoms). In some cases, patients are not aware that they have DVT until the blood clot travels to the lung and causes pulmonary embolism.
Signs of deep venous thrombosis include the following:
- Swelling (edema)
- Pain or tenderness
- Redness or discoloration
Some patients with DVT experience pain in the calf when the foot is flexed upward (called Homan's sign). However, this sign also can be associated with other conditions and is not present in all patients with DVT.
Symptoms of pulmonary embolism include chest pain, shortness of breath (dyspnea), cough, and low-grade fever (about 101°F). In some cases, patients who have a pulmonary embolism cough up blood (called hemoptysis). The condition also can cause feelings of restlessness and apprehension, and an irregular heart rate (arrhythmia).
Complications of Deep Vein Thrombosis (DVT) & Pulmonary Embolism
Sometimes lung tissue is damaged as a result of a pulmonary embolism that blocks blood flow and deprives the tissue of oxygen. This does not happen often because the lungs have three sources of oxygen. These sources include air flow within the large passages that connect the windpipe to the lungs (bronchi), blood flow within the bronchi, and blood flow within the lungs themselves.