A pleural effusion is an abnormal amount of fluid around the lung. Pleural effusions can result from many medical conditions. Most pleural effusions are not serious by themselves, but some require treatment to avoid problems.
Not taking anticoagulant medicine as prescribed, unless your doctor tells you to stop taking it.
Slowed blood flow
When blood does not circulate normally, clots are more likely to develop. Reduced circulation may result from:
Long-term bed rest, such as if you are confined to bed after an operation, injury, or serious illness.
Traveling and sitting for a long time, especially when traveling long distances by airplane.
Leg paralysis. When you use your muscles, the muscles contract, and that squeezes the blood vessels in and around the muscles. The squeezing helps the blood move back toward the heart. Paralysis can reduce circulation because the muscles can't contract.
Some people have blood that clots too easily or too quickly. People with this problem are more likely to form larger clots that can break loose and travel to the lungs. Conditions that may cause increased clotting include:
Inherited factors. Some people have an inherited tendency to develop blood clots that can lead to pulmonary embolism.
Family history of close relatives, such as a sibling, who has had deep vein thrombosis or pulmonary embolism.