Pleural Effusion

The pleura is the thin membrane that lines the inside of the chest wall and covers the lungs. There is normally a tiny amount of fluid between the two layers of pleura. This acts like lubricating oil between the two lungs and the chest wall as they move when breathing. A pleural effusion develops when this fluid builds up and separates the lung from the chest wall.


You may feel some chest pain but a pleural effusion is often painless. The amount of fluid varies. As the effusion becomes larger, it presses on the lung which cannot expand fully when your breathe. You may then become breathless.

You may also have symptoms of the condition that is causing the effusion. (for example, cough, chest pain and fever with pneumonia.)


A pleural effusion is a complication of a variety of conditions. These include the following:

  • Pneumonia, tuberculosis, other lung infections and tumours (cancers) may cause inflammation of the lung and pleura. This may cause fluid to build up into a pleural effusion
  • Some arthritic conditions may cause inflammation of the pleura in addition to joint inflammation. For example, pleural effusion is an uncommon complication of rheumatoid arthritis
  • Heart failure causes ‘back pressure’ in the blood vessels (veins) that take blood back to the heart
  • Some fluid may seep out of the blood vessels. Swelling of the legs with fluid is typical with heart failure but a pleural effusion may also develop
  • A low level of protein in the blood also tends to allow fluid to seep out of the blood vessels.

A chest X-Ray confirms a pleural effusion. If the cause of the effusion is known then no further tests may be needed. Sometimes a pleural effusion is the first sign of an underlying condition. Further tests may then be advised to find the cause of the effusion. These may include lung tests and taking a sample of the fluid and pleura to examine in the laboratory.


A large pleural effusion, which is causing shortness of breath can be drained. This is usually done by inserting a needle or tube through the chest wall. A local anaesthetic is injected into the skin and chest wall first to make the procedure painless.

A major part of treatment is usually directed to the underlying cause of the effusion. For example, antibiotics for pneumonia, chemotherapy or radiotherapy for cancers, etc.

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