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Pleural effusion

A pleural effusion is a collection of fluid next to the lung. There are various causes. The effusion may cause you to become breathless. The fluid can be drained if necessary. Treatment is mainly aimed at the underlying cause.

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What is a pleural effusion?

Lungs and airways with pleura

Lungs and airways with pleura

A pleural effusion means that there is a build-up of fluid in the space between a lung and the chest wall.

The pleura is a 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 lungs and the chest wall as they move when you breathe.

A pleural effusion develops when this fluid builds up and separates the lung from the chest wall.

Types of pleural effusions

Pleural effusions are classed as transudates or exudates according to how much protein they contain.

  • Transudates have a low protein level of <25g/L. Fluid accumulates due to a disruption in the balance of fluid pressures.

  • Exudates have a high protein level of >35g/L. Fluid accumulates due to increased leakiness (permeability) of the smallest blood vessels.

Transudative pleural effusions

These are most often caused by conditions such as heart failure and liver failure. Less common causes are nephrotic syndrome, hypothyroidism and as a consequence of peritoneal dialysis.

Exudative pleural effusions

The most common causes of these are infections, such as pneumonia or tuberculosis, or cancer. Less common causes include autoimmune conditions such as rheumatoid arthritis, after a heart attack and pancreatitis.

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Causes of a pleural effusion

A pleural effusion is a complication of various conditions. The following are some of the more common causes of a pleural effusion (but there are other rarer causes too):

  • Lung infection (pneumonia), tuberculosis, and 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 and systemic lupus erythematosus (SLE).

  • Heart failure causes 'back pressure' in the veins (blood vessels) 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. For example, cirrhosis of the liver and some kidney diseases may cause a low level of blood protein which allows a pleural effusion to develop.

Symptoms of a pleural effusion

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 you breathe. You may then become breathless.

You may also have symptoms of the condition that is causing the effusion. As a whole range of conditions can cause a pleural effusion, there is a large range of other symptoms that may occur, depending on the underlying cause. One example is you may have a cough and a high temperature (fever) if the cause is lung infection (pneumonia).

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How is a pleural effusion diagnosed?

A chest X-ray usually confirms a build-up of fluid between a lung and the chest wall (pleural effusion). If the cause of the effusion is known then no further tests may be needed. However, 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, blood tests and taking a sample of the fluid and pleura to examine in the laboratory.

Pleural effusion treatment

Treating the underlying cause

A major part of treatment is usually directed to the underlying cause of the build-up of fluid between the lung and the chest wall (pleural effusion). For example, medicines called antibiotics for lung infection (pneumonia), chemotherapy or radiotherapy for cancers, etc.

Therefore, treatment can vary greatly, depending on the cause of the effusion. If the underlying cause can be successfully treated then there is a good chance that the pleural effusion will go away for good. If the underlying cause cannot be treated, or can only be partially treated, the effusion may return if it is cleared (drained).

Treating the effusion itself

Small effusions that cause no symptoms, or only mild symptoms, may just be left and 'observed'. Treatment is usually only needed if the effusion causes symptoms such as breathlessness.

A large pleural effusion that makes you breathless can be drained. This is called a pleural fluid aspiration or pleural tap. It 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. This may be a 'one-off' procedure to relieve symptoms.

Lungs and airways - pleural effusion

Lungs and airways with pleural effusion

However, in many cases, unless the underlying cause can be treated, an effusion is likely to return within a few weeks. Repeated draining of the fluid, when symptoms become troublesome, is one option.

Depending on the underlying cause, other treatment options that are sometimes considered include:


In this procedure, a special chemical (a sclerosant) is injected into the pleural space. This causes inflammation of the pleural membranes and helps them to 'stick' together. This helps to prevent fluid building up again into an effusion. Pleurodesis is most often used in the treatment of repeated (recurrent) effusions caused by cancer.

Talc pleurodesis is often used. If the lung re-inflates after the fluid has been drained, sterile talcum powder (talc) can be used to help stick the pleura together. The doctor puts the talc through the tube attached to the drain and then leaves the drain clamped for about an hour. This allows time for the 2 linings of the lung to stick together. The doctor may attach the drain to a suction machine to apply a small amount of pressure. This can help the pleura to seal together. After a pleurodesis, you will usually have the drain in place for another 24 hours.

Permanent drains

If the effusion is recurrent (perhaps because the underlying cause is not treatable), it is possible to have repeated chest drains put in. This may be uncomfortable and mean spending a lot of time going in and out of the hospital. In this situation, a special catheter called a tunnelled indwelling pleural catheter (TIPC), can be put in. This allows the pleural effusion to be drained easily while you are at home. When you feel you have a build-up of fluid on the lung, the catheter allows the fluid to be drained off into a bottle. This can be done by you, a family member or a nurse. The catheter is inserted in hospital on a day ward. As long as there are no complications, you can usually go home on the same day.

Shunt insertion

An operation to insert a shunt (like an internal drain) to allow the fluid to drain out from the chest into the tummy (abdominal) cavity. This is called a 'pleuroperitoneal shunt'. It is only occasionally used.

Video assisted thorascopic surgery

It may be possible to drain a pleural effusion and do a pleurodesis using a procedure called a thoracoscopy. This is a type of keyhole surgery where the doctor puts a small flexible tube (a thorascope) into the chest. The tube has a light and camera at the end, so the doctors can see into your chest. This is why it is called 'video assisted'. It can be used for taking a biopsy, for draining an effusion or pleurodesis. For this procedure, you lie on your side and are given an injection of a sedative to make you feel drowsy. Local anaesthetic is used to numb the area and the doctor makes a small cut to put the thorascope in. The procedure takes about 40 to 60 minutes and afterwards a chest drain will be left to drain any remaining fluid from the chest cavity.

Surgery also includes an operation to remove the pleura called a pleurectomy. It is sometimes used in people with effusions due to cancer when other treatment options have failed.

Further reading and references

Article history

The information on this page is written and peer reviewed by qualified clinicians.

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