Pleural Effusion

The lungs are surrounded by two thin layers of tissue called the pleura, with a small amount of fluid between them that helps the lungs move smoothly as you breathe. A pleural effusion is when too much fluid builds up in this space.

As the fluid increases, it can take up room that the lung needs to expand, which is why a pleural effusion often causes breathlessness. A pleural effusion is not a disease on its own; it is a sign that something else is going on in the body, so finding and treating the cause is an important part of care.

Many people notice shortness of breath, especially when active or lying flat, along with chest discomfort or a sharp chest pain that may be worse when breathing in. A dry cough is also common. A small effusion may cause no symptoms at all and may be found by chance on a scan done for another reason.

If a pleural effusion is caused by an infection, there may also be a fever and feeling generally unwell. Sudden or severe breathlessness should always be assessed urgently.

There are many possible causes, often grouped into two types. Transudative effusions are usually caused by changes in pressure or low protein in the blood, with heart failure being a common reason. Exudative effusions are caused by inflammation, infection, injury, or blockage, such as pneumonia, cancer, a pulmonary embolism, or conditions affecting the liver or kidneys.

Identifying which type is present helps point to the underlying cause, which is why testing a sample of the fluid is often a key step.

A chest X-ray often shows fluid around the lung, and an ultrasound or CT scan can give a clearer picture of how much fluid there is and what might be causing it. Ultrasound is also used to guide procedures safely.

To find the cause, doctors frequently carry out a thoracentesis (also called a pleural tap), in which a thin needle is used to take a sample of the fluid through the chest wall, usually with local anaesthetic. The fluid is then tested for signs of infection, cancer cells, protein levels, and other clues. This same procedure can also remove larger amounts of fluid to ease breathing.

Treatment has two aims: relieving symptoms and treating the underlying cause. If the fluid is making breathing difficult, it can be drained, either with a needle (thoracentesis) or by placing a small tube (a chest drain). Treating the underlying condition, such as heart failure, an infection, or cancer, with the appropriate medicines or therapies is essential to stop the fluid coming back.

If effusions keep returning, particularly with certain conditions, doctors may recommend a procedure such as pleurodesis, which helps seal the pleural space so fluid is less likely to collect, or an indwelling drain that allows fluid to be removed regularly at home. The best approach depends on the cause and your overall health.

Because a pleural effusion is a sign of another condition rather than a disease itself, the outlook depends on the underlying cause and how well it responds to treatment. When the cause is treatable, such as an infection or heart failure that improves with therapy, the effusion often settles.

Most pleural effusions are managed safely, but if fluid is not treated it can sometimes lead to complications such as infection within the fluid (empyema) or thickening of the pleura. Attending follow-up appointments and reporting any return of breathlessness helps keep the condition under control.