Pleural effusion, sometimes called water on the lung, is a buildup of fluid between the lungs and the chest cavity. It can result from pneumonia, heart failure, cancer, and other conditions.

Pleural effusion, or “water on the lung,” can resemble a respiratory infection. The cause is sometimes respiratory, but there are several other potential causes. A healthcare professional will need to diagnose the underlying cause to provide appropriate treatment.

Symptoms of pleural effusion may include a cough, chest pain, and difficulty breathing.

This article will look at what happens in pleural effusion, why it occurs, and some options for resolving it.

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When a person has pleural effusion, it means that fluid has collected in the space between their lungs and chest cavity, or pleural cavity. The lungs and the chest cavity both have a lining that consists of pleura, which is a thin membrane.

In healthy lungs, these membranes ensure that a small amount of liquid is present between the lungs and chest. This prevents friction as the lungs expand and contract during breathing.

However, someone who has pleural effusion has too much liquid in the pleural space.

Anyone who may have pleural effusion needs immediate medical attention, as it can be life threatening without treatment.

Pleural effusion always results from another condition. Many conditions can cause it. Here are some of the most common causes:

Some medical treatments can also trigger pleural effusion. Examples of these include:

  • open heart surgery or other surgery involving the chest
  • certain medications, including methotrexate, amiodarone, and phenytoin
  • radiation therapy
  • ovarian hyperstimulation

Some people do not experience any symptoms of pleural effusion. If symptoms do occur, they typically start to appear as fluid fills the chest cavity.

Some possible symptoms include:

  • a dry, or unproductive, cough
  • difficulty breathing, especially when lying down
  • fever and flu-like symptoms
  • chest pain
  • sharp, severe pain when taking deep breaths

Persistent hiccups may also be a symptom of pleural effusion.

Some people only find out they have pleural effusion when they undergo a test for another condition.

Also, it is important to note that the symptoms of pleural effusion can resemble those of other lung conditions. A person needs prompt medical help if they experience any of these symptoms.

Below is a 3D model of pleural effusion. It is fully interactive.

Explore the model using your mouse pad or touchscreen to learn more about this condition.

It can be challenging to diagnose pleural effusion, as the symptoms may overlap with those of many other conditions.

To make a diagnosis, a healthcare professional will:

  • ask the person about their symptoms
  • ask them about their overall health and medical history
  • carry out a physical examination
  • suggest imaging tests, such as an X-ray, ultrasound, or CT scan

The healthcare professional will also need to determine whether the effusion is transudate or exudate. The sections below will look at these types in more detail.

Transudate effusion

Transudate effusion usually occurs when another condition causes a pressure imbalance in the blood vessels. As a result, fluid leaks back into the chest. The liquid in the effusion will likely consist of compounds from blood plasma.

Exudate effusion

Exudate effusion usually results from:

  • inflammatory conditions
  • an infection
  • cancer
  • a traumatic injury
  • blocked blood or lymph vessels in the area

A healthcare professional may take a sample of fluid from the pleural space by inserting a needle between the ribs.

These samples can help detect signs of infection, protein levels, and cancer cells. They can also help determine whether the individual has complicated or uncomplicated pleural effusion.

In complicated pleural effusion, signs of inflammation or infection will be present in the fluid. The person may need immediate treatment to prevent potentially serious complications.

In uncomplicated effusion, there will be no sign of infection or inflammation in the fluid. Uncomplicated effusion may be milder and is less likely to result in permanent lung damage.

Some other tests can help identify the cause of the effusion. These include:

  • kidney function tests
  • liver function tests
  • a lung biopsy
  • bronchoscopy
  • a heart ultrasound, to assess for heart failure

These tests help the healthcare professional narrow down the cause of pleural effusion and provide appropriate treatment.

Treatment will depend on the underlying cause. As well as treating the underlying condition, a healthcare professional may need to drain the fluid from the chest.

Chest draining

To drain the chest, the healthcare professional will insert a tube into the pleural space and allow the fluid to leave the body.

They will use local anesthetics to numb the pain where the needle enters the body. This area may be sore once the anesthetics wear off.

They may also need to repeat the process if fluid continues to collect in the pleural space.

There is a small risk of complications associated with chest draining. These include:

  • infection
  • bleeding
  • a collapsed lung
  • fluid entering the lungs

However, these complications are rare.

Other treatments

Other treatments may be necessary in some cases.

In pleurodesis, for example, a surgeon will close the gap between the pleura of the lung and the chest cavity to prevent liquid from building up between them.

In more severe cases, a surgeon can direct fluid from the chest cavity into the abdomen. In some cases, they may also remove part of the pleural lining.

Pleural effusion is a sign of an underlying condition. Both the underlying condition and pleural effusion itself can be life threatening.

The outlook and time needed for recovery will depend on the cause of the effusion, the person’s overall health, and how severe their symptoms are.

The person may need to spend time in the hospital, where they may undergo tests and monitoring. Treatment can often resolve pleural effusion, though it may not always be possible to cure its underlying cause.