Thoracocentesis (pleural aspiration or pleural tap)

Thoracocentesis is a procedure to help symptoms of breathlessness and find the cause of pleural effusion. This is a condition where too much fluid builds up between the lungs and chest wall.

We remove the fluid with a needle from the space between your lungs and chest wall. This is called the pleural space or pleural cavity.

We test the fluid that has been removed to find the cause of the problem. A thoracocentesis can also help your breathing. You can go home on the same day as your procedure.

The procedure is also called a pleural aspiration or pleural tap.

If you have any questions or concerns, please contact your pleural team.

Pleural effusion

The space between your lung and chest wall is called the pleural cavity or pleural space. It is made up of 2 thin layers (membranes). 1 layer lines the lung and the other lines the chest wall.

The 2 layers are close together. They usually have a small amount of fluid in the space between them (about 15 to 30ml).

For some people, a larger amount of fluid can collect in this space (pleural effusion). If you have pleural effusion, the lungs cannot work properly and you will be short of breath.

A thoracocentesis aims to find the cause of pleural effusion. If your doctor knows the cause, it is easier for them to treat the problem.

Before a thoracocentesis

It is important to tell your medical team if you:

  • have had any previous bleeding problems
  • have any allergies to medicines or latex (rubber)
  • take medicines that thin the blood (such as warfarin) 

During a thoracocentesis

The procedure takes place at the hospital. It lasts 10 to 15 minutes.

  • We ask you to remove your clothes on your top half and put on a hospital gown.
  • You get into a comfortable sitting position, leaning forward and resting your arms on a table.
  • You have an ultrasound scan of your back. This is to find the best place to have the thoracocentesis.
  • You have an injection to make the area numb (a local anaesthetic). This might sting slightly for a short time.
  • When the area is numb, we make a small cut.
  • We pass a special needle through this cut and into the pleural space to remove the fluid.
  • When the fluid has been removed, we take out the needle.
  • We put a small dressing on the area where you had the procedure. 

After a thoracocentesis

You might need a chest X-ray after the procedure to check for any lung problems. 

If a large amount of fluid is removed, you might need to stay at the hospital for a short time. This is so that the medical team can check your oxygen levels and breathing.

You can go home on the same day as your procedure.

Call your GP immediately if you have any breathing problems when you are at home.


We send the fluid that has been removed to the laboratory for testing. The results can help your medical team to find the cause of pleural effusion and the best treatment for you.

Risk of a thoracocentesis

A thoracocentesis is a safe procedure. However, as with any procedure, there are some risks.

The risks are usually minor and easily treated.

  • Air collecting in the pleural space (pneumothorax). This usually heals by itself without any treatment. However, a large amount of air might cause the lung to collapse. If this happens, you will need a chest drain. Your medical team talk to you about this.
  • Pain, bleeding, bruising or infection where we put in the needle. This affects fewer than 6 in every 100 people who have a thoracocentesis.
  • Bleeding in or around the lungs. This can happen in rare cases.

We want to involve you in decisions about your care and treatment. If you decide to have a thoracocentesis, we ask you to sign a consent form. This says that you agree to have the treatment and understand what it involves.

If you would like more information about our consent process, please speak to a member of staff caring for you.

Resource number: 4247/VER3
Last reviewed: October 2021
Next review: October 2024

Contact us

If you have any questions or concerns about thoracocentesis, please contact the respiratory medicine department.

Phone 020 7188 5821, Monday to Friday, 9am to 5pm.

Out of hours or in emergency

Please contact your GP or go to your nearest emergency department (A&E).

Do you have any comments or concerns about your care?

Contact our Patient Advice and Liaison Service (PALS)

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