Thoracocentesis (pleural aspiration or pleural tap)

Thoracocentesis is a procedure to help symptoms of breathlessness and find the cause of pleural effusion. 

Fluid is removed using a needle from the space between your lungs and chest wall. This is called the pleural space, or pleural cavity.

The fluid that is removed is tested to see what the cause of the problem is. A thoracocentesis can also help your breathing. 

You can go home the same day of your procedure.

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

Pleural effusion

The space between the lung and the chest wall is known as the pleural cavity, or pleural space.

It is 2 thin layers (membranes). One layer lines the lung, and the other lines the chest wall. These layers lie very close together, and 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 makes it easier for them to treat the problem.

Before a thoracocentesis

Tell your medical team if you:

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

During a thoracocentesis

The procedure will take place at the hospital. It will take 10 to 15 minutes.

  • You will be asked to remove your clothes on your top half, and put on a hospital gown.
  • You will get into a comfortable sitting position, leaning forward and resting your arms on a table.
  • You will have an ultrasound scan of your back, to find the best place to have the thoracocentesis.
  • You will have an injection to numb the area (a local anaesthetic). This might sting slightly for a short time.
  • Once the area is numb, a small cut will be made in the area.
  • A special needle is passed through this cut and into the pleural space to remove the fluid.
  • Once the fluid is removed, the needle is removed.
  • A small dressing will be put on 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 the medical team can check your oxygen levels, and breathing.

You can go home the same day of your procedure.

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


The fluid that has been removed will be sent to the laboratory to be tested. The results can help your medical team work out the cause of pleural effusion, and the best treatment for you.

Risk of a thoracocentesis

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

The risks are usually minor, and are 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 put in. Your medical team will talk to you about this.
  • Pain, bleeding, bruising or infection where the needle was put in. This happens in less than 6 in every 100 people who have a thoracocentesis.
  • Bleeding in or around the lungs can happen in rare cases.

We want to involve you in decisions about your care and treatment. If you decide to go ahead, you will be asked to sign a consent form to say that you agree to have the treatment and you 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, 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).

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Do you have any comments or concerns about your care?

Contact our Patient Advice and Liaison Service (PALS)

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