A thoracentesis is a procedure that drains fluid or air from the space between the lungs and the wall of the chest (the pleural space). It is done using a hollow needle or a plastic tube inserted through the chest wall. Normally only a small amount of fluid is in the pleural space.

Why thoracentesis is done

A thoracentesis is done to diagnose and treat certain lung problems. It may be done to:

  • collect fluid to look at under a microscope
  • remove excess fluid from the pleural cavity (pleural effusion)
  • remove air that is trapped in the pleural cavity and causing heart and lung problems (tension pneumothorax)

How thoracentesis is done

A thoracentesis can be done in a hospital or outpatient clinic.

Your healthcare team will tell you how to prepare for thoracentesis. Tell your healthcare team about all prescription and non-prescription medicines you are taking.

For thoracentesis, you will sit on the edge of a chair or bed. You will be asked to lean forward and rest your arms on a small table.

After applying a local anesthetic to numb the area where the needle goes in, the doctor makes a small cut and inserts a thin, hollow needle or plastic tube (pleural catheter). To get into the pleural space, this is most often done between the ribs on your back. Sometimes an ultrasound is done to help the doctor find the right place to insert the needle or tube.

Extra fluid is removed through the needle or tube. Once the fluid has been removed, the lungs can expand and take in more air. This makes it easier to breathe.

A small amount of fluid is sent to the laboratory so that it can be looked at under a microscope.

The needle or tube is removed after the fluid has been drained. A small bandage is put over the cut.

If the doctors think that the fluid will build up again, they may put a tunnelled pleural drainage catheter in place. One end of the catheter is put in the pleural space, and the other end is attached to a bottle or container outside of the body. Fluid can be drained at home, without having to keep going back to the hospital.

After thoracentesis, you may have a chest x-ray. This tells doctors how well the pleural space has been drained and can help make sure the lungs have expanded and are working normally.

Thoracentesis usually takes 10 to 15 minutes. It may take a little longer if there is a lot of fluid to remove.

Potential side effects

Side effects can happen with any procedure. They are rare after thoracentesis but may include:

  • discomfort or pain where the needle or tube was put in
  • bruising or bleeding
  • infection
  • collapsed lung

What the results mean

Excess fluid in the pleural space can be caused by many types of cancer, including:

  • lung
  • breast
  • non-Hodgkin lymphoma
  • Hodgkin lymphoma
  • ovarian

Other conditions that can cause excess fluid in the pleural space include:

  • lung infection
  • heart failure (a condition in which the heart doesn’t pump enough blood to the body)
  • kidney (renal) failure
  • liver failure

What happens if a change or abnormality is found

The doctor will decide whether you need further tests, procedures, follow-up care or more treatment.

Special considerations for children

Being prepared for a test or procedure can reduce anxiety, increase cooperation and help the child develop coping skills. Parents and caregivers can help prepare children by explaining to them what will happen, including what they will see, feel, hear, taste or smell during the test.

Preparing a child for a thoracentesis depends on the age and experience of the child. Find out more about helping your child cope with tests and treatments.

Expert review and references

  • British Columbia Ministry of Health . HealthLink BC: Thoracentesis . 2015 :
  • Cope DG . Malignant effusions. Yarbro, CH, Wujcki D, & Holmes Gobel B. (eds.). Cancer Nursing: Principles and Practice. 7th ed. Sudbury, MA: Jones and Bartlett; 2011: 35: pp. 863-878.
  • Lechtzin N . Thoracentesis . Beers MH, Berkow R, (Eds.) . Merck Manual Professional Edition . 2013 :
  • National Heart, Lung and Blood Institute . Thoracentesis . 2012 :
  • University Health Network . Preparing for your Thoracentesis: Information for Patients . 2014 :

Medical disclaimer

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