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A thoracentesis is a procedure in which a hollow needle is inserted through the skin and between the ribs into the space between the lungs and the wall of the chest (pleural cavity). It is used to drain fluid or air from the chest cavity.

Why a thoracentesis is done

A thoracentesis is done to:

  • collect fluid for examination under a microscope
  • remove excess fluid from the pleural cavity (pleural effusionpleural effusionAn abnormal buildup of fluid in the pleural cavity (space between the lungs and the walls of the chest).)
    • The fluid may be examined to help find the cause of the pleural effusion.
    • Removing extra fluid helps a person breathe easier.
  • decompress a tension pneumothorax
    • A tension pneumothorax is a serious condition that develops when air is trapped in the pleural cavity and results in compression of structures in the mediastinum. It can cause problems with heart and lung function. The air is aspirated or removed by inserting a chest tube.

How a thoracentesis is done

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

  • The person often sits on the edge of a chair or bed, leans forward and rests their arms on a small table for the procedure.
  • A local anesthetic is used to numb the area where the thoracentesis needle will be inserted.
  • The doctor then inserts a thin, hollow needle or plastic tube (pleural catheter) through the skin, most often on the person’s back, between the ribs and into the pleural space. Once the needle is inserted, excess fluid is removed.
  • Sometimes an ultrasound is done to help the doctor find the right place to insert the needle or tube for a thoracentesis.
  • A small amount of fluid is sent to the laboratory so that it can be examined under a microscope.
  • More fluid is removed if a pleural effusion is present. (Normally only a small amount of fluid is present in the pleural space). Once the excess fluid is removed, the lungs expand and take in more air, which allows the person to breathe easier.
  • A thoracentesis usually takes 10–15 minutes. It may take a little longer if there is a lot of fluid in the pleural space.
  • The needle or tube is removed once the fluid is drained.
  • If doctors think the fluid will build up again, they may use a tunnelled pleural drainage catheter. One end of this type of catheter stays in place in the body and the other end is attached to a bottle or container outside of the body. The person can drain the fluid at home so they don’t need to keep going back to the hospital.
  • A small bandage is placed on the site where the needle or tube was inserted.
  • A chest x-ray may be done after the procedure to check:
    • how well the pleural space has been drained
    • if the lungs have expanded
    • for any lung problems that may have occurred because of the thoracentesis

Potential side effects

The risks from a thoracentesis are:

  • discomfort or pain at the insertion site
  • bruising or bleeding
  • infection
  • buildup of air in the space between the lungs and the wall of the chest that causes the lung to partially or completely collapse (pneumothorax)

What the results mean

Excess fluid in the pleural space can be caused by:

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

What happens if a change or abnormality is found

The doctor will decide whether further tests, procedures, follow-up care or additional treatment is needed.


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