The space between the lungs and the rib cage is called the pleural space. Normally, there is a small amount of fluid in this space.

Sometimes, excess fluid can accumulate in the pleural space. Doctors refer to this as pleural effusion. It can cause several symptoms, including an inability to breathe properly.

A thoracentesis, also called a pleural tap, is a procedure to remove this fluid.

Read on to find out how a thoracentesis works, how to prepare for the procedure, and the potential risks and complications. We also outline how a thoracentesis differs from other types of drainage procedure.

a doctor with gloves on touching a person's bare back as they prepare for a ThoracentesisShare on Pinterest
A doctor may suggest a thoracentesis to remove fluid from the pleural space.

A thoracentesis is a procedure that involves the use of a needle to remove excess fluid from the pleural space between the lungs and the chest wall.

The medical term for a buildup of fluid in the pleural space is pleural effusion. Some potential causes of pleural effusion include:

Doctors may perform a thoracentesis for one of two reasons:

  • Diagnostic reasons: A thoracentesis can help doctors identify the cause of the pleural effusion.
  • Therapeutic reasons: Too much fluid in the pleural space compresses the lungs, making it difficult for a person to breathe properly. Removing the fluid reduces pressure on the lungs, alleviating pain and shortness of breath.

When preparing a person for a thoracentesis, a doctor may:

  • review all medications that the person is taking and make changes to the types or dosages where appropriate
  • order blood tests to check whether the person’s blood clots normally
  • ask whether the person may be pregnant

A thoracentesis usually takes between 10 and 15 minutes, depending on the amount of fluid in the pleural space. The more fluid there is to drain out, the longer the procedure will take.

Prior to the procedure

Before the procedure, the doctor may perform a chest ultrasound to identify the area with the greatest amount of fluid. Later, the doctor will insert the needle into this space.

Before carrying out the procedure, the doctor will sterilize the injection site and administer a local anesthetic.

During the procedure

People usually remain awake for a thoracentesis. A doctor may ask the person to position themselves sitting on the edge of a chair or bed with their head and arms resting on a table. Sitting in this position helps spread out the spaces between the ribs, making it easier for the doctor to insert the needle into the pleural space.

The doctor may ask the person to hold their breath during the procedure. Some people report the urge to cough as the fluid drains out and their lung re-expands. It is very important to stay as still as possible throughout the procedure to avoid any accidental damage to the lungs.

If there is a lot of fluid to remove from the pleural space, a doctor may attach a tube to the needle to aid drainage. The person may feel a pulling sensation as the fluid leaves their chest.

At the end of the procedure, the doctor will remove the needle and cover the area with a dressing.

After the procedure

A person will receive an X-ray after the thoracentesis to check that the procedure was a success. They will then undergo a period of careful monitoring to ensure that they do not develop complications.

A doctor will send fluid samples to a lab to help identify the cause of the pleural effusion. The results will help the doctor make an accurate diagnosis and provide appropriate treatment.

Most people who undergo a thoracentesis will leave the hospital on the same day as the procedure. Their doctor will provide instructions on how to look after the injection site at home. If necessary, a person can take acetaminophen to alleviate any pain.

People do not usually require sedation for a thoracentesis. However, if a person does receive sedation, they must arrange for someone to accompany them home after the procedure.

Recovery time varies from person to person. People who develop complications will experience a longer recovery period.

According to the National Heart, Lung, and Blood Institute, a thoracentesis can give rise to the following complications:

  • pain
  • bleeding
  • bruising
  • infection
  • air around the lung, called pneumothorax or a collapsed lung

Rarely, a thoracentesis may injure the liver or spleen.

People who undergo a thoracentesis require careful monitoring after the procedure to ensure that they do not develop complications. A healthcare professional will closely monitor the person’s breathing and blood pressure. If the person recovers well, they will be free to go home.

Once home, a person should call their doctor if they develop any of the following symptoms:

A thoracentesis shares similarities with two other types of drainage procedure: a paracentesis and a chest tube insertion. The table below outlines the key similarities and differences between the three procedures.

ProcedureThoracentesisParacentesisChest tube
Procedure typescheduled procedure scheduled proceduretypically an emergency procedure
Location of drainage drains fluid from the pleural space in the chestdrains fluid from the peritoneal cavity in the abdomendrains blood, fluid, or air from around the lungs, heart, or esophagus
Purposeaids breathing and prevents compression of the lungsreduces swelling of the abdomentreats certain medical emergencies
Method of drainage use of a small needle or tube use of a thin, hollow needle or catheter insertion of a tube through a scalpel incision
Duration 15–30 minutes up to 45 minutes tube typically remains in place for several days

A thoracentesis is a relatively simple procedure that involves using a needle to remove fluid from the pleural space. Doctors may use the procedure as a diagnostic tool or as a treatment.

A thoracentesis may cause minor complications, such as pain, bruising, or bleeding at the puncture site. It may also cause more serious complications, such as infection and pneumothorax. Following the procedure, a person will undergo careful monitoring to reduce the risk of complications.

This type of medical procedure is not suitable for everyone. People should discuss their treatment options with their doctor.