Your lungs are surrounded by a double layer of membranes called the pleura. In between the two pleural membranes is a narrow space called the pleural space. The pleural space has a small amount of fluid that acts as a lubricant as your lungs breathe in and out.

Thoracentesis (pleural tap) is a medical procedure sometimes used to diagnose or treat certain lung problems. During a thoracentesis, a needle is pushed through your chest wall and into the pleural space, typically to remove excess pleural fluid.

Why would I need thoracentesis?

Thoracentesis is both a diagnostic tool and a treatment. It is mainly used to treat pleural effusion, or the buildup of excess pleural fluid.

Pleural effusion can be dangerous if left untreated. It causes symptoms like:

  • Chest pain.
  • Dry cough.
  • Shortness of breath.
  • Inability to lie flat without pain.

Using thoracentesis to remove some of this excess fluid can help you breathe better.

Pleural effusion is often the result of another disease or condition. Your doctor will use thoracentesis both to treat the pleural effusion and to find the underlying cause.

Among the conditions that can cause pleural effusion:

Complications from surgery or medication. Pleural effusion sometimes happens because of surgery or an allergic reaction to a medication.

Congestive heart failure. Congestive heart failure happens when your heart muscle isn’t able to pump blood efficiently enough to meet your body’s needs. Congestive heart failure is the leading cause of pleural effusion.

Infections. Infections can cause inflammation of the pleura, which causes more pleural fluid to be produced. Sometimes, the fluid drained during a thoracentesis can be sent off to a lab to test for infections.

A specialist can test whether there are bacteria present in the pleural fluid by trying to grow (culture) it from a sample. It can also be tested for viruses or fungi. This can help diagnose infections like:

Liver disease and scarring (cirrhosis). If the liver is damaged, blood pressure in the portal artery (which leads to the liver) increases. Fluid can start to leak out and can move up to the pleural space and may become infected.

Lung cancer. Lung cancer can sometimes lead to pleural effusion. Thoracentesis can treat the symptoms of pleural effusion, and the fluid can also be tested for the presence of cancer cells.

Pancreatitis. Pancreatitis is inflammation of the pancreas, the organ that plays a role in managing your blood sugar level. Sometimes, pancreatitis releases inflammatory chemicals that cause pleural effusion. Thoracentesis can treat this, and the excess pleural fluid may be tested for the inflammatory chemicals.

Pulmonary Embolism. A pulmonary embolism refers to a blood clot in the lung’s blood vessels. This can cause damage, inflammation and pleural effusion.

Systemic lupus erythematosus (lupus). Lupus is a type of autoimmune disorder, meaning your immune system attacks its own healthy tissue, including the pleura. This can lead to swelling and overproduction of pleural fluid.

The thoracentesis procedure

Your experience before, during and after.

Thoracentesis is a safe procedure. Although it usually takes place at a hospital, it is an outpatient procedure, so you will probably go home the same day.

Before the procedure

Before undergoing any procedure, tell your doctor if you

  • Are pregnant.
  • Are taking any medications (like blood thinner) or supplements.
  • Have any allergies (like a latex or medication allergy).
  • Have a bleeding disorder.

Your doctor will tell you about the procedure and describe the risks and benefits. They will also tell you how to prepare for the procedure. This may include having an imaging exam, like a CT scan or chest X-ray. They may also tell you to avoid taking certain medications the night before.

You should also plan to have someone drive you home from the hospital.

During the procedure

The exact method of the thoracentesis will vary depending on why it is being done. Generally, it goes as follows:

  1. You will be asked to remove your shirt and jewelry, and you will be given a hospital gown.
  2. You will sit on the edge of a hospital bed with your arms resting on a table. Or, you may need to lie down on the edge of the bed.
  3. Your doctor will determine the right spot to insert the needle. They may do this by using ultrasound (ultrasound-guided thoracentesis).
  4. Once your doctor has found the right spot, your doctor will inject the area with a local anesthetic to numb the area.
  5. Your doctor will insert the thoracentesis needle in between your ribs. They may use an ultrasound to make sure the needle goes to the right spot. You may feel pressure when the needle is inserted.
  6. Your doctor will slowly drain the excess fluid. If there is a lot of excess fluid, it may be drained in a container connected to the needle by a tube. Your doctor may also tell you to breathe deeply or hold your breath at certain times.
  7. Once the procedure is done, your doctor will remove the needle and apply a bandage.

You will likely have to wait a few hours in the hospital after your procedure. Your doctor may do another chest X-ray to ensure all the fluid was drained and there are no other problems.

If indicated, the fluid will be sent off to a lab for further testing.

After the procedure

After a few hours, you may be told it’s okay for you to go home.

Keep the bandage on for at least 24 hours, and do not take a shower. After 24 hours, you can remove the bandage so long as there is no fluid leaking out.

Call your doctor immediately if you:

  • Develop a fever.
  • Experience redness or swelling at the needle insertion site.
  • Have trouble breathing, shortness of breath or chest pain after your procedure.

Your doctor will call to give you the results of your pleural fluid analysis in a few days. If you have a lung infection or other abnormalities, your doctor may recommend that you return to the hospital.

Thoracentesis: possible complications

Although thoracentesis is a safe and minimally invasive procedure, it does come with some risks. Possible complications of thoracentesis include:

  • Infection at the site of needle insertion.
  • Internal bleeding.
  • Air getting into the pleural space. If this happens, it can lead to a collapsed lung (pneumothorax).
  • Pulmonary edema, or excess fluid inside the lungs. This may happen if too much pleural fluid is removed too quickly.


Radiological Society of North America (RSNA). Thoracentesis for treating pleural effusions (

National Center for Biotechnology Information (NCBI): National Library of Medicine. Thoracentesis (