This page was reviewed under our medical and editorial policy by

Chukwuemeka Obiora, MD, Surgical Oncologist.

This page was reviewed on April 7, 2023.

A thoracentesis is a procedure that extracts excess fluid from an area called the pleural space, which is located between your chest wall and lungs. The excess fluid is called a pleural effusion. A pleural effusion could make it harder for you to breathe. It also may cause pain, dry cough and heaviness in the chest. A thoracentesis may help relieve these symptoms as well as diagnose why the extra fluid has accumulated in that area.

Why is a thoracentesis performed?

There are several reasons why a doctor may perform a thoracentesis. If you have certain types of cancer, including lung cancer, you have a greater chance of developing fluid around the lungs. About 40 percent of lung cancer patients develop a pleural effusion, according to the American Society of Clinical Oncology. Others associated with a pleural effusion include breast and ovarian cancers, mesothelioma and lymphoma.

It’s also possible for cancer to grow in the pleural space between the chest wall and lungs. When it does, it’s called a malignant pleural effusion.

A thoracentesis is one of several options available to treat a pleural effusion. Other options include a catheter and tube thoracostomy.

How to prepare for a thoracentesis

There are a few ways you can prepare ahead of a thoracentesis.

  • Let your care team know about all medications you use, including over-the-counter drugs and herbal supplements. You may be asked to stop using any medications in advance that make your blood thinner. This includes nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen and naproxen.
  • Alert your care team if you have any allergies to contrast materials, local anesthetic or general anesthesia.
  • If you’re pregnant or think you may be pregnant, let your care team know. Your doctor may want to delay certain tests.
  • Ask if you need someone to drive you home after the procedure.
  • Be prepared to have an imaging test before your thoracentesis. This may be an ultrasound, chest X-ray, computed tomography (CT) scan or fluoroscopy. This type of test shows your doctor where to perform the thoracentesis.

What to expect from a thoracentesis

Your doctor may perform the thoracentesis at a medical office, outpatient center or hospital.

  • You sit on the edge of a chair or bed with your head and arms on a table so your doctor has access to your back, which is the insertion site to reach the pleural space.
  • Next, your cancer care team cleans the skin near the pleural space.
  • You receive medicine to make that area of your skin numb. This is called a local anesthetic. You may feel some stinging when this is injected.
  • Your doctor places a needle through your skin and the muscles of the chest wall to reach the pleural space and removes fluid. You may experience some pain or pressure when the needle is placed into the pleural space.
  • Your doctor may ask you to breathe out or hold your breath during the thoracentesis. Try not to move or cough during the procedure.
  • Once the fluid is removed, your care team places a bandage over the area.

Your doctor may send out any fluid removed for pleural fluid analysis. You also may undergo a chest X-ray right after the thoracentesis to check on your lungs.

When the thoracentesis is completed, your care team will briefly monitor your blood pressure and breathing. You may return to your regular diet and activities at home, with your doctor’s approval. The doctor may ask you to avoid heavy physical activity for a couple of days.

Benefits and risks of a thoracentesis

The benefits of a thoracentesis include helping you breathe better (if the excess fluid is causing breathing problems) and finding the cause of the fluid buildup.

After any procedure, you should monitor for signs of an infection or problems healing at the injection site. This may include a fever of 100.4°F or higher, chest pain, or redness and swelling at the site of injection. Inform your care team if you have any of these symptoms.

Some risks associated with a thoracentesis include:

  • Collapsed lung
  • Bleeding
  • Bruising
  • Infection
  • Liver injury (rare)
  • Spleen injury (rare)

Speak with your doctor about how you can help lower these risks.

Reviewing the results of a thoracentesis

Your doctor may analyze the fluid removed from the thoracentesis, looking for several indicators, including:

  • Cancer cells
  • Blood cells
  • Infection causes, such as bacteria, fungi or viruses
  • Inflammatory markers
  • Levels of glucose, protein or other chemicals

Other causes of pleural effusion include heart failure, liver disease and malnutrition.

The findings of the pleural fluid analysis can help determine what needs to be done to treat it, if anything.

Expert cancer care

is one call away.
appointments in as little as 24 hrs.