This page was reviewed under our medical and editorial policy by

Chukwuemeka Obiora, MD, Surgical Oncologist

This page was reviewed on April 7, 2023.

When fluid builds up in the pleural space (the area between the chest wall and lungs), the care team may perform a thoracentesis to remove the fluid.

What is thoracentesis?

Thoracentesis is a procedure in which the care team extracts excess fluid from the pleural space, which can build up due to a condition called a pleural effusion.

A pleural effusion could make it harder for a patient to breathe. It also may cause pain, dry cough and heaviness in the chest. A thoracentesis may help relieve these symptoms as well as help diagnose why the extra fluid has accumulated in that area.

Pleural effusion and cancer

Cancer patients may need thoracentesis for several reasons.

Patients with certain types of cancer, including lung cancer, 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. Other cancers 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.

Thoracentesis preparation

A few steps may help prepare a patient ahead of a thoracentesis.

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

What to expect during the thoracentesis procedure

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

Thoracentesis position

The patient sits on the edge of a chair or bed with his or her head and arms on a table so the doctor has access to the patient's back, which is the insertion site to reach the pleural space.

Once the patient is in position, the cancer care team cleans the skin near the pleural space and injects medicine to make that area of the skin numb. This is called a local anesthetic. The patient may feel some stinging when this is injected.

Draining fluid from the lungs

Once the anesthesia takes effect, the doctor places a needle through the patient's skin and the muscles of the chest wall to reach the pleural space and removes fluid. The patient may experience some pain or pressure when the needle is placed into the pleural space.

The doctor may ask the patient to breathe out or hold his or her breath during the thoracentesis. Try not to move or cough during the procedure.

Once the fluid is removed, the care team places a bandage over the area.

After thoracentesis

The doctor may send any fluid removed for pleural fluid analysis. The patient also may undergo a chest X-ray right after the thoracentesis to check on his or her lungs.

When the thoracentesis is completed, the care team will briefly monitor the patient's blood pressure and breathing. He or she may return to a regular diet and activities at home, with the doctor’s approval. The care team may advise avoiding heavy physical activity for a couple of days.

Thoracentesis risks and benefits

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

After any procedure, the patient 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 the care team if any of these symptoms occur.

Some risks associated with a thoracentesis include:

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

Speak with the care team about how to help lower these risks.

Thoracentesis fluid results

The care team 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.

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