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Thoracentesis is a procedure to remove fluid from the space between the lining of the outside of the lungs (pleura) and the wall of the chest.

A small area of skin on your chest or back is washed with a sterilizing liquid. Some numbing medicine (local anesthetic) is injected in this area.

A needle is placed through the skin of the chest wall into the space around the lungs, called the pleural space. Fluid is collected and may be sent to a laboratory for testing (pleural fluid analysis).

No special preparation is needed before the test. A chest x-ray may be performed before and after the test.

Do not cough, breathe deeply, or move during the test to avoid injury to the lung.

You will sit on a bed or on the edge of a chair or bed. Your head and arms will rest on a table.

The skin around the procedure site is cleaned and the area is draped. A local numbing medicine (anesthetic) is injected into the skin. The thoracentesis needle is inserted above the rib into the pleural space.

You will feel a stinging sensation when the local anesthetic is injected. You may feel pressure when the needle is inserted into the pleural space.

Tell your health care provider if you feel shortness of breath or chest pain.

Normally, very little fluid is in the pleural space. A buildup of too much fluid between the layers of the pleura is called a pleural effusion.

The test is performed to determine the cause of the extra fluid, or to relieve symptoms from the fluid buildup.

Normally the pleural cavity contains only a very small amount of fluid.

Testing the fluid will help your health care provider determine the cause of pleural effusion. Possible causes include:

• Cancer
• Cirrhosis
• Heart failure
• Infection
• Kidney disease

If your health care provider suspects that you have an infection, a culture of the fluid may be done to test for bacteria.

The test may be also performed for the following conditions:

• Asbestos-related pleural effusion
• Collagen vascular disease
• Drug reactions
• Hemothorax
• Pancreatitis
• Pneumonia
• Pulmonary embolism
• Pulmonary veno-occlusive disease
• Thyroid disease

• Bleeding
• Fluid buildup
• Infection
• Pneumothorax
• Pulmonary edema
• Respiratory distress

A chest x-ray is often done after the procedure to detect possible complications.

Pleural fluid aspiration; Pleural tap

Blok B, Ibrado A. Thoracentesis. In: Roberts JR, Hedges JR, eds. Clinical Procedures in Emergency Medicine. 4th ed. Philadelphia, Pa: Saunders Elsevier; 2004:chap 9.

Updated by: Benjamin Medoff, MD, Assistant Professor of Medicine, Harvard Medical School, Pulmonary and Critical Care Unit, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.