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 
How the Test is Performed
  • A small area of skin on your back is cleaned. Numbing medicine (local anesthetic) is injected in this area.
  • A needle is placed through the skin and muscles 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).
How to Prepare for the Test
  • No special preparation is needed before the test. A chest x-ray will be performed before and after the test.
  • Do not cough, breathe deeply, or move during the test to avoid injury to the lung.
How the Test Will Feel
  • 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 pain or pressure when the needle is inserted into the pleural space.
  • Tell your health care provider if you feel shortness of breath or chest pain.
Why the Test is Performed
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.
The test may be also performed for the following conditions:
  • Asbestos-related pleural effusion
  • Collagen vascular disease
  • Drug reactions
  • Hemothorax
  • Lung cancer
  • Pancreatitis
  • Pneumonia
  • Pulmonary embolism
  • Pulmonary veno-occlusive disease
  • Thyroid disease
Normal Results
Normally the pleural cavity contains only a very small amount of fluid.
What Abnormal Results Mean

Testing the fluid will help your health care provider determine the cause of pleural effusion. Possible causes include:
  • Cancer
  • Cirrhosis
  • Heart failure
  • Infection
  • Inflammation
  • Malnutrition
  • 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.
  • Bleeding
  • Infection
  • Pneumothorax
  • Respiratory distress
  • Considerations
A chest x-ray is done after the procedure to detect possible complications.

Source: Medline Plus