Thoracentesis (also known as a pleural tap) is a procedure to remove fluid or air from the pleural space. The pleural space is an area between the lung and the chest wall that usually contains just a thin layer of fluid. At times, air or more commonly fluid can collect in this space. If there is enough fluid, a patient can become symptomatic, for example develop shortness of breath. If that occurs, removal can provide relief of these symptoms. Additionally, fluid may need to be removed to help aide in the diagnosis of many conditions. The test is performed as follows: You will sit on the edge of a bed or chair. 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. You will feel a stinging sensation when the local anesthetic is injected. The thoracentesis needle is inserted above the rib into the pleural space and a catheter (small plastic tube) if introduced. You may feel pressure when the needle is inserted into the pleural space. Fluid is collected and will be sent to a laboratory for testing. This procedure has been performed by physicians since 1852!