Thoracentesis is a procedure to remove fluid from the space between the lungs and the chest wall called the pleural space.
It is done with a needle (and sometimes a plastic catheter) inserted through the chest wall. This pleural fluid may be sent to a lab to determine what may be causing the fluid to accumulate in the pleural space. Normally only a small amount of pleural fluid is present in the pleural space. Accumulation of excess pleural fluid (pleural effusion) may be caused by many conditions, such as infection, inflammation, heart failure, or cancer. If a large amount of fluid is present, it may be difficult to breathe. Fluid inside the pleural space may be found during a physical examination and is usually confirmed by a chest X-ray.