Thoracentesis is a procedure to remove excess fluid in the space between the lungs and the chest wall. This space is called the pleural space.
Normally, the pleural space is filled with a small amount of fluid—about 4 teaspoons full. Some conditions—such as heart failure, lung infections, and tumors—can cause more fluid to build up. When this happens, it’s called a pleural effusion. A lot of extra fluid can press on the lungs, making it hard to breathe.