Thoracentesis refers to the needle aspiration of fluid or air from the pleural space. Although used primarily to determine the cause of pleural fluid accumulation, this procedure helps treat both transudative and exudative pleural effusions by removing accumulated air or fluid that results from injury or such conditions as tuberculosis or cancer. It improves pulmonary function, relieving dyspnea, tachycardia, and other signs. However, unless the underlying cause of the fluid accumulation is identified and corrected, pleural effusion will usually recur. Thoracentesis may also be used to instill medications into the pleural space. An alternative to this procedure for some patients with the malignant pleural effusion is an indwelling cuffed Silastic catheter, which permits patients to undergo palliative treatment on an outpatient basis.