Thoracentesis , also known as thoracocentesis (from Greek thōrax 'chest, thorax'—GEN thōrakos—and kentēsis 'pricking, puncture'), pleural tap, needle thoracostomy, or needle decompression (often used term), is an invasive medical procedure to remove fluid or air from the pleural space for diagnostic or therapeutic purposes. A cannula, or hollow needle, is carefully introduced into the thorax, generally after administration of local anesthesia. The procedure was first performed by Morrill Wyman in 1850 and then described by Henry Ingersoll Bowditch in 1852. The recommended location varies depending upon the source. Some sources recommend the midaxillary line, in the eighth, ninth, or tenth intercostal space. Whenever possible, the procedure should be performed under ultrasound guidance, which has shown to reduce complications. Tension pneumothorax is a medical emergency that requires emergent needle decompression before a chest tube is placed. Indications This procedure is indicated when unexplained fluid accumulates in the chest cavity outside the lung. In more than 90% of cases analysis of pleural fluid yields clinically useful information. If a large amount of fluid is present, then this procedure can also be used therapeutically to remove that fluid and improve patient comfort and lung function. The most common causes of pleural effusions are cancer, congestive heart failure, pneumonia, and recent surgery. In countries where tuberculosis is common, this is also a common cause of pleural effusions. When cardiopulmonary status is compromised (i.e. when the fluid or air has its repercussions on the function of heart and lungs), due to air (significant pneumothorax), fluid (pleural fluid) or blood (hemothorax) outside the lung, then this procedure is usually replaced with tube thoracostomy, the placement of a large tube in the pleural space. Contraindications An uncooperative patient or a coagulation disorder that cannot be corrected are relative contraindications. Routine measurement of coagulation profiles is generally not indicated, however; when performed by an experienced operator "hemorrhagic complications are infrequent after ultrasound-guided thoracentesis, and attempting to correct an abnormal INR or platelet level before the procedure is unlikely to confer any benefit". Relative contraindications include cases in which the site of insertion has known bullous emphysema, use of positive end-expiratory pressure (PEEP, see mechanical ventilation) and only one functioning lung (due to diminished reserve). Traditional expert opinion suggests that the aspiration should not exceed 1 L to avoid the possible development of pulmonary edema, but this recommendation is uncertain as the volume removed does not correlate well with