Tension pneumothorax occurs when air enters the pleural space, either by escaping from damaged lung, tracheobronchial tissue, or from an open chest wound and becomes pressurized during respiration, causing respiratory and circulatory compromise. Patients may have dyspnea, tachycardia, hypotension, distended neck veins, tracheal deviation, and unequal breath sounds. Recognize and treat tension pneumothorax immediately without waiting for radiographs. Immediate needle decompression treatment involves insertion of a 14-gauge, 4.5-cm over-the-needle catheter in the second intercostal space at the midclavicular line (a shorter catheter may not reach the pleural space in many patients). A rush of air through the catheter is confirmatory. Leave the catheter in until a chest tube can be inserted, as the catheter converts the tension pneumothorax to an open pneumothorax.