The lungs are surrounded by the pleural membranes. The visceral pleura directly covers the lung and is separated from the parietal pleura by a layer of surfactant, which reduces friction during respiratory movement. A potential space exists between these two layers, and they may become separated by fluid or air. A lung can collapse to the size of a fist under pressure from either. Standard treatment in the field for an open chest wound is an occlusive dressing. The first thing that can be used to occlude the wound is a gloved hand. After placing the dressing, evaluate the breath sounds and determine if they have improved. The dressing should be taped down on three sides, leaving one side open to relieve the pressure during exhalation (one-way valve). "Burping" the dressing involves lifting one side to make sure any pressure buildup is relieved, as occasionally the dressing can become adhered to the skin, which may lead to a tension pneumothorax. If, after ensuring the occlusive dressing is properly in place, the respiratory rate increases, distress level worsens, oxygen saturations fall and breath sounds decrease, then needle decompression is required. A neurovascular bundle is located underneath each rib, and it is important to avoid damage to that bundle by performing a decompression over the top of a rib. If the patient is intubated before the development of a tension pneumothorax, carefully evaluate the breath sounds (especially if the left-side sounds are diminished) to determine if the ET tube needs to be withdrawn a centimeter. The rescuer performing ventilation will usually recognize a tension pneumothorax by the difficulty in bagging the patient. Remember, when you perform a needle thoracentesis, you are creating an open chest wound. Early signs and symptoms of a tension pneumothorax include diminished or absent breath sounds, severe dyspnea, narrowing pulse pressure, tachycardia and restlessness. Neck veins may be distended, but this can be a normal finding in a supine patient. The classic sign is a deviated trachea; the trachea shifts toward the "good" lung as the buildup of pressure collapses the "bad" lung. This is a late sign and suggests the tension pneumothorax has been developing for some time. One sign that does not normally accompany a plain pneumothorax is hypotension. In this case, the persistent low BP, combined with cool, mottled skin and a delayed capillary refill time, led providers to suspect that a hemothorax was developing as well. With endotracheal intubation and pleural decompression, the positive-pressure ventilations allowed the affected right lung to inflate more fully, utilize more of the available alveolar space and "bag out" some of the blood pooling at the base. The patient's vital signs and saturation improved. He needed surgical treatment and removal of the blood in the pleural space before ventilation and oxygenation could normalize.