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Pneumothorax is air in the otherwise “virtual space” between the parietal and visceral pleurae. The volume and pressure of the air in this space determine the clinical effect, which can range from asymptomatic to life‐threatening. Early signs and symptoms may be subtle and the condition is often not expected. It is therefore important for EMS clinicians to maintain a high index of suspicion for pneumothorax in a variety of presenting complaints and to be aware of potential predisposing or associated conditions (Box 6.3).

Patients may present with pleuritic pain, sudden onset of a sharp pain, minimal to severe shortness of breath, and hypoxemia. Physical exam findings that should prompt consideration of pneumothorax include decreased or absent unilateral breath sounds, subcutaneous emphysema, or evidence of thoracic trauma. Pulse oximetry may or may not decrease depending on the size of the pneumothorax and the underlying pulmonary function and comorbidities of the individual patient. Similarly, EtCO₂ may or may not appreciably change and its interpretation may be further complicated by compensatory hyperventilation or other comorbid conditions. A potentially more sensitive indicator in patients already receiving mechanical ventilation may be decreases in tidal volumes and increases in peak pressures. Ultrasound, if available, can also be used to identify pneumothorax.

The one case that must be recognized clinically is a tension pneumothorax. This occurs when the intrathoracic pressure is so great that ventilation and venous return to the heart are obstructed, leading to respiratory compromise and shock. Besides unilateral decreased or absent breath sounds and subcutaneous emphysema, tracheal deviation and jugular venous distension may be present, but these should not be relied upon. Tension physiology must be recognized and treated immediately.

Tension pneumothorax must be treated immediately with needle thoracostomy (needle decompression). Following skin cleansing, a large‐bore intravenous catheter (14 gauge or larger) should be inserted through the chest wall. When the needle enters the pleural space, a rush of air is often heard. The needle is then removed, leaving the catheter in place. Patients may require decompression with several needle thoracostomies in the prehospital environment as air reaccumulates in the pleural space. Needle decompression traditionally was performed in the second intercostal space at the mid‐clavicular line. Increasing evidence has shown that use of this site is prone to great vessel injury and failure to reach the pleural space [12–14]. Therefore, the Committee on Trauma of the American College of Surgeons now recommends using the fourth or fifth intercostal space between the anterior and mid‐axillary lines [15]. The chest wall should never be penetrated inferior to the nipple line due to risk of splenic or hepatic puncture. Treatment failure is typically due to using too short a needle or the catheter becoming occluded, which requires placement of additional needle(s). The hub of the catheter should either be left open or attached to a Heimlich (one‐way) valve.