Emergency War Surgery NATO Handbook: Part IV: Regional Wounds and Injuries: Chapter XXVIII: Wounds and Injuries of the Chest

Pneumothorax

United States Department of Defense

The presence of air in the pleural space results in the loss of the normal negative pressure gradient across the alveoli and the visceral pleura. The lung is no longer coupled to the parietal pleura and is collapsed by the recoil of its elastic tissue. Air no longer enters the collapsed alveoli which, however, remain per' fused at least until hypoxiamediated pulmonary vasoconstriction reduces flow. Perfusion of the nonventilated lung tissue results in a ventilationperfusion inequality, which is apparent as desaturation of the arterial blood. The source of the intrapleural air is usually laceration of the pulmonary parenchyma. In a minority of casualties, the lacerated pulmonary tissue forms a flap valve which allows air to enter the pleural space, but not to exit. Intrapleural pressure may become so positive that the mediastinum is displaced to the opposite side and the uninjured lung severely compressed. The dire consequences of a tension pneumothorax are profound alveolar hypoventilation and decreased cardiac output, the latter probably being due to impeded venous return secondary to mechanical kinking of the great veins. Untreated, death may occur within minutes of injury. Pneumothorax may also result from air entering through a hole in the chest wall. Here the problem is not positive intrathoracic pressure, but the fact that, given a sufficiently large hole relative to the area of the airway, there will be less resistance to airflow into the pleural space than into the lung. Profound alveolar hypoventilation results. Open pneumothorax is not commonly seen in living casualties because the trauma necessary to produce a large defect usually causes a fatal intrathoracic injury.

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Operational Medicine 2001

Health Care in Military Settings

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