In tension pneumothorax, pleural pressure ipsilateral to the affected lung increases with the accumulation of air in the pleural space. Pressure in the pleural space exceeds atmospheric pressure throughout the entire respiratory cycle, especially during expiration. Associated with the occurrence of a bronchopleural fistula, a persistent air leak into the pleural space that allows air to enter during inspiration but prevents it from exiting during expiration; this mechanism is akin to a one-way valve.
With progression, positive pleural pressure shifts the mediastinum away from the affected lung and toward the contralateral lung, further comprising ventilation and leading to respiratory failure. Progressive mediastinal shift interferes with venous return and leads to reduced cardiac output and, eventually, cardiovascular collapse and death.
Mechanisms of bronchopleural fistula formation include:
- Alveolar rupture (due to barotrauma in mechanically ventilated patients, especially with high tidal volumes, high positive end-expiratory pressure [PEEP] settings, and development of auto PEEP); underlying infection, inflammation, or malignancy; resuscitation efforts
- Injury to the visceral pleura (as with surgery, biopsy, thoracentesis, chest tube placement, central line placement, direct trauma)
- Necrotizing infections (Staphylococcus aureus pneumonia, tuberculosis)