Expansion
A one-way valve traps air, raising intrathoracic pressure and obstructing venous return
Expansion
- A defect in the lung or chest wall acts as a one-way valve: air enters the pleural space on inspiration but cannot leave
- Intrapleural pressure becomes progressively positive
- The ipsilateral lung collapses completely
- The mediastinum shifts away from the affected side
- The shift kinks and compresses the great veins, obstructing venous return
- Cardiac output falls and the patient arrests
The critical point is that death comes from obstructed venous return, not from hypoxia alone, the thin-walled, low-pressure superior and inferior venae cavae collapse long before the aorta would.
Signs are respiratory distress, absent breath sounds and hyperresonance on the affected side, distended neck veins, tracheal deviation away, and hypotension. Treatment is immediate needle decompression followed by a chest drain.