Which finding is most specific for tension pneumothorax?

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Mediastinal shift toward the unaffected side is the finding most specific for tension pneumothorax. When air accumulates under pressure in the pleural space, it not only collapses the ipsilateral lung but also pushes the mediastinal structures, including the heart, away from the affected side. That shift reflects the dangerous pressure physiology of tension pneumothorax and helps distinguish it from a simple pneumothorax, where there isn’t enough pressure to move the mediastinum.

The other signs—hyperresonance on the affected side, decreased fremitus, and diminished breath sounds—can occur with any pneumothorax and indicate air in the pleural space, but they aren’t specific to the tension physiology. Recognizing mediastinal shift is critical because it points to the urgent need for decompression to relieve pressure and improve venous return.