In tension pneumothorax, what is the effect on mediastinum and venous return?

• A. Mediastinal shift toward the affected side with increased venous return
• B. Mediastinal shift away from affected side with decreased venous return
• C. No mediastinal shift
• D. Improved venous return

Answer: (B)

In tension pneumothorax, air builds up under high pressure in the pleural space on the affected side, collapsing that lung. The resulting pressure pushes the mediastinal structures away from the injured side. That mediastinal shift compresses the great veins and the heart, reducing venous return to the right atrium (decreased preload) and lowering cardiac output. So the correct idea is that the mediastinum shifts away from the affected side and venous return decreases.