An open pneumothorax occurs when:

• A. Air enters the pleural space from a perforated lung.
• B. Air enters the pleural space from outside the body.
• C. Extreme pleural pressure causes the lung to rupture.
• D. A fractured rib perforates the tissue of the lung.

Answer: (D)

Open pneumothorax happens when there is a chest wall wound that creates a direct opening between the atmosphere and the pleural space. Air can move in and out of the pleural space through that chest wall defect with breathing, which can cause the lung to collapse and may produce a sucking sound at the wound.

That defining feature is why the best description is air entering the pleural space from outside the body via a chest wall opening. If air enters the pleural space through the lung itself or due to extreme pressure changes without a chest wall opening to the outside, it isn’t classified as open pneumothorax.