Which is a sign of open pneumothorax?

• A. A puncture wound of the chest
• B. Froth or bubbles around the injury
• C. A "sucking" or "hissing" sound when the casualty inhales
• D. Coughing up blood

Answer: (C)

A sucking or hissing sound on inhalation is the defining sign of an open chest injury. When the chest wall has a wound that communicates with the pleural space, air is drawn into the cavity with each breath, producing that audible air-leak sound. This sound signals that air is entering through the wound and is a hallmark of an open pneumothorax, often with the lung on that side partially or fully collapsing.

The wound itself is just the mechanism that allows air to move in, so a puncture wound by itself isn’t the sign. Frothing around the injury or coughing up blood are possible in chest trauma but aren’t the specific indicator of an open pneumothorax; they point to other injuries or complications.