In what scenario does subcutaneous emphysema occur?

Subcutaneous emphysema occurs when gas escapes from the lungs into the surrounding tissue, typically as a result of a rupture in the respiratory tract. This condition is often seen in scenarios involving trauma or barotrauma, where a sudden pressure change can cause air to be pushed into the soft tissues surrounding the neck. When gas gets trapped in the subcutaneous layer, it can lead to swelling and a characteristic crackling sensation upon palpation. This is particularly relevant for divers, as the pressure differences they experience can exacerbate such injuries, especially if there is a pre-existing condition or injury that compromises the integrity of the lung tissue.

In the context of diving, this phenomenon is crucial to understand for safety reasons, as it indicates a possible serious underlying problem that requires prompt medical attention. The other scenarios listed, while potentially hazardous in a diving context, do not directly lead to the escape of gas from the lungs into the tissues as subcutaneous emphysema does.