What characterizes a tension pneumothorax?

A tension pneumothorax is characterized by the situation where air enters the pleural cavity but does not have a way to escape. This accumulation of air creates increasing pressure within the pleural space, which can compress the lungs and shift mediastinal structures, potentially leading to severe respiratory distress and cardiovascular compromise. As pressure builds, it can collapse the affected lung and push the heart and major blood vessels to the opposite side of the thorax.

In contrast, the other options do not accurately describe this condition. The idea that air escapes only during expiration does not apply to a tension pneumothorax, as the hallmark involves air being trapped. Similarly, the presence of fluid in the pleural space would suggest a different pathological condition, such as a pleural effusion, rather than a tension pneumothorax. Lastly, while pressure in the pleural cavity does increase in this scenario, it is not accurate to say there is "constant pressure" in the lungs, as the pressures vary based on breathing and the pathological processes at play.