What characterizes a tension pneumothorax?

A tension pneumothorax is characterized by the build-up of air under pressure within the pleural space. This accumulation of air occurs in such a way that it creates a one-way valve effect, allowing air to enter the pleural cavity during inhalation but preventing it from escaping during exhalation. As a result, the pressure in the pleural space increases and compresses the lung on the affected side, leading to diminished lung function and compromised respiratory effort. This can result in serious complications, including mediastinal shift and cardiovascular instability.

In contrast, a condition where air is trapped allowing both inspiration and expiration does not correspond with the life-threatening nature of tension pneumothorax, as it implies normal ventilation without pressure build-up. Fluid accumulation in the chest without pressure would refer to conditions like a pleural effusion or hemothorax, which differs significantly from a tension pneumothorax. Lastly, inflation of the lungs leading to airway obstruction does not accurately describe tension pneumothorax, as the issue involves air pressure in the pleural space rather than obstruction at the level of the airway. Thus, the defining element of tension pneumothorax is indeed the build-up of air under pressure that compresses the lung.