Pulmonary contusions from flail chest cause hypoxia primarily because

• A. Pulmonary tissue bruising impairs oxygen diffusion
• B. Blood in the pleural space impairs lung expansion
• C. Air in the pleural space impairs ventilation
• D. Blood clots in the alveoli impair perfusion

Answer: (A)

Pulmonary contusion damages the lung tissue itself, leading to alveolar hemorrhage and interstitial edema that fill and thicken the alveolar–capillary membrane. This directly reduces the surface area available for gas exchange and increases the diffusion distance for oxygen, so less O2 moves from the alveoli into the blood. The result is a drop in arterial oxygen content—hypoxemia—which is the primary reason for hypoxia in this scenario. While other problems like air or blood in the pleural space can contribute to breathing difficulties, they are not the main mechanism here.