This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Surgery
Most serious injury is at 
Select and explain. 
A. open pneumothorax, B. diaphragmatic injury, C. Flail chest, D. Single rib fracture
A: open pneumothorax
Answer: A: open pneumothorax 
Explanation: Answer- A. open pneumothoraxThis is a large open defect in the chest (> 3 cm), leading to equilibration between intrathoracic and atmospheric pressure.Air accumulates in the hemithorax (rather than in the lung) with each inspiration, leading to profound hypoventilation on the affected side and hypoxia.