What physical signs indicate flail chest?

Flail chest is characterized by the presence of a segment of the rib cage that is detached from the rest of the thoracic cavity, typically resulting from multiple rib fractures. The most notable physical sign of flail chest is paradoxical chest movement with respiration. This occurs because, during inspiration, the flail segment moves inward instead of outward, and during expiration, it bulges outward rather than collapsing. This abnormal movement of the chest wall can severely impact the effectiveness of ventilation and overall respiratory function, leading to significant respiratory distress.

The other signs mentioned in the options pertain to different conditions. Localized bruising and swelling can occur with various chest injuries but are not specific to flail chest. A persistent cough with green sputum might suggest a respiratory infection rather than flail chest. Increased heart rate with reduced blood pressure could indicate shock or other cardiovascular issues but does not specifically indicate the presence of flail chest. Therefore, the hallmark sign of paradoxical chest movement is key to diagnosing this particular injury and is the primary reason why this choice is correct.