What defines an open chest injury?

An open chest injury is primarily characterized by the presence of puncture wounds that penetrate the chest wall. This type of injury allows external air to enter the thoracic cavity, potentially leading to a collapsed lung (pneumothorax) or other severe complications. The puncture disrupts the integrity of the chest wall and can compromise the respiratory system, making it a critical consideration in emergency first aid.

The other options, while associated with chest injuries, do not specifically define an open injury. Fracture of the rib cage can occur without any external wound, indicating closed injuries. Pain while breathing (pleuritic pain) is a symptom that may arise from various chest injuries, not just from open wounds. Bleeding from the mouth does not directly relate to the presence of an open chest wound, as it can occur from injuries elsewhere, such as in the gastrointestinal system or oral cavity. Therefore, puncture wounds serve as the definitive indicator of an open chest injury.