## Mechanism of Paradoxical Movement in Flail Chest **Key Point:** Flail chest occurs when 3 or more consecutive ribs are fractured in 2 or more places, creating a segment of chest wall that is no longer in continuity with the rest of the rib cage. ### Pathophysiology of Paradoxical Movement During **inspiration**: - Intrathoracic pressure becomes **negative** (becomes more negative than atmospheric pressure) - The intact rib cage expands outward normally - The flail segment, lacking bony continuity, **moves inward** (toward the negative pressure) rather than outward - This is **paradoxical** because it moves opposite to the rest of the chest wall During **expiration**: - Intrathoracic pressure becomes **positive** (less negative) - The intact rib cage recoils inward - The flail segment moves **outward** (away from the positive pressure) **High-Yield:** The paradoxical movement is a direct consequence of the **pressure gradient** across the flail segment, not muscular action or gravity. ### Clinical Significance - Paradoxical movement causes **inefficient ventilation** and **increased work of breathing** - Pain from rib fractures further limits chest wall movement - Risk of **hypoventilation** → atelectasis → hypoxemia → pneumonia - Management focuses on **pain control** (epidural analgesia, intercostal nerve blocks) to allow adequate ventilation **Clinical Pearl:** Positive pressure ventilation (CPAP/PEEP) can act as an internal splint by increasing intrathoracic pressure, reducing the pressure gradient and paradoxical movement. [cite:ATLS 10th Edition Ch 4]
Sign up free to access AI-powered MCQ practice with detailed explanations and adaptive learning.