## Mechanism of Paradoxical Movement in Flail Chest **Key Point:** Flail chest occurs when three or more consecutive ribs are fractured in two 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 1. **Normal rib cage mechanics**: During inspiration, negative intrathoracic pressure pulls the entire rib cage outward and upward. 2. **Flail segment mechanics**: The flail segment, being disconnected from the rigid rib cage framework, moves paradoxically: - **During inspiration**: Negative intrathoracic pressure acts on the flail segment, but the surrounding intact rib cage moves outward. The flail segment, having lost its mechanical linkage, moves **inward** (toward the mediastinum). - **During expiration**: As intrathoracic pressure becomes positive, the flail segment moves **outward**. ### Clinical Significance **High-Yield:** The primary problem in flail chest is not the paradoxical movement itself but the **underlying pulmonary contusion** and **pain-limited ventilation**, which lead to hypoventilation, atelectasis, and hypoxemia. **Clinical Pearl:** Pain control (epidural analgesia, intercostal nerve blocks) is more important than mechanical stabilization (taping, strapping) because it allows adequate ventilation and cough. ### Management Priorities - Aggressive pain management - Pulmonary hygiene (incentive spirometry, chest physiotherapy) - Early mobilization - Supplemental oxygen and monitoring for hypoxemia - Mechanical ventilation only if respiratory failure develops [cite:ATLS 10th Edition Ch 4]
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