## Most Common Non-Infectious ARDS Cause in Trauma **Key Point:** Pulmonary contusion is the most frequent direct pulmonary injury leading to ARDS in trauma patients, occurring in up to 75% of blunt chest trauma cases with rib fractures. ### ARDS Causes in Trauma Patients | Cause | Frequency in Trauma | Mechanism | |-------|-------------------|----------| | **Pulmonary contusion** | 40–50% of ARDS cases | Direct parenchymal injury from blunt force | | Fat embolism syndrome | 5–10% | Long bone fractures, especially femur | | Aspiration | 10–15% | Altered mental status, intubation | | Acute pancreatitis | <5% | Blunt abdominal trauma | | Sepsis (secondary) | 30–40% | Infection from wounds, aspiration | **High-Yield:** Pulmonary contusion causes direct alveolar injury with hemorrhage and edema, leading to surfactant loss and ventilation–perfusion mismatch. It is the single most common *direct* pulmonary cause of ARDS in polytrauma. ### Pathophysiology of Pulmonary Contusion 1. Blunt chest wall trauma → parenchymal disruption 2. Alveolar hemorrhage and interstitial edema 3. Surfactant inactivation by blood and inflammatory mediators 4. Neutrophil infiltration and capillary leak 5. Progressive hypoxemia over 24–72 hours 6. Peak injury typically occurs 24–48 hours post-injury **Clinical Pearl:** Pulmonary contusion may not be immediately apparent on initial chest X-ray; infiltrates often worsen over the first 48 hours. CT chest is more sensitive for early detection. **Mnemonic:** **ARDS in Trauma = PFC** - **P**ulmonary contusion (most common direct injury) - **F**at embolism (long bone fractures) - **C**omplications (aspiration, sepsis) **Warning:** Fat embolism syndrome (FES) is often cited in textbooks but occurs in only 5–10% of trauma-related ARDS cases. Pulmonary contusion is far more frequent. Do not confuse the textbook emphasis on FES with its actual epidemiology. [cite:Harrison 21e Ch 297]
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