During the primary survey of a trauma patient, a hemothorax is suspected. Which is the most common site of bleeding in traumatic hemothorax?

Explanation

## Most Common Source of Traumatic Hemothorax **Key Point:** The lung parenchyma (pulmonary vessels) is the most common source of bleeding in traumatic hemothorax, accounting for the majority of cases. Because pulmonary circulation is a low-pressure system, most of these bleeds are self-limiting and resolve with tube thoracostomy alone. ### Anatomical Basis The lung parenchyma is richly vascularized but operates under low pressure (pulmonary arterial systolic pressure ~25 mmHg vs. systemic ~120 mmHg). Blunt or penetrating chest trauma causes laceration of lung tissue and its accompanying pulmonary vessels. The low-pressure nature of the pulmonary circulation, combined with the tamponade effect of the collapsed lung against the chest wall, allows most parenchymal bleeds to stop spontaneously. ### Comparative Frequency of Bleeding Sources | Source | Frequency | Mechanism | Bleeding Rate | Management | |--------|-----------|-----------|---------------|-------------| | Pulmonary vessels (lung parenchyma) | **Most common** | Lung laceration, contusion | Low pressure, usually self-limited | Tube thoracostomy (>85% definitive) | | Intercostal vessels | Second most common | Rib fracture, direct laceration | Moderate to brisk (systemic pressure) | Tube thoracostomy ± surgical ligation | | Internal mammary vessels | Less common | Anterior chest wall injury | Brisk (systemic pressure) | Often requires surgical intervention | | Mediastinal vessels | Rare | Penetrating injury near hilum/aorta | Massive | Immediate thoracotomy, high mortality | **High-Yield:** Most traumatic hemothoraces (>85%) resolve with tube thoracostomy alone precisely because the predominant source — lung parenchyma — bleeds at low pressure and is tamponaded by the re-expanding lung. This is a classic teaching point in Bailey & Love's Short Practice of Surgery and Schwartz's Principles of Surgery. **Clinical Pearl:** A hemothorax with >1500 mL initial output or ongoing bleeding >200 mL/hr after tube placement suggests a higher-pressure source (intercostal, internal mammary, or mediastinal vessels) and warrants surgical exploration — these are the minority of cases. **Why intercostal vessels are NOT the most common:** Although intercostal vessel injury is frequently cited in the context of rib fractures, the sheer volume of lung parenchyma exposed to trauma and the frequency of pulmonary contusion/laceration make parenchymal bleeding the statistically predominant source. Intercostal vessel bleeding, while dramatic, is less frequent overall. **Reference:** Schwartz's Principles of Surgery, 11th ed.; Bailey & Love's Short Practice of Surgery, 27th ed.; ATLS 10th edition — all identify lung parenchyma as the most common bleeding source in traumatic hemothorax.