A 28-year-old man is brought to the trauma bay following a stab wound to the left flank. He is in hemorrhagic shock (BP 78/48, HR 135, RR 32, pale and diaphoretic). Focused abdominal sonography for trauma (FAST) shows free fluid in the peritoneal cavity. Which is the most common source of hemorrhage in penetrating abdominal trauma?

Explanation

## Most Common Bleeding Source in Penetrating Abdominal Trauma **Key Point:** The small bowel and its mesentery are the most frequently injured structures in penetrating abdominal trauma (stab wounds and gunshot wounds), accounting for 30–50% of injuries and being the leading source of hemorrhage in this setting. ### Epidemiology of Penetrating Abdominal Injuries | Structure | Frequency (%) | Hemorrhage Risk | Mortality | | --- | --- | --- | --- | | **Small bowel + mesentery** | 30–50 | High (mesenteric vessels) | 5–10% | | **Liver** | 20–40 | Very high | 10–15% | | **Colon** | 15–25 | Moderate (perforation > bleeding) | 3–5% | | **Stomach** | 10–20 | Low–moderate | 2–4% | | **Spleen** | 10–15 | High | 5–8% | **High-Yield:** In penetrating trauma, the **small bowel is injured more often than any other organ** because: 1. It occupies the largest surface area in the abdomen 2. It is highly mobile and exposed to direct laceration 3. Mesenteric vessel injury causes rapid, life-threatening hemorrhage 4. Most stab wounds follow a linear trajectory through bowel loops ### Why Small Bowel Bleeds Are Most Common in Penetrating Trauma 1. **Anatomical exposure** — small bowel loops fill most of the peritoneal cavity 2. **Mesenteric vasculature** — superior mesenteric artery (SMA) and vein run through the mesentery; injury causes massive hemorrhage 3. **Mechanism** — stab wounds create linear lacerations through multiple bowel loops 4. **Contrast with blunt trauma** — in blunt trauma, solid organs (liver, spleen) are injured; in penetrating trauma, hollow viscera and vessels are at risk ### Clinical Pearl **Penetrating vs. Blunt Trauma:** - **Blunt:** Liver and spleen are most common (solid organ injury) - **Penetrating:** Small bowel and mesentery are most common (hollow viscus + vascular injury) The presence of free fluid on FAST in a hemodynamically unstable patient with penetrating trauma is an indication for **immediate exploratory laparotomy** — do not delay for CT imaging. **Mnemonic: SBM BLEEDS** — **S**mall **B**owel and **M**esentery are the most common sources of hemorrhage in penetrating trauma. [cite:ATLS 10th Edition, Chapter 5: Abdominal and Pelvic Trauma]