A 28-year-old woman is brought to the trauma center after a stab wound to the left lower chest (5th intercostal space, midaxillary line). She is hemodynamically stable (BP 118/76, HR 92/min), has normal breath sounds bilaterally, and no respiratory distress. Chest X-ray shows a small left-sided pleural effusion but no pneumothorax. Which investigation is most appropriate to exclude hemothorax and guide the decision between observation and tube thoracostomy?

Explanation

## Investigation of Choice for Suspected Hemothorax in Stable Trauma ### Clinical Scenario The patient has a penetrating chest wound with radiographic evidence of pleural effusion but is hemodynamically stable. The goal is to determine whether the effusion is blood (hemothorax) and whether it is large enough to warrant intervention. ### Why FAST (Focused Assessment with Sonography for Trauma) is Correct **Key Point:** FAST of the left hemidiaphragm (also called **ACES** — Assessment of Cardiac, Effusion, Pneumothorax, Hemothorax) is the investigation of choice because it: - **Rapidly detects** free fluid (blood) in the pleural space at the bedside - **Quantifies** hemothorax volume (small vs. large) in real-time - **Guides management:** Small hemothorax (<300 mL) → observation; large hemothorax → tube thoracostomy - **Is non-invasive** and repeatable without radiation - **Is part of ATLS** extended assessment for chest trauma **High-Yield:** In FAST, free pleural fluid appears as an **anechoic (black) stripe** between the visceral and parietal pleura at the left hemidiaphragm. A large hemothorax shows a thick fluid layer (>2 cm) and may compress the left lower lobe. ### Diagnostic Accuracy of FAST for Hemothorax | Investigation | Sensitivity | Specificity | Advantage | | --- | --- | --- | --- | | FAST (ultrasound) | 85–95% | >95% | Bedside, fast, repeatable | | Chest X-ray | 50–70% | >95% | Already done; less sensitive for small effusion | | CT chest | >99% | >99% | Gold standard; not first-line in stable patient | | Diagnostic thoracentesis | 100% | 100% | Invasive; not routine for diagnosis | **Clinical Pearl:** A **small hemothorax** (<300 mL or <2 cm on FAST) in a stable patient can be managed conservatively with observation and serial imaging. A **large hemothorax** (>300 mL or >2 cm) or hemodynamic instability mandates tube thoracostomy (32–40 Fr). ### Why Other Investigations Are Suboptimal **Mnemonic: FAST-HEM** — **F**ree fluid, **A**ir, **S**tability, **T**horacostomy decision; **H**emodynamics, **E**xpectant management, **M**onitoring. [cite:ATLS 10e Student Manual]