A 28-year-old man with a history of gastroesophageal reflux disease (GERD) presents for emergency cesarean section in a pregnant woman (his partner). He is scheduled for RSI but the anesthesiologist wants to confirm gastric volume and pH before proceeding. Which investigation is most appropriate to assess aspiration risk in this patient?

## Assessment of Aspiration Risk Before RSI **Key Point:** Gastric ultrasound (GUS) is the **non-invasive investigation of choice** to assess gastric volume and predict aspiration risk in patients undergoing RSI. ### Gastric Ultrasound: Principle and Application **High-Yield:** Gastric ultrasound measures the **antral cross-sectional area (CSA)** in the supine and right lateral decubitus positions to estimate gastric volume and assess aspiration risk. | Measurement | Interpretation | Clinical Significance | |-------------|-----------------|----------------------| | **Antral CSA (supine)** | <1.5 cm² | Low risk (empty stomach) | | **Antral CSA (supine)** | 1.5–2.5 cm² | Intermediate risk | | **Antral CSA (supine)** | >2.5 cm² | High risk (full stomach) | | **Right lateral decubitus** | Additional assessment | Confirms gastric content; >2 cm² = high risk | ### Why Gastric Ultrasound Is Ideal for RSI 1. **Non-invasive and rapid** — performed in <2 minutes at bedside 2. **Real-time assessment** — visualizes gastric content (fluid vs. solid) and volume 3. **No radiation** — safe in pregnant patients and repeated assessments 4. **Guides RSI decision** — high CSA may prompt: - Modified RSI (cricoid pressure optimization) - Delayed intubation (allow fasting time if not emergent) - Awake intubation in extreme cases 5. **Standardized protocol** — endorsed by ESRA and AAGBI guidelines **Clinical Pearl:** In this patient with GERD, gastric ultrasound is particularly valuable because GERD increases gastric acidity and volume. If CSA >2.5 cm², consider: - Pre-oxygenation with head-up tilt (30°) - Rapid-sequence intubation with optimized cricoid pressure - Increased vigilance for regurgitation - Consideration of H₂-blocker or proton pump inhibitor pre-medication **Mnemonic: GERD + RSI = GUS** — Gastric Ultrasound is mandatory in GERD patients requiring emergency intubation. ## Why Other Investigations Are Not Appropriate **Upper gastrointestinal endoscopy:** Invasive, time-consuming, requires sedation, and delays emergency surgery. Contraindicated in acute settings and does not quantify aspiration risk in real-time. **Gastric pH monitoring via nasogastric tube:** Measures acidity (risk of aspiration pneumonitis) but does NOT assess gastric volume, which is the primary determinant of aspiration risk. Insertion of NGT is uncomfortable and may trigger vomiting in a patient at high aspiration risk. **Barium swallow study:** Anatomical imaging tool for structural pathology (strictures, achalasia), not for assessing acute gastric volume or aspiration risk. Exposes patient to radiation and delays emergency surgery.