Gastric Ultrasound: How to Rule Out a "Full Stomach" in 5 Minutes
Introduction: Why the "NPO" Rule is No Longer Enough
While the traditional "6 hours for solids, 2 hours for clear liquids" (NPO — nil per os) remains the gold standard, it often fails in the realities of the ICU and emergency surgery. Gastroparesis in diabetes, critical illness, opioid analgesia, or severe stress significantly slow gastric emptying.
Gastric Ultrasound (POCUS) is the only objective bedside tool that allows an anesthesiologist to visualize gastric contents in real-time and prevent Mendelson's syndrome.
Scanning Technique: How to Find the Antrum
Use a convex transducer (or a linear probe for thin patients).
Patient Positioning: Start in the supine position, then move to the Right Lateral Decubitus (RLD). The RLD position is the most sensitive because gravity shifts contents toward the antrum.
Scanning Point: Epigastrium, in the sagittal or parasagittal plane.
Landmarks: * Left lobe of the liver (the antrum is located immediately beneath it).
Pancreas.
Aorta or Superior Mesenteric Artery (deeper).
Ultrasound Findings (Interpretation)
1. Empty Stomach
Appears as a collapsed organ with thick walls, resembling a "target" or "bull’s eye."
2. Clear Fluid
An anechoic (black) zone within the antrum. If fluid is detected, the volume should be calculated using the Perlas scale. Measure the Cross-Sectional Area (CSA) of the antrum from serosa to serosa.
Volume Calculation Formula (Adults):
Critical Threshold: A volume exceeding 1.5 ml/kg is considered a high risk for aspiration.
3. Solid Food
Appears as a heterogeneous mass with echogenic spots (the "starry night" effect). If a patient has just eaten, you will see a hyperechoic arc with acoustic shadowing due to air and food particles.
Clinical Decision Algorithm
| Ultrasound Finding | Aspiration Risk | Recommendation |
| Empty Antrum | Low | Standard Induction |
| Fluid < 1.5 ml/kg | Low | Standard Induction |
| Fluid > 1.5 ml/kg | High | Postpone or RSI |
| Solid Food | Critical | Postpone or RSI with cricoid pressure |
Conclusion for Clinical Practice
Implementing a gastric ultrasound protocol into daily ICU practice is not just a "trend"—it is a vital safety tool. It allows you to avoid unnecessary delays when the stomach is empty or, conversely, to perform Rapid Sequence Induction (RSI) when the risk is life-threatening.
