5. gastric volume assessment (clear fluids)

  • The cross-sectional area of the antrum (CSA) has a linear correlation with the gastric volume
  • To measure the CSA:
    • Identify the antrum at the level of the aorta in the RLD
    • Obtain a still image of the antrum at rest (between peristaltic contractions)
    • Use the free-tracing tool of the ultrasound machine to measure the CSA including the full thickness of the gastric wall (from serosa to serosa)
    • Use a predictive model to assess the gastric volume


  • The following model and related table are applicable to non-pregnant adults for gastric volumes up to 500 mL:

Volume (mL) =27.0 + 14.6 x Right-lat CSA – 1.28 x age



Antral grading system (grades 0 - 2)


  • Most fasted individuals (> 95 %) present a grade 0 or 1 antrum which correlates with low gastric volume
  • A grade 2 antrum is rarely seen in fasted patients and is suggestive of significant gastric volume

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