Gastric Ultrasound

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Basics & Technique - Tummy Peeks

  • Purpose: Evaluate gastric content & volume; predict aspiration risk.
  • Patient Prep: Supine, then Right Lateral Decubitus (RLDP). NPO status.
  • Probe: Curvilinear (low frequency, 2-5 MHz) or phased array.
    • Depth setting: ~10-15 cm.
  • Technique:
    • Sagittal midline view in epigastrium.
    • Identify antrum: between aorta (posterior) & left liver lobe (anterior).
    • Scan in both supine & RLDP.
  • Antral Assessment:
    • Qualitative: Empty (bull's eye), clear fluid (an-/hypoechoic), solids/particulate (hyperechoic).
    • Quantitative: Measure antral cross-sectional area (CSA) in RLDP; correlates with volume.

⭐ Right Lateral Decubitus Position (RLDP) is key for differentiating solid food from contracted empty antrum, and for accurate volume assessment.

Gastric ultrasound sagittal view: probe position & anatomy

Qualitative Grading - Antral Artistry

Qualitative antral assessment guides aspiration risk stratification. Key is the Perlas grading system:

GradeAntral Appearance & ContentsAspiration Risk
0Empty; walls apposed (flat or "bull's eye")Low
1Clear fluid only (anechoic); antrum may be distendedLow*
2Solid food, thick fluids, or particulate matter (hyperechoic)High
  • Clinical Implications:
    • Grade 0-1 (low volume clear fluids): Generally proceed with anesthesia as planned.
    • Grade 2: High risk; consider Rapid Sequence Induction (RSI), delaying surgery, or regional anesthesia.

⭐ Perlas Grade 2 antrum (solid or particulate contents) indicates a high risk of aspiration, often necessitating modification of the anesthetic plan.

Quantitative Measurement - Volume Vibes

  • Measure Antral Cross-Sectional Area (CSA) in Right Lateral Decubitus (RLD).
    • $CSA_{antrum} (cm^2) = (\pi/4) \times AP_{diam} \times CC_{diam}$.
  • Gastric volume (GV) estimation correlates with CSA.
  • Risk Thresholds (Adults):
    • Clear fluids:
      • Low risk: GV <1.5 mL/kg.
      • Consider risk if GV >0.8 mL/kg.
    • High risk: GV >1.5 mL/kg OR any particulate matter. Gastric Antrum CSA and Volume Calculation

⭐ Gastric volume >1.5 mL/kg, or presence of particulate matter, is generally considered high risk for pulmonary aspiration in adults.

Anesthetic Decisions - Go-No-Go Guts

  • POCUS gastric scan: The "Go-No-Go" signal for airway strategy.
  • Qualitative (Perlas grades 0-2) & quantitative (volume estimation) assessment.
  • High-risk findings (Grade 2, solids, high volume) dictate:
    • Deviation from standard NPO.
    • Mandatory Rapid Sequence Intubation (RSI).
    • Potential delay/cancellation of elective procedures.
  • Low-risk (Grade 0-1, empty/clear fluid) allows proceeding with caution.

⭐ Gastric ultrasound findings directly influence decisions on NPO guideline adherence, need for Rapid Sequence Intubation (RSI), or potential case delay/cancellation.

High‑Yield Points - ⚡ Biggest Takeaways

  • Gastric POCUS assesses aspiration risk via gastric content/volume.
  • Key views: Supine and Right Lateral Decubitus (RLD).
  • Use low-frequency curvilinear probe for sagittal antral imaging.
  • Perlas Grade 0: Empty; Grade 1: Fluid in RLD; Grade 2: Fluid in supine & RLD.
  • Differentiates empty, clear fluid, vs. solid/particulate matter.
  • Crucial for RSI decisions and aspiration prophylaxis.
  • Volume > 1.5 mL/kg indicates ↑ risk; qualitative findings often guide.

Practice Questions: Gastric Ultrasound

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