Gastric Ultrasound

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.

Qualitative Grading - Antral Artistry

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

• 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 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.