Gastric UltraSound

IMAGE ACQUISITION

1. SCANNING TECHNIQUE

  • Abdominal settings
  • Transducer: 
    • Children > 30 Kg or Adults: curved array low-frequency (2-5 mHz)
    • Children < 30 Kg: linear high-frequency (5-12 mHz) – see pediatrics
  • Scan the epigastrium in a sagittal plane 
  • Sweep the transducer from the left to the right subcostal margins
  • Identify the gastric antrum – see applied anatomy
  • Patient position:
    • Start in the supine position
    • Follow with the right lateral decubitus (RLD). Never call an empty stomach based on the supine position

2. applied anatomy

Blue line: scanning plane; A: antrum; Ao: aorta; L: liver; P: pancreas; Sma: superior mesenteric artery

Blue line: scanning plane; A: antrum; Ao: aorta; L: liver; P: pancreas; Sma: superior mesenteric artery

A: antrum; Ao: aorta; C: colon; L: liver; P: pancreas; SI: small intestine; Sma: superior mesenteric artery; Smv: superior mesenteric vein; Sp: spine

A: antrum; Ao: aorta; C: colon; L: liver; P: pancreas; SI: small intestine; Sma: superior mesenteric artery; Smv: superior mesenteric vein; Sp: spine

The gastric antrum:

  • Is the most amenable to sonographic examination 
  • Accurately reflects the content of the entire stomach
  • Hollow viscus with a prominent multi-layer wall
  • Between the liver (anteriorly) and the pancreas (posteriorly)
  • Points de repère importants :
    • Left lobe of the liver
    • Pancreas
    • Aorta
  • Is usually located superficially (3-4 cm)

 

3. GASTRIC WALL

1: serosa; 2: muscularis propriae; 3: submucosa; 4: muscularis mucosa; 5: mucusal air interface

1: serosa; 2: muscularis propriae; 3: submucosa; 4: muscularis mucosa; 5: mucusal air interface

Ao: aorta; C: colon; L: liver; yellow arrows: prominent wall of antrum.

Ao: aorta; C: colon; L: liver; yellow arrows: prominent wall of antrum.

  • Characteristic five-layered wall 
  • Sets the organ apart from other hollow viscus
  • The gastric wall layers are best appreciated with a high-frequency transducer in the fasting state

4. TYPE OF GASTRIC CONTENT

A: antrum; Ao: aorta; D: diaphragm;  L: liver; P: pancreas; R: rectus abdominis muscle; Sma: superior mesenteric artery

  • The antrum has no appreciable content in both supine and RLD (Grade 0 antrum)
  • It appears flat and collapsed or with a round-to-ovoid shape (“bull’s eye” or “target” pattern)

4.1 EMPTY STOMACH

A: antrum; Ao: aorta; D: diaphragm; L: liver; P: pancreas; R: rectus abdominis muscle; Sma: superior mesenteric artery
A: antrum; Ao: aorta; D: diaphragm;  L: liver; P: pancreas; R: rectus abdominis muscle; Sma: superior mesenteric artery

  • The antrum has no appreciable content in both supine and RLD (Grade 0 antrum)
  • It appears flat and collapsed or with a round-to-ovoid shape (“bull’s eye” or “target” pattern)

4.2 SOLID EARLY STAGE

A: antrum; Ao: aorta; L: liver; R: rectus abdominis muscle
A: antrum; Ao: aorta; L: liver; R: rectus abdominis muscle

  • The antrum appears distended with thin walls
  • The content is of high or mixed echogenicity
  • Specific patterns: 
    • “Frosted-glass” pattern (usually shortly after a solid meal). It is due to a mix of air and solid along the anterior wall, blurring the posterior wall and deeper structures

4.3 SOLID LATE STAGE

A: antrum; Ao: aorta; L: liver; P: pancreas; R: Rectus Abdominis muscle; S: spine; Sma: superior mesenteric artery
A: antrum; Ao: aorta; L: liver;  P: pancreas; R: rectus abdominis muscle; S: spine; Sma: superior mesenteric artery

  • Heterogeneous, particulate content (usually after 1-2 hours following a solid meal)
  • Homogeneous, hyperechoic content: characteristic of dairy products or particulate fluids
  • Milk curdles can have a typical biphasic (hyperechoic/hypoechoic) appearance (see additional material)

4.4 CLEAR FLUID

A: antrum; Ao: aorta; D: diaphragm; L: liver; P: pancreas; R: rectus abdominis muscle; S: spine; Sma: superior mesenteric artery
A: antrum; Ao: aorta; D: diaphragm; L: liver; P: pancreas; R: rectus abdominis muscle; S: spine; Sma: superior mesenteric artery

  • The antrum is round and distended with thin walls
  • The content appears anechoic or hypoechoic
  • The size of the antrum is proportional to the gastric volume
  • The antrum will appear larger in the RLD compared to the supine position
  • A volume assessment can differentiate a low (normal) quantity of baseline gastric secretions from a higher (non-fasting) volume 

4.5 FLUID WITH AIR BUBBLES

A: antrum; Ao: aorta; L: liver; P: pancreas; R: rectus abdominis muscle; S: spine; Sma: superior mesenteric artery
A: antrum; Ao: aorta; L: liver; P: pancreas; R: rectus abdominis muscle; S: spine; Sma: superior mesenteric artery

  • Special pattern:
    • “Starry night” (multiple air bubbles on a hypoechoic background) usually seen shortly after ingestion of clear fluids or effervescent drinks
  • A volume assessment can differentiate a low (normal) quantity of baseline gastric secretions from a higher (non-fasting) volume 
Click for more clips

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

  • La siguiente técnica y la tabla asociada hace referencia a adultos (no embarazadas) para volúmenes gástricos de hasta 500 mL:

VOLUME (ML) = 27.0 + 14.6 X DLD-CSA – 1.28 X EDAD

HOW TO MEASURE GASTRIC VOLUME-KNOBOLOGY


Coming soon

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
  • This antral grading system has been validated in children, obese and non-obese adults and obstetric patients
Gastric UltraSound