Gastric Ultrasound

Background

Gastric ultrasound is a relatively novel innovation in perioperative ultrasonography. A major concern and source of morbidity and mortality in Anesthesia is the pulmonary aspiration of gastric contents. While it is always recommended to adhere to fasting guidelines, gastric ultrasound may be of utility in non-elective surgery where fasting status is unknown. Additionally, it may prove useful in assessing patients with altered gastric emptying due to medical comorbidities (i.e. diabetes). Gastric ultrasound is non-invasive, relatively easy to perform and can rapidly assess the quantity and type of content in the gastric antrum.

Indication

Questionable or borderline fasting status
- Emergency situations
- Unreliable patients (pediatrics, cognitive dysfunction, language barriers)
Gastric dysmotility (ex. diabetes, opioid use, pregnancy)

Acquisition

Transducer:

Children > 40 kg or adults: curvilinear low frequency
Children < 40 kg: linear high frequency

Patient Position:

Supine
Right lateral decubitus

Operator Mechanics

Operate probe with dominant hand
Place ultrasound machine on same side as operator to manipulate controls with non-dominant hand

Scanning Technique

Begin scan with patient in supine position
Probe is placed on abdomen over the epigastrium with indicator marker directed cephalad
Begin scanning along sagittal plane, fanning from left subcostal margin to right subcostal margin, identifying the gastric antrum
Repeat scan with patient in right lateral decubitus (RLD)

Interpretation

Qualitative

Empty stomach: appears as a “bullseye”
Solid food (early digestive phase): appears as a “frosted glass”
Solid food (late digestive phase)
Liquids
- Clear fluid
- Fluid with air bubbles: appears as “starry night”

Liquid

Solid Food

Quantitative

Gastric antral cross sectional area (CSA)
- Position patient in right lateral decubitus
- Acquire static image of gastric antrum at the level of the aorta
- Using the free-trace function of the ultrasound, measure the CSA (cm2), being sure to include the serosal wall of the stomach
- Using the validated volume model from Perlas et al. (2013), calculate the predicted stomach volume
  - Volume (mL) = 27.0 + (14.6 x RLD CSA) – (1.28 x age)
- Normal fasting volumes are < 1.5 mL/kg
Antral grading system for liquids
- Any solid matter is HIGH RISK

Antral Grading System for Liquids

Adapted from Perlas et al. (2013)

Medical Decision Making

Delay or cancel surgery
Aspiration prophylaxis
Supraglottic device vs. ETT
RSI vs. standard intubation
NG tube
- Pre-induction vs. post
- Prior to extubation

Pitfalls and Modifications

May be unreliable in patients with previous gastric surgery or hiatus hernia
Pediatrics
- Use high frequency probe if weight < 40 kg
- Normal fasting volumes are < 1.1-1.2 mL/kg
- Spencer et al. (2014) pediatric CSA model: Volume = -7.8 + (3.5 X RLD CSA) + (0.127 X age (months))
  - Validated for age 11 months to 17 years old

Comprehension Questions

1. Label the following structures: gastric antrum, liver, pancreas, aorta

2. Which is the optimal probe for gastric ultrasound in adults?

A. Phased array

B. Linear high frequency

C. Curvilinear low frequency

3. What do the following grades represent for qualitative gastric ultrasound

A. Grade 0

B. Grade 1

C. Grade 2

4. Which of the following sonographic appearances correctly corresponds to stomach contents?

A. Starry night

B. Frosted glass

C. Bullseye

5. In a 45 year old, 70 kg patient with a RLD CSA of 7 cm2, what is the predicted gastric volume? Would this patient be considered low risk for aspiration?

Answers

1.

2. C

3.

A. Grade 0 - Empty in supine and RLD

B. Grade 1 - Empty in supine, clear fluid in RLD, volume < 1.5 mL/kg

C. Grade 2 - Clear fluid in supine and RLD, volume > 1.5 mL/kg

4.

A. Starry night - early digestive

B. Frosted glass - fizzy liquids

C. Bullseye - empty

5. Volume = 71.6 mL - low risk, as volume is less than 1.5 mL/kg (105 mL)

References

El-Boghdadly, K., Wojcikiewicz, T., & Perlas, A. (2019). Perioperative Point-of-Care Gastric Ultrasound. BJA Education, 19(7), 219–226. https://doi.org/10.1016/j.bjae.2019.03.003

Perlas, A. (n.d.). Gastric Ultrasound. USRA. Retrieved May 1, 2022, from http://www.usra.ca/regional-anesthesia/specific-blocks/pocus/gastric.php#

Perlas, A., Mitsakakis, N., Liu, L., Cino, M., Haldipur, N., Davis, L., . . . Chan, V. (2013). Validation of a Mathematical Model for Ultrasound Assessment of Gastric Volume by Gastroscopic Examination. Anesthesia & Analgesia, 116(2), 357-363. doi:10.1213/ane.0b013e318274fc19

Spencer, A. O., Walker, A. M., Yeung, A. K., Lardner, D. R., Yee, K., Mulvey, J. M., & Perlas, A. (2014). Ultrasound assessment of gastric volume in the fasted pediatric patient undergoing upper gastrointestinal endoscopy: Development of a predictive model using endoscopically suctioned volumes. Pediatric Anesthesia, 25(3), 301-308. doi:10.1111/pan.12581

Van de Putte, P., Perlas, A., & Bouvet, L., Gastric UltraSound: Home. Gastric Ultrasound. Retrieved May 1, 2022, from https://www.gastricultrasound.org/en/home/