Guidelines and Recommendations for Performing Gastric Ultrasound
Gastric ultrasound is a valuable point-of-care tool that provides both qualitative and quantitative information about gastric contents, helping clinicians assess aspiration risk before procedures requiring sedation or anesthesia.
Technical Aspects of Gastric Ultrasound
Patient Preparation
- Ensure proper gastric distension by having the patient drink 500 mL of liquid (preferably water) prior to examination 1
- Position the patient in the right lateral decubitus position for optimal visualization of the gastric antrum 2, 3
Equipment and Technique
- Use a low-frequency curved array probe for adequate depth penetration 2
- Perform a standardized scanning protocol focusing on the gastric antrum 3
- Measure both anteroposterior (AP) and craniocaudal (CC) diameters of the gastric antrum 2
- Calculate cross-sectional area (CSA) using the formula: CSA = (AP × CC) π/4 2
- Estimate gastric volume using Perla's formula: GV = 27.0 + 14.6(RLD CSA) - 1.28(age) 2
Clinical Applications and Risk Assessment
Aspiration Risk Assessment
- Gastric ultrasound can reliably differentiate between nil, clear fluid, and thick fluid/solid content 3
- Threshold measurements that predict aspiration risk:
- CC diameter ≥ 2.35 cm (sensitivity 88%, specificity 91%)
- AP diameter ≥ 5.15 cm (sensitivity 88%, specificity 87%)
- Calculated CSA ≥ 9.27 cm² (sensitivity 100%, specificity 87%)
- Gastric volume ≥ 111.6 mL (sensitivity 100%, specificity 92%) 2
High-Risk Patient Populations
- Consider gastric ultrasound assessment in patients with:
- Unknown NPO status
- Urgent or emergent procedures
- Conditions that delay gastric emptying (diabetic gastroparesis, neuromuscular disorders, morbid obesity, advanced hepatic or renal disease) 4
Reliability and Validation
- Gastric ultrasound has "nearly perfect" intrarater and interrater reliability with correlation coefficients >0.8 5
- Both free-tracing and two-diameter methods for measuring antral cross-sectional area are clinically equivalent 5
Integration with Other Diagnostic Modalities
- For gastric cancer assessment, gastric ultrasound should be used in conjunction with other modalities:
- CT with oral and IV contrast remains the primary diagnostic modality for gastric cancer staging 1, 6
- Endoscopic ultrasound (EUS) is recommended for early-stage disease assessment or to determine depth of invasion 1
- PET-CT should be used in combination with EUS and CT for assessment of esophageal and esophago-gastric junctional cancer 1
Limitations and Caveats
- Gastric ultrasound should not replace strict adherence to current fasting guidelines 4
- It should not be used routinely in situations when clinical risk is clearly high or low 4
- The technique requires proper training and experience to achieve reliable results
- Interpretation may be challenging in obese patients or those with altered anatomy
Clinical Decision Making
- Use gastric ultrasound findings to guide clinical decisions about:
- Timing of procedures
- Need for additional precautions during airway management
- Risk mitigation strategies for patients at high risk of aspiration
- Appropriate anesthetic technique selection
By following these guidelines and recommendations, clinicians can effectively use gastric ultrasound as a point-of-care tool to assess gastric content and volume, potentially reducing the risk of aspiration-related complications.