Why is a gastric residual volume of 200ml used as a threshold for holding feeding?

Gastric Residual Volume of 200ml as a Threshold for Holding Feeding

The 200ml gastric residual volume (GRV) threshold for holding enteral feeding is largely arbitrary and not well supported by evidence, as studies have not consistently confirmed a relationship between GRVs and outcomes such as aspiration pneumonia. 1

Evidence Behind the 200ml Threshold

The 200ml threshold appears to be based on historical practice rather than robust scientific evidence. The Surviving Sepsis Campaign guidelines specifically address this issue:

• The guidelines suggest against routinely monitoring GRVs in critically ill patients with sepsis or septic shock (weak recommendation, low quality of evidence) 1
• However, they do suggest measurement of gastric residuals in patients with:
  • Demonstrated feeding intolerance (e.g., vomiting, reflux of feeds)
  • Those considered at high risk for aspiration (e.g., surgical patients, hemodynamically unstable patients) 1

Scientific Rationale and Limitations

Physiological Considerations

• Normal postprandial stomachs can accommodate volumes much higher than 200ml 2
• Computer simulation models show that gastric residual volumes can reach a plateau of 225-900ml between 3-13 hours after starting formula delivery at normal gastric emptying rates of 20-50% per hour 2
• Gastric emptying half-life of water is approximately 15 minutes, while caloric beverages empty much slower 3

Evidence Against Low GRV Thresholds

• A multicenter non-inferiority trial of 452 critically ill patients found that not monitoring GRVs was non-inferior to monitoring GRVs at 6-hour intervals regarding the primary outcome of ventilator-associated pneumonia 1
• Poor correlation exists between GRV measurements and aspiration risk 4
• Sensitivities for detecting aspiration at various GRV thresholds are extremely poor:
  • 400ml = 1.5% sensitivity
  • 300ml = 2.3% sensitivity
  • 200ml = 3.0% sensitivity
  • 150ml = 4.5% sensitivity 4

Current Practice vs. Evidence

Despite the evidence suggesting higher thresholds are safe:

• A 2012 survey found that 89% of nurses terminated tube feeding at volumes <300ml and only 3% allowed volumes >400ml 5
• The primary concerns cited were risk of aspiration (90%), feeding intolerance (81%), and risk of regurgitation (67%) 5

Recommendations for Practice

Based on the most recent evidence:

1. For non-surgical critically ill patients:

   • Consider higher GRV thresholds (400-500ml) or not monitoring GRVs at all 1
   • Focus instead on clinical signs of intolerance like vomiting or reflux of feeds

2. For surgical or high-risk patients:

   • More conservative approach may be warranted
   • One observational study found increased aspiration risk in surgical patients when GRV >200ml was registered more than once 6

3. When GRV exceeds threshold:

   • Consider prokinetic agents rather than immediately holding feeds 1
   • Post-pyloric feeding tube placement may be beneficial for patients with persistent high GRVs 1

Practical Approach to Managing High GRVs

1. Assess for other signs of feeding intolerance (abdominal distension, vomiting)
2. Consider patient positioning (head of bed elevated at least 30°) 1
3. Try prokinetic agents before holding feeds 1
4. For persistent high GRVs, consider post-pyloric feeding 1

The practice of using 200ml as a threshold appears to be more based on tradition than evidence, with current guidelines suggesting higher thresholds or abandoning routine GRV monitoring altogether in most critically ill patients.