Background: During tube feeding, it is a common practice to check gastric residual volume frequently for indications of pathologic impairment of gastric emptying. The volume threshold standards for holding feedings are applied nonselectively, disregarding slowing of gastric emptying by nutrient-triggered intestinogastric inhibitory feedback. We developed a computer simulation model considering this feedback to test the hypothesis that gastric residual volume increases with slower gastric emptying and faster formula delivery but reaches a plateau volume (equilibrium between input and output) at volumes commonly seen in the postprandial stomach.
Methods: A computer simulation model using Microsoft Excel 4.0 calculated the cumulative gastric residual volume over time when the input volume into the stomach is 125 mL/h (endogenous secretions)+ 0 to 125 mL/h (formula delivery rate) and the output volume out of the stomach is equal to gastric emptying rates that varied between 0% and 50%/h. The model simulated nasogastric feeding with nine different rates of gastric emptying and six different rates of formula delivery. Measurements consisted of the cumulative gastric residual volume at the end of each hour for a minimum of 48 hours.
Results: (1) Gastric residual volumes 1.5 to 6 times the commonly applied "stop feeding" threshold volume of 150 mL are encountered at gastric emptying rates of 20% to 50%/h; (2) gastric residual volume stabilizes to a plateau of 225 to 900 mL between 3 and 13 hours after start of formula delivery at these rates; and (3) at 0% gastric emptying, gastric residual volume does not reach a plateau.
Conclusions: At gastric emptying rates expected with nutrient-triggered inhibitory feedback and at formula delivery rates common in nutrition support, gastric residual volume reaches a plateau rapidly and at volumes commonly encountered in normal postprandial stomachs. On the basis of the results of this model, the current practice of stopping enteral feeding when gastric residual volume exceeds an arbitrarily selected volume threshold may not be physiologically sound. Clinical studies are needed to verify this model.