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The Limitations of Using Gastric Residual Volumes to Monitor Enteral Feedings: A Mathematical Model

Robert Wood Johnson Medical School, Division ofPediatric Surgery, Department of Surgery, New Brunswick, New Jersey

Christopher W. Lentz, MD

University of Missouri Hospitals and Clinics, Division of General Surgery and Critical Care, Department of Surgery, Columbia, Missouri

A variety of methods are used to estimate whether a gastric residual volume is excessive during enteral feedings. In this study, mathematical models of gastric volume during continuous or bolus feedings were developed to evaluate the relevance of measuring residual volumes. The validity of common threshold values of residual volumes that are used to monitor the safety of enteral feeding in infants and adults was tested. A mathematical representation of gastric volume was established using standard integration methods. Assuming an exponential rate of gastric emptying, continuous feedings result in a steady state volume that is proportional to the half-emptying time of the stomach and the rate of addition of endogenous and exogenous fluids. During bolus feedings, a steady state volume will be achieved that is proportional to the volume of the bolus and a rate constant calculated using the half-emptying time and the bolus interval. Based on these models, it can be predicted that threshold values commonly used to monitor feedings do not accurately predict residual volume. In both infants and adults, the threshold values often will overestimate residual volumes at shorter half-emptying times and underestimate residual volumes at longer half-emptying times. Because of the complex relationship between infusion volume, gastric emptying, and gastric volume, evaluation of the volume of gastric contents is an unreliable method for monitoring feeding tolerance.

Nutrition in Clinical Practice, Vol. 16, No. 6, 349-354 (2001)
DOI: 10.1177/088453360101600608


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