NR 505 Week 6 Measurement and Sampling Write-Up Example

The Measurement Chain Behind "Feeding Intolerance": A Construct, a 60 mL Syringe Read as an Instrument, Residuals 1.5 Times Larger Through a Wider Tube, and a Consecutive Sample for My Unit's Audit

Student Name

College of Nursing, Chamberlain University

NR 505: Advanced Research Methods: Evidence-Based Practice

Instructor Name

Month Day, Year

The Measurement Chain Behind "Feeding Intolerance": A Construct, a 60 mL Syringe Read as an Instrument, Residuals 1.5 Times Larger Through a Wider Tube, and a Consecutive Sample for My Unit's Audit

The Construct, Defined Arguably

The construct at the center of my term question is feeding intolerance: a state in which a patient's gut cannot handle the feeding being delivered, so that continuing would cause harm, whether through vomiting and aspiration or through distension and discomfort. That definition is arguable, and I have written it so. It defines intolerance by consequence, harm from continued feeding, rather than by any single sign. Studies often define it by whatever they happened to measure; Zhang et al. (2026), for example, counted a patient as intolerant after vomiting or any residual above 200 mL, and said they left out distension and diarrhea because other causes could produce them.

Defining the construct first matters because it lets me ask whether an instrument measures it or measures something next to it. Residual volume might measure how much fluid is in the stomach at a given moment. Whether that is the same as intolerance is exactly the question.

The Instrument, and What Its Items Ask

The instrument on my unit is not a questionnaire, but it has items in the same sense: a fixed series of steps, each of which shapes the number that comes out. The nurse stops the pump, attaches a 60 mL syringe to the feeding tube, pulls back until no more fluid comes, records the total, and returns the fluid. Reading the steps closely shows how much the number depends on things other than what is in the stomach.

The first step depends on the tube. A narrow tube collapses under suction or clogs with thick feed, and a tube whose tip lies above the fluid in the stomach draws air. The second depends on the patient's position; the fluid pools in different parts of the stomach when a patient is on their side, on their back or prone. The third, "pull back until no more fluid comes," depends on the nurse's patience and the strength of the pull. None of these steps measures gut function directly. Each measures how much fluid a particular tube, in a particular position, in a particular nurse's hands, could remove.

Reliability With Its Population Attached

The evidence that the number depends on the tube is direct. Metheny et al. (2005) measured residuals in 62 critically ill adults who had both a small-bore 10 French feeding tube and a larger 14 or 18 French sump tube in the stomach at the same time, 645 paired measurements in all. When residuals were over 50 mL, the volumes drawn through the larger tube were about 1.5 times those drawn through the small tube, from the same stomach, minutes apart. Those figures belong to that population: critically ill U.S. adults studied by one research team, with two tubes in place, measured with 60 mL syringes. They cannot be assumed for every tube or every unit, but they show that two measurements of the same stomach can differ by half again because of the tube alone.

Evidence on validity, whether the procedure measures stomach contents at all, comes from children. Valla et al. (2022) examined 64 ventilated, tube-fed children in one French pediatric ICU with bedside ultrasound before and after aspirating residuals. Aspiration reduced the stomach volume, but the stomach was still not empty afterward in 71.9% of the children, and neither the aspirated volume nor the ultrasound volume was associated with vomiting. That is evidence that aspiration underestimates what is in the stomach and that neither measure tracked the sign of intolerance the study used, in that population. I cannot transfer the percentages to adults, but the direction of the finding fits what the adult tube study shows.

Put together, the aspirated residual has weak reliability, since the same stomach gives different numbers through different tubes, and weak validity for the construct, since what it measures is not the same as intolerance. Calling it a validated measure of feeding tolerance, with no population attached, would be wrong.

What My Unit Should Measure Instead

For my unit's project, the outcome I plan to measure is the percentage of prescribed calories delivered, which is better suited to measurement. The construct is nutritional delivery. The instrument is the volume recorded by the feeding pump each 24 hours, divided by the volume prescribed by the dietitian, and the pump's volume counter does not depend on a nurse's pull or a tube's width. Its main weakness is that pumps record what was pumped, not what the patient kept, so a patient who vomits part of a feed will be recorded as receiving it. I will record vomiting separately for that reason.

Who Could Have Been Counted

The sample for the audit will be every ventilated adult on gastric tube feeding admitted to my unit over three months, followed for their first seven days of feeding. Naming who could have been counted, and who will not be, tells a reader more than the final number does.

Four groups will be missed or thinly represented. Patients extubated before 48 hours will usually not reach feeding and will not appear. Patients fed beyond the stomach are excluded, because a gastric residual means something different for them. Patients who die in the first few days will contribute only a few days of data. And because my unit is medical, patients after abdominal surgery, who may have the most feeding intolerance, will not be counted at all. The results will describe medical ICU patients who stay long enough to be fed, which is the population the practice change would affect.

The Method, Named Without Apology

The sampling method is consecutive sampling, a nonprobability method in which every eligible patient in a time window is included. It is not a random sample, and I will not describe it as one. For a unit audit, it is the right method: the goal is to describe the patients my unit actually treats, not to estimate a figure for all ICUs, and including every eligible patient avoids the selection that would come from choosing whom to audit. Its limit is time. Three months in autumn may miss the winter surge in respiratory failure, when the mix of patients changes, and the audit report will say so.

References

Metheny, N. A., Stewart, J., Nuetzel, G., Oliver, D., & Clouse, R. E. (2005). Effect of feeding-tube properties on residual volume measurements in tube-fed patients. Journal of Parenteral and Enteral Nutrition, 29(3), 192-197. https://doi.org/10.1177/0148607105029003192

Valla, F. V., Cercueil, E., Morice, C., Tume, L. N., & Bouvet, L. (2022). Point-of-care gastric ultrasound confirms the inaccuracy of gastric residual volume measurement by aspiration in critically ill children: GastriPed study. Frontiers in Pediatrics, 10, Article 903944. https://doi.org/10.3389/fped.2022.903944

Zhang, H., Chen, Y., Li, F., He, C., Li, X., Wang, Y., Fan, J., Wang, J., Xia, Y., Guo, N., & Yu, K. (2026). Efficacy and tolerability of non-routine gastric residual volume monitoring in mechanically ventilated adults receiving early enteral nutrition: A randomised controlled non-inferiority trial. Nursing in Critical Care, 31(3), Article e70486. https://doi.org/10.1111/nicc.70486