June 2010 Issue

Gastric Residuals — Understand Their Significance to Optimize Care
By Theresa A. Fessler, MS, RD, CNSC
Today’s Dietitian
Vol. 12 No. 5 P. 8

A patient in a medical ICU was receiving a standard enteral nutrition (EN) formula at a rate of 40 mL per hour. The feeding was stopped several times and not advanced to goal over a five-day period due to a measured gastric residual of 80 mL, or twice the flow rate. At that particular hospital, standard nursing practice was to discontinue tube feedings for this reason. Clinical RDs working in hospitals across the country hear similar reports every day.

The problem with using gastric residual volume (GRV) to evaluate EN tolerance is that feedings are often stopped unnecessarily and not advanced to goal, resulting in inadequate nutrition for patients. The practice of checking GRV is based on the belief that high GRVs are a marker of increased risk for regurgitation and aspiration, yet evidence does not exist in the literature correlating GRV with aspiration pneumonia or with ICU or hospital mortality.1

This article will explain how to interpret and gain a better understanding of GRVs and offer strategies to improve EN tolerance when problems occur.

Gastric Physiology
The stomach’s functions include breaking chunks of food into smaller particles and mixing food with gastric acid and digestive enzymes. The stomach is also a reservoir, allowing slow emptying—5 to 15 mL at a time—into the small bowel for continued digestion and absorption. During meal ingestion, the stomach expands to approximately 1,000 mL before pressure in the stomach’s lumen starts to increase.2 Normal gastric emptying occurs within three hours and after a lag time of approximately one hour for a meal of solid foods. The process is slower for high-fat meals. Liquids empty more quickly (within one hour for a glucose solution and two hours for a protein solution).3 During fasting, the stomach secretes approximately 500 to 1,500 mL2; in the fed state, it secretes approximately 2,500 mL per day.3

When interpreting GRV, clinicians must keep in mind that the stomach has reservoir function and that the stomach fluid is a mixture of both the infused EN formula and normal gastric secretions. Chang and colleagues explained this concept in the article “Monitoring Bolus Nasogastric Tube Feeding by the Brix Value Determination and Residual Volume Measurement of Gastric Contents” published in the Journal of Parenteral and Enteral Nutrition (JPEN) in 2004. The Brix value (BV), determined by refractometry, is a measure of the dissolved materials in a solution and is higher for EN formula than gastric secretions. The BV of the stomach contents was lower than that of the EN formula alone immediately after feeding a 250 mL bolus of full-strength polymeric EN formula to patients who were critically ill and on mechanical ventilation. Chang et al also reported that 72% of the patients who had GRVs greater than 75 mL had less than 20% of the initial EN formula bolus remaining in the stomach after three hours.

How High Is Too High?
In a review article, “Measurement of Gastric Residual Volume: State of the Science,” published in 2000 in MEDSURG Nursing, Edwards and Metheny reported that the literature contained a variety of recommendations for what is considered a high GRV, ranging from 100 to 500 mL. Some sources have even (incorrectly) suggested holding tube feedings for a GRV of greater than 30 mL, or 1.5 times the flow rate, or even one half of the hourly flow rate.

In a prospective observational study on gastric residuals during eight hours of continuous EN feeding using an elemental formula, McClave et al found no correlation between GRVs and either objective physical exam or radiographic scores. Fasting volume of the normal stomach ranged from 0 to 98 mL in the study group. The researchers defined high as 100 mL for nasogastric (NG) tubes and 200 mL for gastrostomy (G) tubes and concluded that EN feedings should not be stopped for a single high GRV if there are no other physical examination or radiography findings to show actual gastrointestinal dysfunction. The difference between NG and G tube GRV amounts was based on the thought that NG tubes are more likely to be in the fundus or antrum where fluids are pooled and the G tubes may be higher up along the stomach wall.4

In a prospective observational study published in 2008, Metheny and colleagues did not find a consistent correlation of GRV with aspiration as detected by pepsin in tracheal secretions, but they did find that patients who were categorized as frequent aspirators had a greater incidence of two or more GRVs at or greater than 200 mL and one or more GRVs greater than 250 mL than did the infrequent aspirators.5

Current enteral practice recommendations state that GRV should be checked every four hours during the first 48 hours of gastric feeding and, after that, every six to eight hours for patients who are not critically ill.1 According to current American Society for Parenteral and Enteral Nutrition guidelines for nutrition support in patients who are critically ill, EN should not be stopped for a GRV of less than 500 mL unless there are other signs of feeding intolerance. GRVs ranging from 200 to 500 mL should prompt clinicians to implement methods to reduce aspiration risk.6 Signs of feeding intolerance include emesis, abdominal distention, constipation, and, if the patient is awake and alert, complaints of uncomfortable fullness, abdominal pain, or nausea.

Practical Aspects
There are no standardized methods for checking GRVs. Several factors can affect GRV measurements, such as the type and inner diameter of feeding tubes, the position of the feeding ports in the stomach, and the position of the patient’s body.1 For example, if the end of the tube is near the gastroesophageal junction, it’s less likely fluid will be suctioned out than if the end of the tube is deeper in the body of the stomach where fluid is pooled.1 In a study published in JPEN in 2005, Metheny et al found that of the GRVs that were greater than 50 mL, those taken from larger-diameter (14 and 18 Fr) sump tubes were approximately 1.2 to 1.7 times greater than those taken from smaller-diameter (10 Fr) tubes concurrently in the stomach. Regardless of the lack of standardization of practice, it is worth remembering that there are no data to prove that GRV measurements themselves are clinically meaningful anyway.

When discussing GRVs with other healthcare professionals or patients, it may be helpful to explain fluid volume in visually familiar terms. For example, an EN formula infusing at 60 mL per hour is the same as 4 T per hour, and 150 mL is equal to approximately 5 fl oz, or less than 1 cup. Is it realistic to assume that the stomach cannot or should not hold that much volume?

Feeding Intolerance
Patients at risk for delayed gastric emptying include those with gastroparesis, poorly controlled diabetes mellitus, gastric outlet obstruction, ileus, recent surgery, trauma, or sepsis and those using a large amount of narcotic pain medication. Efforts to prevent aspiration of gastric contents are important in these patients.

Various methods are used to prevent aspiration in patients who are fed enterally. Raising the head of the bed by 30 to 45 degrees to provide upper-body elevation has been shown to reduce aspiration risk.1,6 Physicians can use narcotic antagonists such as naloxone and alvimopan to minimize the slowing effect of narcotics on bowel motility. Prokinetic medications such as metoclopramide and erythromycin can be used when appropriate to stimulate gastric motility. Hyperglycemia can cause delay in gastric emptying, so optimal blood glucose control is important. Postpyloric or jejunal feeding tubes are recommended in situations of delayed gastric emptying or gastric outlet obstruction. Another common practice is to use continuous rather than bolus EN infusion for high-risk patients.1,6 Laxatives or stool softeners to promote bowel regularity and antiemetic medications can also be helpful in promoting EN tolerance. Situations of complete bowel obstruction or prolonged severe ileus would require parenteral nutrition.

Knowledge Into Practice
Many healthcare professionals misunderstand and misuse the common practice of checking GRVs. Knowledge of basic physiology and the scientific literature is necessary to discern the significance of GRVs. Several strategies can be used to help promote tolerance to EN feeding when gastric emptying is too slow.

— Theresa A. Fessler, MS, RD, CNSC, is a nutrition support specialist at the University of Virginia Health System in Charlottesville and a freelance writer.

 

Sidebar
What Is Gastric Residual?
Gastric residual refers to the volume of fluid remaining in the stomach at a point in time during enteral nutrition feeding. Nurses withdraw this fluid via the feeding tube by pulling back on the plunger of a large (usually 60 mL) syringe at intervals typically ranging from four to eight hours. Ideally, most or all of the measured residual fluid should be replaced into the patient’s stomach to prevent fluid, electrolyte, and nutrient loss.

 

References
1. Bankhead R, Boullata J, Brantley S, et al. Monitoring enteral nutrition administration. In: A.S.P.E.N. enteral nutrition practice recommendations. JPEN J Parenter Enteral Nutr. 2009;33(2):122-167.

2. Doherty GM, Way LW. Stomach & duodenum. In: Doherty GM, ed. CURRENT Diagnosis and Treatment: Surgery, 13th edition. McGraw-Hill; 2010.

3. Barrett KE. Gastrointestinal Physiology. McGraw-Hill; 2006.

4. McClave SA, Snider HL, Lowen CC, et al. Use of residual volume as a marker for enteral feeding intolerance: Prospective blinded comparison with physical examination and radiographic findings. JPEN J Parenter Enteral Nutr. 1992;16(2):99-105.

5. Metheney NA, Schallom L, Oliver DA, Clouse RE. Gastric residual volume and aspiration in critically ill patients receiving gastric feedings. Am J Crit Care. 2008;17(6):512-519.

6. McClave SA, Martindale RG, Vanek VW, et al. Guidelines for the provision and assessment of nutrition support therapy in the adult critically ill patient: Society of Critical Care Medicine (SCCM) and American Society for Parenteral and Enteral Nutrition (A.S.P.E.N.). JPEN J Parenter Enteral Nutr. 2009;33(3):277-316.

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