Use Of Gastric Residual Volumes Research Articles

Should We Stop Using Gastric Residual Volumes?

Early enteral nutrition support is an important component in the management of critically ill patients. However, gastrointestinal tolerance and gastric motility are frequently impaired in this population. Intolerance of enteral nutrition may present clinically as vomiting, aspiration, and abdominal distension. Concerns for the association between gastrointestinal intolerance and the development of ventilator-associated pneumonia have historically led to close monitoring of patients’ tolerance of enteral feeding using various metrics. The measurement of gastric residual volumes (GRV) is the most commonly used surrogate marker for gastrointestinal intolerance in intensive care units. As the name implies, GRV is the volume of enteral formula remaining in a patient’s stomach after cessation of enteral nutrition at various, predetermined time intervals. Despite the logical rationale, there is increasing evidence that monitoring gastric residual volumes may not improve patient outcomes in the critically ill. In this review, we will describe the components of normal gastric motor physiology and review abnormal physiology and dysfunction observed during critical illness. Finally, we will examine the evidence that both supports and refutes the routine use of gastric residual volumes and suggest specific recommendations about the future utilization of this practice.

Nutrition in the intensive care unit

Nutrition has evolved into an integral part of modern critical care for both medical and surgical patients. Multiple international societies now issue evidence-based guidelines to help clinician optimize their patients’ Nutrition. However, adherence to these guidelines throughout the country is poor, and education in nutrition is still lagging in medical school. The authors also highlight four key areas where evidence-based recommendations exist – timing of initiation of enteral feeding, calculating and meeting total daily requirements, use of gastric residual volumes to guide delivery, and interuption of feeding for procedures – but are currently often not followed. Reasons for this lack of adherence are explored, and potential solutions discussed.

Increased threshold for gastric residual volumes and impact on nutrition in the ICU

Gastric residual volumes (GRVs) as measured at regular intervals are considered a marker of tolerance of enteral nutrition (EN). There is controversy surrounding this practice, however. The absolute value for the designated cutoff value for GRVs varies widely in the literature. No prospective randomized control trials have suggested that their use improves patient outcomes in the ICU. It has also not been shown, therefore, that GRVs are an accurate predictor of aspiration or pneumonia. However, the use of GRVs as a guide to the continuation of EN can result in a reduction in the percentage of goal calories received by patients. Prior to February 2013, in our ICU the threshold of GRVs prior to withholding of EN was 200 ml. This tolerated volume was increased to 500 ml in February 2013, in compliance with recent guidelines. By increasing the acceptable GRVs to this level, the aim was to increase the percentage of goal calories received by patients via the enteral route.

Managing gastric residual volumes in the critically ill patient: an update

Gastric residual volumes (GRVs) remain a major deterrent to adequately feeding patients with gastric-delivered enteral nutrition. The purpose of this review was to define the most up-to-date consensus of the utility of the use of GRVs for monitoring tube-feeding intolerance in gastric-fed patients. The paper summarizes the pathophysiology of gastroparesis, the techniques for measuring GRVs, the significance of a large GRV, other factors to consider when measuring GRVs, the correlation between GRVs and aspiration pneumonia, national guideline statements on GRVs, the use of prokinetic agents in the treatment of high GRVs and the clinical impact of tolerating larger GRVs. The utility of GRVs for prevention of aspiration events with tube feeding has been brought into question. Large GRVs usually result from some impediment in gastrointestinal motility (e.g. gastroparesis). There are numerous methods for measuring GRVs, most of which have not been standardized. It appears that there is little correlation between large GRVs and the development of aspiration pneumonia when tube feeding patients. Prokinetic agents have an inconsistent effect on the GRV size. US guidelines state that GRVs of less than 500 ml should not result in termination of enteral feeding. Allowing larger GRVs will allow patients to receive more calories when gastric fed without a deleterious clinical impact. The use of GRVs as a marker of feeding tolerance is of questionable utility.

Gastric Residual Volume (GRV) and Gastric Contents Measurement by Refractometry

Traditional use of gastric residual volumes (GRVs), obtained by aspiration from a nasogastric tube, is inaccurate and cannot differentiate components of the gastric contents (gastric secretion vs delivered formula). The use of refractometry and 3 mathematical equations has been proposed as a method to calculate the formula concentration, GRV, and formula volume. In this paper, we have validated these mathematical equations so that they can be implemented in clinical practice. Each of 16 patients receiving a nasogastric tube had 50 mL of water followed by 100 mL of dietary formula (Osmolite HN, Abbott Laboratories, Columbus, OH) infused into the stomach. After mixing, gastric content was aspirated for the first Brix value (BV) measurement by refractometry. Then, 50 mL of water was infused into the stomach and a second BV was measured. The procedure of infusion of dietary formula (100 mL) and then water (50 mL) was repeated and followed by subsequent BV measurement. The same procedure was performed in an in vitro experiment. Formula concentration, GRV, and formula volume were calculated from the derived mathematical equations. The formula concentrations, GRVs, and formula volumes calculated by using refractometry and the mathematical equations were close to the true values obtained from both in vivo and in vitro validation experiments. Using this method, measurement of the BV of gastric contents is simple, reproducible, and inexpensive. Refractometry and the derived mathematical equations may be used to measure formula concentration, GRV, and formula volume, and also to serve as a tool for monitoring the gastric contents of patients receiving nasogastric feeding.

Enhancing Interpretation of Gastric Residual Volume by Refractometry

The traditional practice of gastric residual volumes (GRVs) is flawed in its design and conception, is poorly standardized in its technique, is an inaccurate measure of gastric emptying, and serves as an insensitive marker for regurgitation and aspiration. The refractive index of a solution (like an enteral formula) is a physical property of that solution, which is remarkably constant and reproducible under varying conditions of concentration, pH, and temperature. Refractometry may be performed quickly and easily at the bedside, requires only a small representative sample of aspirated solution, and provides valuable measurements that can be used to calculate both the true total volume of contents and the specific volume of formula remaining in the stomach. Refractometry complements the use of GRVs as a monitor for patients receiving enteral feeding and should improve the accuracy with which patients at risk for aspiration may be identified.

Monitoring bolus nasogastric tube feeding by the Brix value determination and residual volume measurement of gastric contents

Critically ill patients do not always tolerate nasogastric tube feeding. Gastric residual volumes (GRVs), obtained by aspiration from a nasogastric tube, are widely used to evaluate feeding tolerance and gastric emptying, but controversy exists about what constitutes the true GRV (diet formula or digestive juice) and how it should affect management. In this pilot study, we used the Brix value (BV) measurement of gastric contents to monitor both GRV and food content in patients receiving nasogastric feeding. Forty-three patients receiving bolus nasogastric feeding were monitored for 24 hours before entry into the study and then divided into 2 groups according to traditional use of GRV; patients with low GRVs (< 75 mL) were placed in group 1, whereas patients with higher GRVs (> 75 mL) were placed in group 2. All subjects were given 250 mL of polymeric formula by bolus nasogastric infusion, followed by BV measurement of gastric contents at 0, 30, 60, 120, and 180 minutes. All gastric fluid was aspirated after 180 minutes of feeding; the volume was recorded and BV measurement made, then reinstilled with an added 30 mL of dilutional water, after which a final aspiration and BV measurement was performed. Calculated GRV and volume of formula remaining in the stomach was determined by derived equations. Serial BV measurements decreased in both groups after bolus feeding. For patients in group 2, the decrease was less such that at 180 minutes, the mean BV for gastric contents was significantly higher than for those patients in group 1 (10.1 vs 5.1, respectively; p < .01). Aspirated GRV, calculated GRV, and volume of formula remaining in the stomach at 180 minutes were significantly greater for patients in group 2 compared with those in group 1. Use of refractometry in combination with traditional use of GRV identified 4% (1/25) of patients in group 1 with low GRVs who might have possible gastric dysmotility (> 20% of initial 250-mL volume of formula remaining at 180 minutes) and ensured that 72% (13/18) of patients in group 2 with higher GRVs had sufficient gastric emptying (< 20% of initial 250 mL volume of formula remaining). This pilot study raises the feasibility that refractometry and the BV measurement of gastric juice may be a promising tool for bedside monitoring of tolerance and gastric emptying in patients receiving nasogastric feeding, providing valuable complementary information to traditional use of GRV.

Continuous nasogastric tube feeding: monitoring by combined use of refractometry and traditional gastric residual volumes

Background & aims: Traditional use of gastric residual volumes (GRVs) is insensitive and cannot distinguish retained enteral formula from the large volume of endogenous secretions. We designed this prospective study to determine whether refractometry and Brix value (BV) measurements could be used to monitor gastric emptying and tolerance in patients receiving continuous enteral feeding. Methods: Thirty-six patients on continuous nasogastric tube feeding were divided into two groups; patients with lower GRVs (<75 ml) in Group 1, patients with higher GRVs (>75 ml) in Group 2. Upon entry, all gastric contents were aspirated, the volume was recorded (Asp GRV), BV measurements were made by refractometry, and then the contents were reinstilled but diluted with 30 ml additional water. Finally, a small amount was reaspirated and repeat BV measurements were made. Three hours later, the entire procedure was repeated a second time. The BV ratio, calculated (Cal) GRV, and volume of formula remaining were calculated by derived equations. Results: Mean BV ratios were significantly higher for those patients in Group 2 compared to those in Group 1. All but one of the 22 patients (95%) in Group 1 had a volume of formula remaining in the stomach estimated on both measurements to be less than the hourly infusion rate (all these patients had BV ratios <70%). In contrast, six of the 14 patients in Group 2 (43%) on both measurements were estimated to have volumes of formula remaining that were greater than the hourly infusion rate (all these patients had BV ratios >70%). Three of the Group 2 patients (21%) whose initial measurement showed evidence for retention of formula, improved on repeat follow-up measurement assuring adequate gastric emptying. The remaining five patients from Group 2 (35%) had a volume of formula remaining that was less than the hourly infusion rate on both measurements. The pattern of Asp GRVs and serial pre- and post-dilution BVs failed to differentiate these patients in Group 2 with potential emptying problems from those with sufficient gastric emptying. Conclusions: Refractometry and measurement of the BV may improve the clinical utilization of GRVs, by its ability to identify the component of formula within gastric contents and track changes in that component related to gastric emptying.

Clinical use of gastric residual volumes as a monitor for patients on enteral tube feeding.

The use of gastric residual volumes (GRVs) as a clinical monitor for patients receiving enteral tube feeding (ETF) is based on presumptions that are not physiologically sound and practice that is poorly standardized. This systematic review of the medical literature summarizes results from studies that evaluate the practice, interpretation, and impact on patient outcome from use of GRV. Little data exist to support a correlation of GRV with gastric emptying, volume of gastric contents, or changes in the infusion of ETF. GRVs do not correlate to regurgitation or aspiration, and their use cannot be relied on to protect patients against aspiration pneumonia. Although recent reports suggest that elevated GRVs correlate to "intolerance" of ETF, use as a marker of impending clinical deterioration is limited by the fact that the timing of increases in GRV is unpredictable and high GRVs do not correlate independently to adverse outcome. The practice of GRV may in fact impede delivery of ETF by promoting inappropriate cessation and reducing potential infusion time. Modifying interpretation and the response by healthcare providers to GRV data are needed to preserve any clinical use for this practice.

Amylin is associated with delayed gastric emptying in critically ill children.

Amylin is a novel 37 amino acid that is secreted together with insulin from the pancreas in response to enteral nutrient intake. As a potent inhibitor of gastric motility it plays an important role in the control of carbohydrate absorption. In this study we aimed to determine the relationship between amylin levels and gastric emptying in critically ill children. Prospective interventional study. Tertiary paediatric intensive care unit. Twenty-three patients were studied following admission to a paediatric intensive care unit. The median age (25th-75th centiles) was 5.8 years (1.5-11.6) and weight 20 kg (12.8-47.5). Patients were defined as feed-intolerant on the basis of gastric residual volume greater than 125% 4 h after a feed challenge. Three objective measures of gastric emptying were then calculated from a 6 h paracetamol absorption test. Blood glucose, serum insulin and amylin levels were averaged across the paracetamol absorption test period. Eight patients were classified as feed-intolerant (nTOL) and 15 as feed-tolerant (TOL) [median gastric residual volumes 321% (261-495) and 4% (0-6), respectively]. Gastric emptying was delayed in the feed-intolerant group as assessed by all paracetamol absorption test parameters ( p< or =0.01). The median serum amylin concentration was significantly higher in the feed-intolerant group [nTOL 47.0 (37.7-54.8) versus TOL 22.7 (13.6-26.7) pmol/l, p<0.0001]. A positive correlation between serum amylin and insulin was observed ( r=0.46, p=0.02) but not between amylin and glucose ( r=0.25, p=0.23). The use of gastric residual volumes to define feed intolerance is justified in critically ill children. High serum amylin levels are associated with delayed gastric emptying in these patients. The correlation between serum amylin and insulin levels indicates a degree of preservation of pancreatic hormonal co-release.