Use of the refractometer as a tool to monitor dietary formula concentration in gastric juice

Background and Aims: Critically ill patients do not always tolerate nasogastric tube feeding. Gastric residual volumes are widely used to evaluate feeding tolerance, but controversy exists about what constitutes the residual volume (diet formula or digestive juice). In this paper, we describe the use of the refractometer as a tool to monitor dietary formula concentration in gastric juice and evaluate gastric juice refractometry as a possible clinical application. Methods: Brix value (an index of the total solutes in solution) readings for polymeric diet at pH 1, 4,7 and 8, and at 4degreesC, 25degreesC and 37degreesC, and in fasting gastric juice were determined with a refractometer. Results: We found that distilled water, minerals, and vitamins had low Brix values of 0+/-0, 1.2+/-0.1, and 0.4+/-0.1, respectively. On the other hand, because carbohydrate (17 g/100 ml), protein (5.3 g/100 ml), fat (4.1 g/100 ml), and full-strength polymeric diet had high concentrations of dissolved nutrients, they also had high Brix values (12.1+/-0.6, 6.5+/-01, 6.0+/-0.1, and 23.5+/-0.1, respectively). The Brix values of polymeric diet had a linear additive relationship with the diet formula concentration at various pHs, temperatures, and in the gastric juice. Conclusion: Brix value measurement can be used to monitor stomach dietary formula concentration. Such information can be obtained at the bedside and used to evaluate feeding-intolerant patients receiving enteral feeding. (C) 2002 Elsevier Science Ltd. All rights reserved.