Refractometry allows to identify the nature of gastric contents and thus allows to separate between gastric secretions and undigested food [1]. In case of delayed gastric emptying, the refractive index is higher [1].
Feasibility/Equipment: Refractometry requires training of personnel, but the handling and testing is simple.
Scoring information: The refractive index, also known as the Brix value(BV) correlates closely with the molar fractions of the components [1]. It may produce precise readings with only minimal variability [1].
Cost: Cost of equipment is low.
Evidence: Three studies, all from the same study group, have assessed refractometry in the settings of critically ill patients [1-3]. Refractometry may be used to assess gastric composition and may serve as a tool to monitor contents of the stomach [3].
Accuracy / measurement properties: Mean BV for patients with higher GRV (> 75ml) were higher in a series of 2 measurements 79+/-2% vs. 20+/-4%, respectively, P<0.05 and 59+/-7% vs 32+/-5%, respectively, P<0.05 [2].
References
1. Chang W, McClave S, Lee M, Chao Y: Monitoring bolus nasogastric tube feeding by the Brix value determination and residual volume measurement of gastric contents. Journal of Parenteral and Enteral Nutrition 2004, 28(2):105-112.
2. Chang WK, McClave SA, Chao YC: Continuous nasogastric tube feeding: monitoring by combined use of refractometry and traditional gastric residual volumes. Clin Nutr 2004, 23(1):105-112.
3. Chang WK, McClave SA, Hsieh CB, Chao YC: Gastric residual volume (GRV) and gastric contents measurement by refractometry. JPEN J Parenter Enteral Nutr 2007, 31(1):63-68.