title: Gastric residual volume (GRV) and gastric contents measurement by refractometry.
abstract: BACKGROUND
  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.
  
  
  METHODS
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Division of Gastroenterology, Department of Internal Medicine, Tri-Service General Hospital, Taipei, Taiwan, Republic of China.
authors.forename: Wei-Kuo
authors.initials: WK
authors.lastname: Chang
authors.forename: Stephen A
authors.initials: SA
authors.lastname: McClave
authors.forename: Chung-Bao
authors.initials: CB
authors.lastname: Hsieh
authors.forename: You-Chen
authors.initials: YC
authors.lastname: Chao
mesh_terms: D004750:Enteral Nutrition; D005260:Female; D005526:Food, Formulated / Q000032:analysis*; D005746:Gastric Emptying / Q000502:physiology*; D005766:Gastrointestinal Contents / Q000737:chemistry*; D005769:Gastrointestinal Motility; D006801:Humans; D007441:Intubation, Gastrointestinal / Q000379:methods*; D008297:Male; D008433:Mathematics; D008875:Middle Aged; D012031:Refractometry / Q000379:methods / Q000592:standards*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013270:Stomach