title: Validation the use of refractometer and mathematic equations to measure dietary formula contents for clinical application.
abstract: OBJECTIVE
  Gastric residual volumes are widely used to evaluate gastric emptying for patients receiving enteral feeding, but controversy exists about what constitutes gastric residual volume. We have developed a method by using refractometer and derived mathematical equations to calculate the formula concentration, total residual volume (TRV), and formula volume. In this study, we like to validate these mathematical equations before they can be implemented for clinical patient care.
  
  
  METHODS
  Four dietary formulas were evaluated in two consecutive validation experiments. Firstly, dietary formula volume of 50, 100, 200, and 400 ml were diluted with 50 ml water, and then the Brix value (BV) was measured by the refractometer. Secondly, 50 ml of water, then 100 ml of dietary formula were infused into a beaker, and followed by the BV measurement. After this, 50 ml of water was infused and followed by the second BV measurement. The entire procedure of infusing of dietary formula (100 ml) and waster (50 ml) was repeated twice and followed by the BV measurement.
  
  
  RESULTS
  The formula contents (formula concentration, TRV, and formula volume) were calculated by mathematical equations. The calculated formula concentrations, TRVs, and formula volumes measured from mathematic equations were strongly close to the true values in the first and second validation experiments (R2>0.98, P<0.001).
  
  
  CONCLUSIONS
  Refractometer and the derived mathematical equations may be used to accurately measure the formula concentration, TRV, and formula volume and served as a tool to monitor gastric emptying for patients receiving enteral feeding.
authors.affiliation: Division of Gastroenterology, Department of Internal Medicine, National Defense Medical Center, Taipei, Taiwan, Republic of China.
authors.forename: W-K
authors.initials: WK
authors.lastname: Chang
authors.forename: Y-C
authors.initials: YC
authors.lastname: Chao
authors.forename: S-A
authors.initials: SA
authors.lastname: Mcclave
authors.forename: M-K
authors.initials: MK
authors.lastname: Yeh
mesh_terms: D004750:Enteral Nutrition / Q000379:methods; D005526:Food, Formulated / Q000032:analysis*; D005746:Gastric Emptying / Q000502:physiology*; D005766:Gastrointestinal Contents / Q000737:chemistry*; D006801:Humans; D008433:Mathematics; D008954:Models, Biological; D012031:Refractometry / Q000379:methods / Q000592:standards*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity