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Equation of Nelson et al for Predicting the Refractive Index (RI) for a Parenteral Nutrition Solution

Description

A pharmacy or other department may be asked to make a parenteral nutrition solution. Comparing the refractive index (RI) of the solution against the predicted refractive index is one way of seeing if the solution was made correctly. The authors are from the University of Utah.


 

Method:

(1) The solution is made up according to its formula.

(2) The refractive index of the final solution is measured.

(3) This is compared to the predicted refractive index based on the following formula:

 

final refractive index =

= 1.33 + (SUM((RI for concentrate) * (volume of concentrate in mL)) / (total volume of parenteral nutrient solution in mL))

 

difference between the observed and predicted RI =

= (RI observed) – (RI predicted)

 

Interpretation:

• The observed RI should match the predicted RI closely.

• If there is a significant difference then the formula for making up the solution should be checked. If the cause cannot be identified then the solution should be remade.

 

Other measures that can be used:

(1) electrolyte concentration

(2) glucose concentration

 


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Specialty

ICD-10