Manual of Clinical Nutrition

Manual of Clinical Nutrition Management III- 99 Copyright © 2013 Compass Group, Inc.

CALCULATING TOTAL PARENTERAL NUTRITION

I. Steps for Calculating TPN.

Assess calorie, protein, and fluid requirements.

1. Determine calories to be provided as fat.


2. Convert fat calories to volume of lipid emulsion or lipid concentration in 3-in-1 solution (or
   total nutrient admixture TNA)


3. Determine calories provided from protein


4. Determine amino acid concentration.


5. Determine calories provided from carbohydrate.


6. Determine carbohydrate (dextrose) concentration.


7. Determine if final solution can be compounded.
   These steps will be outlined in detail below.
   II. Determine amount of each substrate. Guidelines for usual and maximum substrate amounts
   are provided in the Table. After these determinations have been made substrate concentrations
   are easily calculated based on TPN volume. End concentrations reflect grams of substrate in the
   final volume of TPN solution (see Table).
   Substrates in TPN
   SUBSTRATE USUSAL AMOUNT MAXIMUM UNITS OF SUBSTRATE
   Carbohydrate (cho) 40 - 60% of total Kcal <5 mg/kg/minute
   Protein (pro) 1.0-2.0 gm/kg/day 2.0-2.5 gm/kg/day
   Fat 20 - 40% daily total Kcal 2 gm/kg/day
   <1 gm/kg/day in high stress
   Note: Sample calculations are based on total calorie needs rather than nonprotein calorie needs. Either method may be
   used; however, the former yields approximately 250 to 350 calories more.
   Estimated Needs: 1,700 calories (kcal), 70 gm protein.
   III. Calculating macronutrient concentrations.
   A. 2 - in1 (traditional) solution calculations:
   Calculate 2-in-1 solution using 2,000 mL fluid (this volume will include lipid emulsion)


8. Determine kcal to be provided as fat.
   Estimated kcal x desired percent of fat = kcal as fat
   1,700 kcal x 30% = 510 kcal from fat


9. Convert fat kcal to volume of lipid emulsion.
   Fat kcal ÷ kcal/mL lipid emulsion = volume of lipid emulsion
   510 kcal ÷ 1.1 (10% emulsion) kcal/mL = 463 mL of 10% lipid
   or
   510 kcal ÷ 2.0 (20% emulsion) kcal/mL = 255 mL of 20% lipid
   Some institutions prefer lipid to be ordered in volumes as packaged by the supplier
   (250 mL or 500 mL).
   For this example, 500 mL of 10% lipid will be used leaving 1,500 ML for the remaining
   TPN solution.


10. Determine kcal to be provided from protein.
    Estimated protein needs x kcal/gm protein = 70 gm protein x 4 kcal/gm = 280 kcal
    protein


11. Determine amino acid concentration (AA).
    gm protein x 100 = % amino acids
    TPN volume
    70 gm x 100 = 4.7% amino acids
    1,500 mL


12. Determine kcal to be provided from carbohydrate.
    Estimated kcal needs – (kcal as fat + kcal as protein) = carbohydrate kcal
    1,700 kcal – (510 kcal + 280 kcal) = 910 kcal carbohydrate


13. Determine carbohydrate concentration.
    a. Carbohydrate kcal ÷ kcal/gm dextrose = gm dextrose
    910 kcal ÷ 3.4 kcal/gm = 268 gm dextrose
    Dextrose solutions are 3.4 kcal/gm rather than 4 kcal/gm
    b. gm dextrose x 100 = % dextrose
    volume TPN
    268 gm x 100 = 17.9% dextrose
    1,500 mL