Clinical & Hospital Pharmacy
TPN Admixture Calculator
Builds a total parenteral nutrition bag from weight-based macronutrient targets: volumes, calories, nitrogen balance, osmolarity and the ASPEN safety checks.
Educational tool — not a compounding order
Final osmolarity
1532mOsm/L
Suitable for central line administration
Patient & access
Target: 2100 mL/day
Macronutrients
Weight-based targets, converted to stock-solution volumes.
Total 84.0 g/day → 840.0 mL
Total 210.0 g/day → 300.0 mL
Total 70.0 g/day → 350.0 mL
Glucose infusion rate (GIR): 2.08 mg/kg/min. Within the typical range (max ~5 mg/kg/min).
Electrolytes
Per-day totals added to the bag.
1–2 mEq/kg/day
1–2 mEq/kg/day
10–15 mEq/day
8–20 mEq/day
20–40 mmol/day
Additives
Optional. MVI and trace elements add to the bag volume.
Recorded on the order; adds no volume here.
Recorded on the order; adds no volume here.
Final bag composition
What the compounder needs to draw up.
Bag volume breakdown
| Component | Amount | Volume |
|---|---|---|
| Amino Acids 10% | 84.0 g | 840.0 mL |
| Dextrose 70% | 210.0 g | 300.0 mL |
| Lipid Emulsion 20% | 70.0 g | 350.0 mL |
| Electrolytes (approx. stock) | — | 11.1 mL |
| Multivitamin + trace elements | — | 11.0 mL |
| Sterile water (to volume) | — | 587.9 mL |
| Final bag | — | 2100 mL |
Each macronutrient goes from a weight-based dose to grams, then to a stock volume:
grams = dose (g/kg/day) × weight (kg)
volume (mL) = grams / (concentration % / 100)
Calories use 4 kcal/g for amino acids, 3.4 kcal/g for dextrose (monohydrate) and 10 kcal/g for 20% and 30% lipid emulsions (9 kcal/g for 10%). Nitrogen is 16% of amino acid grams.
GIR (mg/kg/min) = dextrose g × 1000 / (weight × 1440)
NPC:N = non-protein kcal / nitrogen g
Osmolarity uses the standard clinical approximation:
mOsm = (dextrose g × 5) + (amino acid g × 10) + Σ(electrolyte × mOsm factor)
osmolarity (mOsm/L) = total mOsm / total volume (mL) × 1000
Sterile water makes the component volume up to the fluid goal, and the infusion rate is the final bag volume over 24 hours. Peripheral administration is flagged above 900 mOsm/L, with a caution from 750.
Common questions
Parenteral dextrose is the monohydrate, which carries a water molecule, so each gram yields about 3.4 kcal rather than the 4 kcal of anhydrous carbohydrate. Using 4 would overstate the calories by about 18%.
Whether there is enough non-protein energy for the amino acids to be used for building tissue instead of being burned for fuel. Around 100–150:1 suits most patients; a lower ratio suits catabolic or critically ill patients needing more protein, and a higher one suits stable patients.
A peripheral vein cannot tolerate a strongly hypertonic solution — above roughly 900 mOsm/L the risk of phlebitis, pain and extravasation climbs sharply. Central lines empty into a high-flow vessel where the admixture is diluted immediately, so they carry no practical limit.
No, and that is the most important thing it does not do. Calcium phosphate precipitation is a recognised cause of fatal pulmonary emboli in TPN. Always check the amounts against the manufacturer's solubility curve for the specific amino acid product and final volume.
Prepared by the PharmaWallah student team. Verify results with your textbook or instructor. Report an error · Editorial policy