Parenteral nutrition calorie worksheet

What is this for?

Parenteral calorie densities differ from dietary ones. Dextrose monohydrate supplies 3.4 kcal/g rather than 4, because the hydrated form carries water weight. Lipid emulsion is expressed per millilitre rather than per gram, and includes calories from the glycerol and phospholipid excipients.

How to use it

1. Enter the total volume of the dextrose/amino acid portion of the bag and the final percentage of each. These are the concentrations in the finished bag, not the stock concentrations.
2. Select the lipid emulsion concentration and enter the volume infused.
3. Optionally add the weight to get kcal/kg, g protein/kg, and the glucose infusion rate.

Worked example

A 2 litre bag is compounded to a final concentration of 15% dextrose and 4% amino acids, with 250 mL of 20% lipid emulsion. Calculate the daily calories for a 70 kg patient.

Answer: dextrose 300 g × 3.4 = 1020 kcal; amino acids 80 g × 4 = 320 kcal; lipid 250 × 2 = 500 kcal. Total 1840 kcal, which is 26.3 kcal/kg. Protein 1.14 g/kg/day. Non-protein calories 1520, nitrogen 12.8 g, so NPC:N is 119:1.

Clinical pearls & pitfalls

• Dextrose monohydrate supplies 3.4 kcal/g, not 4. Using the dietary factor overstates the calories by about 18% of the dextrose contribution.
• Lipid emulsion calories are per millilitre of emulsion, not per gram of fat. A 20% emulsion is 20 g of oil per 100 mL, but supplies 2.0 kcal/mL because glycerol and phospholipid contribute as well.
• The non-protein calorie to nitrogen ratio is the classic index of protein adequacy. A ratio around 150:1 is typical for a stable patient; a more catabolic patient needs proportionally more protein, giving a lower ratio of roughly 80–100:1.
• Watch the glucose infusion rate in critical illness. Above about 4–5 mg/kg/min, additional glucose is not oxidised and contributes to hyperglycaemia and hepatic steatosis.
• Percentages in a compounded bag are final concentrations. Confusing them with the stock solution strengths — 70% dextrose, 10% amino acids — produces a large error.

Assumptions & limitations

• Calculates macronutrient calories only. It does not address electrolytes, trace elements, vitamins, osmolarity, calcium-phosphate compatibility, or stability, all of which are essential parts of a parenteral nutrition order.
• Assumes the lipid is administered as stated. Separately hung lipid infused over a shorter period has different tolerance considerations.
• Does not verify that the calorie target is appropriate. Use the total energy expenditure calculator or indirect calorimetry to set the goal.

References

• Boullata JI, et al. ASPEN safe practices for parenteral nutrition. JPEN J Parenter Enteral Nutr. 2014;38(3):334-377.
• Worthington P, et al. When is parenteral nutrition appropriate? JPEN J Parenter Enteral Nutr. 2017;41(3):324-377.
• Mirtallo J, et al. Safe practices for parenteral nutrition. JPEN J Parenter Enteral Nutr. 2004;28(6):S39-S70.

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