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TPN & Nutrition Calculation Practice

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Total parenteral nutrition problems total the calories from dextrose, amino acids, and lipids. The IV energy densities are not the familiar oral macronutrient values, and the exam tests that difference directly.

FormulasIV: dextrose 3.4 kcal/g • protein 4 kcal/g • 20% lipid = 2 kcal/mLOral/enteral: carbohydrate 4 kcal/g • protein 4 kcal/g • fat 9 kcal/ggrams of nitrogen = grams of protein ÷ 6.25
Worked example

Calories from 1,000 mL of dextrose 20%? Grams = 1,000 × 20% = 200 g; 200 × 3.4 = 680 kcal.

Read the ask: total vs nonprotein kcal changes whether you include the amino acid calories.

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TPN, Dextrose kcal
A TPN contains 100 mL of dextrose 25%. How many kilocalories does the dextrose provide? (IV dextrose = 3.4 kcal/g) Round your answer to the nearest whole number.
kcal

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How to set up a TPN calorie problem

A parenteral nutrition question gives you the volumes and strengths of the three macronutrient components and asks for the calories, either all of them or just the nonprotein ones. The arithmetic is percent-to-grams followed by grams-to-kilocalories. The trap is that the calorie values for IV nutrition are not the ones you learned for food, and the exam tests the difference directly.

IV: dextrose 3.4 kcal/g  •  amino acids 4 kcal/g  •  20% lipid 2 kcal/mL  •  10% lipid 1.1 kcal/mL

Oral/enteral: carbohydrate 4 kcal/g  •  protein 4 kcal/g  •  fat 9 kcal/g

IV dextrose is 3.4 rather than 4 because the dextrose in a bag is the monohydrate, and the water of hydration is weight that provides no energy. Lipid emulsions are given per millilitre rather than per gram because the emulsion's calories include the glycerol and egg phospholipid, not just the oil; the question will state the value. Amino acids are 4 either way.

Worked example 1: one component

How many kilocalories are in 500 mL of dextrose 50%?

grams = 500 × 50% = 250 g

kcal = 250 × 3.4 = 850 kcal

Worked example 2: total and nonprotein calories

A TPN contains 1,000 mL of dextrose 25%, 500 mL of amino acids 8.5%, and 250 mL of 20% lipid emulsion.

dextrose = 1,000 × 25% = 250 g

dextrose kcal = 250 × 3.4 = 850 kcal

protein = 500 × 8.5% = 42.5 g

protein kcal = 42.5 × 4 = 170 kcal

lipid kcal = 250 × 2 = 500 kcal

total = 850 + 170 + 500 = 1,520 kcal

nonprotein = 850 + 500 = 1,350 kcal

Both figures are asked for, in different questions, for a reason: nonprotein calories are what the dietitian counts against energy needs, on the principle that the amino acids are there to build protein, not to be burned. The word "nonprotein" in the stem means leave the amino acid calories out. "Total" means include them. Everything else in the two calculations is identical.

Worked example 3: grams of nitrogen

How many grams of nitrogen does 500 mL of 10% amino acids provide? (Protein is 16% nitrogen, so nitrogen = protein ÷ 6.25.)

protein = 500 × 10% = 50 g

nitrogen = 50 ÷ 6.25 = 8 g

This feeds calorie-to-nitrogen ratio questions: nonprotein kcal divided by grams of nitrogen. Using example 2's bag with this amino acid volume would be 1,350 ÷ 8, about 169:1. You don't need to memorize a target ratio for the exam; you need to be able to compute one.

Worked example 4: an oral supplement

A serving contains 30 g carbohydrate, 10 g protein and 6 g fat.

kcal = 30 × 4 + 10 × 4 + 6 × 9 = 214 kcal

Oral and enteral products use the food values. Reading "carbohydrate" and reaching for 3.4 is the mirror image of the IV mistake.

Where students lose the points

10 TPN & Nutrition Calculation practice problems with worked solutions

Every problem below is worked start to finish. Try it yourself first, then check the steps. For a fresh problem every time, use the practice box above. It generates unlimited variations of these same question types.

Problem 1: TPN, Dextrose kcal

A TPN contains 1000 mL of dextrose 20%. How many kilocalories does the dextrose provide? (IV dextrose = 3.4 kcal/g) Round your answer to the nearest whole number.

Answer 680 kcal

Solution
  1. Grams of dextrose: 1000 mL × 20% = 200 g.
  2. kcal = 200 g × 3.4 kcal/g = 680 kcal.
  3. Rounded as the question asks: 680 kcal.

IV (TPN) energy densities: dextrose 3.4 kcal/g, protein 4 kcal/g, lipid 10% = 1.1 kcal/mL, 20% = 2 kcal/mL. ORAL/enteral nutrition uses 4 kcal/g carbohydrate, 4 protein, 9 fat. Don't mix the two systems.

Problem 2: TPN, Nitrogen

A TPN contains 1000 mL of 10% amino acids. How many grams of nitrogen does it provide? (Protein is 16% nitrogen: N = protein ÷ 6.25) Round your answer to one decimal place.

Answer 16.0 g

Solution
  1. Protein grams: 1000 mL × 10% = 100 g.
  2. Nitrogen = 100 g protein ÷ 6.25 g protein/g N = 16 g N.
  3. Rounded as the question asks: 16.0 g.

Lower-yield for the exam, kept for completeness. Used for nitrogen-balance and calorie:nitrogen ratio questions.

Problem 3: TPN, Total kcal

A TPN contains 1500 mL dextrose 50%, 1000 mL amino acids 15%, and 500 mL of 20% lipid emulsion. What are the total kilocalories? (3.4 kcal/g dextrose, 4 kcal/g protein, 20% lipid = 2 kcal/mL) Round your answer to the nearest whole number.

Answer 4,150 kcal

Solution
  1. Dextrose: 1500 mL × 50% = 750 g; × 3.4 kcal/g = 2550 kcal.
  2. Protein: 1000 mL × 15% = 150 g; × 4 kcal/g = 600 kcal.
  3. Lipid: 500 mL × 2 kcal/mL = 1000 kcal.
  4. Total = 2550 + 600 + 1000 = 4150 kcal.
  5. Rounded as the question asks: 4,150 kcal.

Total vs NONPROTEIN kcal is decided by the question's wording, so read the ask twice before adding.

Problem 4: Oral Nutrition kcal

An oral nutrition supplement contains 20 g carbohydrate, 6 g protein, and 2 g fat per serving. How many kilocalories per serving? (Oral: 4 kcal/g carbohydrate, 4 kcal/g protein, 9 kcal/g fat) Round your answer to the nearest whole number.

Answer 122 kcal

Solution
  1. Carbohydrate: 20 g × 4 kcal/g = 80 kcal.
  2. Protein: 6 g × 4 kcal/g = 24 kcal.
  3. Fat: 2 g × 9 = 18 kcal.
  4. Total = 80 + 24 + 18 = 122 kcal.
  5. Rounded as the question asks: 122 kcal.

The oral/enteral system (4/4/9) differs from IV: oral carbohydrate is 4 kcal/g, but IV dextrose monohydrate is 3.4 kcal/g. Route determines the numbers.

Problem 5: TPN, Nonprotein kcal

A TPN contains 1500 mL dextrose 30%, 250 mL amino acids 8.5%, and 500 mL of 20% lipid emulsion. What are the NONPROTEIN kilocalories? (3.4 kcal/g dextrose, 4 kcal/g protein, 20% lipid = 2 kcal/mL) Round your answer to the nearest whole number.

Answer 2,530 kcal

Solution
  1. Dextrose: 1500 mL × 30% = 450 g; × 3.4 kcal/g = 1530 kcal.
  2. Protein: 250 mL × 8.5% = 21.25 g; × 4 kcal/g = 85 kcal, excluded: the question asks for nonprotein kcal.
  3. Lipid: 500 mL × 2 kcal/mL = 1000 kcal.
  4. Nonprotein = 1530 + 1000 = 2530 kcal.
  5. Rounded as the question asks: 2,530 kcal.

Total vs NONPROTEIN kcal is decided by the question's wording, so read the ask twice before adding.

Problem 6: TPN, Dextrose kcal

A TPN contains 250 mL of dextrose 50%. How many kilocalories does the dextrose provide? (IV dextrose = 3.4 kcal/g) Round your answer to the nearest whole number.

Answer 425 kcal

Solution
  1. Grams of dextrose: 250 mL × 50% = 125 g.
  2. kcal = 125 g × 3.4 kcal/g = 425 kcal.
  3. Rounded as the question asks: 425 kcal.

IV (TPN) energy densities: dextrose 3.4 kcal/g, protein 4 kcal/g, lipid 10% = 1.1 kcal/mL, 20% = 2 kcal/mL. ORAL/enteral nutrition uses 4 kcal/g carbohydrate, 4 protein, 9 fat. Don't mix the two systems.

Problem 7: TPN, Nitrogen

A TPN contains 500 mL of 5% amino acids. How many grams of nitrogen does it provide? (Protein is 16% nitrogen: N = protein ÷ 6.25) Round your answer to one decimal place.

Answer 4.0 g

Solution
  1. Protein grams: 500 mL × 5% = 25 g.
  2. Nitrogen = 25 g protein ÷ 6.25 g protein/g N = 4 g N.
  3. Rounded as the question asks: 4.0 g.

Lower-yield for the exam, kept for completeness. Used for nitrogen-balance and calorie:nitrogen ratio questions.

Problem 8: TPN, Total kcal

A TPN contains 500 mL dextrose 20%, 250 mL amino acids 4.25%, and 250 mL of 20% lipid emulsion. What are the total kilocalories? (3.4 kcal/g dextrose, 4 kcal/g protein, 20% lipid = 2 kcal/mL) Round your answer to the nearest whole number.

Answer 883 kcal

Solution
  1. Dextrose: 500 mL × 20% = 100 g; × 3.4 kcal/g = 340 kcal.
  2. Protein: 250 mL × 4.25% = 10.625 g; × 4 kcal/g = 42.5 kcal.
  3. Lipid: 250 mL × 2 kcal/mL = 500 kcal.
  4. Total = 340 + 42.5 + 500 = 882.5 kcal.
  5. Rounded as the question asks: 883 kcal.

Total vs NONPROTEIN kcal is decided by the question's wording, so read the ask twice before adding.

Problem 9: Oral Nutrition kcal

An oral nutrition supplement contains 35 g carbohydrate, 20 g protein, and 6 g fat per serving. How many kilocalories per serving? (Oral: 4 kcal/g carbohydrate, 4 kcal/g protein, 9 kcal/g fat) Round your answer to the nearest whole number.

Answer 274 kcal

Solution
  1. Carbohydrate: 35 g × 4 kcal/g = 140 kcal.
  2. Protein: 20 g × 4 kcal/g = 80 kcal.
  3. Fat: 6 g × 9 = 54 kcal.
  4. Total = 140 + 80 + 54 = 274 kcal.
  5. Rounded as the question asks: 274 kcal.

The oral/enteral system (4/4/9) differs from IV: oral carbohydrate is 4 kcal/g, but IV dextrose monohydrate is 3.4 kcal/g. Route determines the numbers.

Problem 10: TPN, Nonprotein kcal

A TPN contains 500 mL dextrose 40%, 250 mL amino acids 15%, and 100 mL of 20% lipid emulsion. What are the NONPROTEIN kilocalories? (3.4 kcal/g dextrose, 4 kcal/g protein, 20% lipid = 2 kcal/mL) Round your answer to the nearest whole number.

Answer 880 kcal

Solution
  1. Dextrose: 500 mL × 40% = 200 g; × 3.4 kcal/g = 680 kcal.
  2. Protein: 250 mL × 15% = 37.5 g; × 4 kcal/g = 150 kcal, excluded: the question asks for nonprotein kcal.
  3. Lipid: 100 mL × 2 kcal/mL = 200 kcal.
  4. Nonprotein = 680 + 200 = 880 kcal.
  5. Rounded as the question asks: 880 kcal.

Total vs NONPROTEIN kcal is decided by the question's wording, so read the ask twice before adding.

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