Step-by-Step Calculations for Pediatric Parenteral Nutrition
Design parenteral nutrition for pediatric patients by calculating weight-based requirements for energy, protein, lipids, carbohydrates, fluids, and micronutrients, with specific targets varying by age group (preterm infants, term infants, and children).
Step 1: Determine Patient Weight and Age Category
- Obtain accurate current weight in kilograms – this is the foundation for all calculations 1
- Classify patient into age group:
- Preterm infants (<37 weeks gestation)
- Term infants (0-12 months)
- Children (>1 year)
Step 2: Calculate Energy Requirements
For Preterm and Very Low Birth Weight Infants:
- Target: 90-120 kcal/kg/day for parenteral nutrition 2
- This is lower than enteral requirements (110-135 kcal/kg/day) because PN bypasses splanchnic metabolism and eliminates stool losses (approximately 30 kcal/kg/day difference) 2
- Start at lower end (90 kcal/kg/day) and advance based on growth response 2
For Term Infants and Children:
- Use Schofield's equation to calculate resting energy expenditure 3
- Add energy for growth and activity
- Typical range: 80-100 kcal/kg/day for older children, decreasing with age 3
Calculation Example (2 kg preterm infant):
- 2 kg × 100 kcal/kg/day = 200 kcal/day total energy target
Step 3: Calculate Protein (Amino Acid) Requirements
For Preterm Infants:
- Start: 2.5-3.5 g/kg/day from postnatal day 2 onwards 3
- Maximum: Do not exceed 3.5 g/kg/day 3
- Must be accompanied by non-protein energy >65 kcal/kg/day 3
For Term Infants and Children:
- Target: 1.5-3.0 g/kg/day depending on age and clinical status 3
- Younger infants require higher amounts per kg
Calculation Example (2 kg preterm infant):
- 2 kg × 3.0 g/kg/day = 6 g amino acids/day
Step 4: Calculate Lipid Requirements
For Preterm Infants:
- Start immediately after birth or by day 2 of life 4
- Target: 2-4 g/kg/day maximum 4
- Minimum: 0.25 g/kg/day linoleic acid to prevent essential fatty acid deficiency 4
- Use 20% lipid emulsions as first choice 4
- Infuse continuously over 24 hours 4
- Use composite lipid emulsions with or without fish oil (avoid pure soybean oil for >few days) 4
- Protect with light-protected tubing 4
For Term Infants:
For Children:
- Maximum: 3 g/kg/day 4
- Minimum: 0.1 g/kg/day linoleic acid 4, 5
- Maximal lipid oxidation rate is approximately 3 g/kg/day in young children 4
Calculation Example (2 kg preterm infant):
- 2 kg × 3.0 g/kg/day = 6 g lipids/day
- Using 20% lipid emulsion: 6 g ÷ 0.2 = 30 mL/day
Step 5: Calculate Carbohydrate (Dextrose) Requirements
- Calculate remaining energy needs after accounting for protein and lipids
- Protein provides 4 kcal/g; lipids provide 9-10 kcal/g; dextrose provides 3.4 kcal/g 2
- Maximum glucose infusion rate: 12 mg/kg/min (17.3 g/kg/day) in children 4
Calculation Example (2 kg preterm infant targeting 200 kcal/day):
- Protein energy: 6 g × 4 kcal/g = 24 kcal
- Lipid energy: 6 g × 10 kcal/g = 60 kcal
- Remaining energy needed: 200 - 24 - 60 = 116 kcal
- Dextrose needed: 116 kcal ÷ 3.4 kcal/g = 34 g/day
- Check maximum: 34 g ÷ 2 kg = 17 g/kg/day (within safe limit of 17.3 g/kg/day)
Step 6: Calculate Fluid Requirements
Preterm infants: Highly variable based on gestational age, postnatal age, and insensible losses
- Day 1: 70-100 mL/kg/day
- Advance gradually based on clinical status
- May require 120-150 mL/kg/day by end of first week 1
Term infants and children:
- Use standard maintenance fluid calculations (e.g., Holliday-Segar method)
- Adjust for clinical conditions requiring fluid restriction 5
Calculation Example (2 kg preterm infant, day 3):
- 2 kg × 120 mL/kg/day = 240 mL/day total fluid
Step 7: Determine Dextrose Concentration
- Calculate dextrose concentration based on total dextrose needed and total fluid volume
- Common concentrations: 10-12.5% for peripheral PN; up to 20-25% for central PN 1
Calculation Example:
- 34 g dextrose ÷ 240 mL = 0.142 = 14.2% dextrose concentration
- This requires central venous access
Step 8: Add Electrolytes, Minerals, and Micronutrients
- Sodium: 2-4 mEq/kg/day (adjust based on serum levels)
- Potassium: 2-3 mEq/kg/day (adjust based on serum levels)
- Calcium:
- Phosphorus: Maintain Ca:P ratio approximately 1.3-1.7:1 (mg:mg)
- Magnesium: 0.3-0.5 mEq/kg/day
- Trace elements: Use age-appropriate commercial multi-trace element solutions 3
- Vitamins: Use pediatric multivitamin preparations 3
Important considerations:
- Remove chromium from trace element supplementation 3
- Consider carnitine supplementation if PN expected >4 weeks 4
- Do not routinely add heparin to lipid infusions 4
Step 9: Verify Calculations and Safety Limits
- Confirm protein:energy ratio is adequate (non-protein calories >65 kcal/kg/day with amino acids) 3
- Verify glucose infusion rate does not exceed 12 mg/kg/min 4
- Check lipid dose does not exceed maximum for age group 4
- Ensure osmolarity is appropriate for route of administration (peripheral vs central)
- Use computerized ordering systems when available to reduce calculation errors 6
Step 10: Adjust Based on Clinical Response
- Monitor growth parameters daily (weight) and weekly (length, head circumference)
- Adjust energy intake if growth failure occurs (dropping across weight centiles) 2
- Monitor biochemical parameters: glucose, triglycerides, electrolytes, liver function, albumin
- Transition to enteral nutrition as quickly as clinically feasible 1
Common Pitfalls to Avoid
- Do not delay lipid initiation in preterm infants – start by day 2 of life at latest 4
- Do not use pure soybean oil emulsions for >few days – use composite emulsions 4
- Do not exceed maximum amino acid dose of 3.5 g/kg/day in preterm infants 3
- Do not ignore minimal enteral feeds when calculating total intake – though absorption may be negligible at <25 mL/kg/day 2
- Do not use standardized PN solutions in metabolically unstable patients or those with abnormal losses – these require individualized formulations 7
- Do not forget light protection for lipid infusions in preterm infants 4