What are the nutritional components and daily volume requirements of a standard Total Parenteral Nutrition (TPN) regimen for a critically ill infant?

Standard TPN Composition and Volume Requirements for Critically Ill Infants

For a critically ill infant, withhold full parenteral nutrition (including amino acids and lipids) for up to one week while providing only glucose, electrolytes, and micronutrients at maintenance fluid volumes of 100-150 mL/kg/day, as this approach reduces infections, ventilator days, and PICU length of stay. 1

Initial Management Strategy (First Week)

Provide glucose and micronutrients only, not complete TPN:

• Glucose solution: Mix 60% dextrose 5% with 40% NaCl 0.9% at maintenance fluid rates 1
• Glucose delivery rate: 10-12 mg/kg/min to prevent hypoglycemia without causing hyperglycemia 2
• Target blood glucose: Maintain >70 mg/dL to suppress protein catabolism 2
• Fluid volume: 100-150 mL/kg/day for term infants, up to 150-180 mL/kg/day if metabolic clearance needed 2
• Essential addition: Provide intravenous minerals, trace elements, and vitamins from day 1 1

This "late PN" strategy from the landmark PEPaNIC trial demonstrated superior outcomes compared to early full TPN, with significantly fewer infections, reduced ventilator dependence, less kidney failure, and shorter hospital stays 1.

Energy Requirements

Acute phase (days 1-2):

• Energy intake should equal or be lower than resting energy expenditure (REE) 1
• Use Schofield formula for weight to estimate REE—do NOT add stress or activity factors 1
• Most critically ill children have an acute metabolic stress period lasting only 1-2 days 1

Recovery phase (after day 2-7):

• Increase energy to 1.3-1.5 times measured REE to enable tissue repair and growth 1
• Minimum intake of 57 kcal/kg/day required to achieve protein anabolic state 1

When to Initiate Complete TPN (After Day 7-8)

If enteral nutrition remains inadequate after one week, initiate full TPN with these components:

Amino Acids (Protein)

• Term infants: Start 1.5 g/kg/day, advance to maximum 3.0 g/kg/day 3
• Preterm infants: Start 1.5 g/kg/day on day 1, advance to 2.5-3.5 g/kg/day from day 2 3
• Minimum protein: 1.5 g/kg/day to avoid negative nitrogen balance 1, 3
• Non-protein calories: Ensure minimum 30-40 kcal per 1g amino acids for proper utilization 3

Lipids

• Dose: 1-3 g/kg/day when TPN is initiated 4
• Type: Composite lipid emulsions with or without fish oil as first-line choice 1
• Monitoring: Check triglycerides frequently in septic infants; reduce dose if hyperlipidemia develops but maintain at least essential fatty acid requirements 1

Carbohydrates

• Glucose: Sufficient to prevent hypoglycemia but not excessive to avoid hyperglycemia 1
• Rate: Continue 10-12 mg/kg/min, do not exceed this to prevent lipogenesis 2

Micronutrients

• Essential from day 1: Minerals, trace elements, and vitamins must be provided even when withholding macronutrients 1
• Carnitine: Consider supplementation if PN expected >4 weeks 1

Critical Exceptions to Delayed TPN

Initiate earlier TPN (before day 7) only in:

• Severely malnourished infants at baseline 1
• Infants unable to receive ANY enteral nutrition during first week 1
• Infants at high risk of nutritional deterioration 1

Volume Calculations

Total daily fluid volume:

• Standard maintenance: 100-150 mL/kg/day for most term infants 2
• Higher volumes: Up to 150-180 mL/kg/day if enhanced metabolic clearance needed 2
• Adjust for: Enteral nutrition volume and micronutrient infusion volumes 1

Common Pitfalls to Avoid

• Do not start full TPN within 24 hours in previously well-nourished critically ill infants—this increases infections and complications 1
• Do not use prediction equations with stress factors—Schofield formula for weight alone is sufficient 1
• Do not withhold micronutrients—vitamins, minerals, and trace elements must be given even when withholding macronutrients 1
• Monitor glucose every 2-4 hours initially—hypoglycemia incidence increases from 4.8% to 9.1% with delayed PN but is manageable 1
• Do not exceed 3.5 g/kg/day amino acids in preterm infants—higher doses cause imbalances without benefit 3
• Avoid insufficient non-protein calories—impairs amino acid utilization and wastes protein 3

Monitoring Requirements

• Glucose: Every 2-4 hours initially, use blood gas analyzer not handheld meter in critically ill infants 2
• Triglycerides: Frequent monitoring especially in septic infants 1
• Electrolytes: Based on serum levels, adjust additions accordingly 2
• Growth parameters: Weight, length tracking after acute phase 1