Total Parenteral Nutrition in ICU
Initiate TPN within 24-48 hours in critically ill ICU patients who cannot receive enteral nutrition, but only after attempting enteral feeding first, as enteral nutrition significantly reduces infectious complications and mortality compared to TPN. 1, 2
When to Initiate TPN
Primary Indication
- Start TPN within 24-48 hours if enteral nutrition (EN) cannot be initiated or is contraindicated in patients not expected to resume normal oral nutrition within 3 days 1
- These guidelines apply specifically to ICU patients with organ failure (SOFA > 4) and expected ICU stay longer than 3 days 1
Critical Timing Considerations
- Enteral nutrition must be attempted first within 48 hours of ICU admission in hemodynamically stable patients with functioning gastrointestinal tracts 1, 2
- Early EN reduces infectious complications by 50% compared to early TPN (RR 0.50, CI 0.37-0.67) and shortens both ICU and hospital stays 2
- If EN fails to meet nutritional requirements after 3-7 days, particularly in severely malnourished patients, initiate supplemental or total parenteral nutrition 1, 2
Contraindications to Enteral Nutrition (When TPN Becomes Necessary)
- Non-functioning gastrointestinal tract 1, 2
- Hemodynamic instability requiring high-dose vasopressors 3
- Severe feeding intolerance despite post-pyloric feeding attempts 4
TPN Composition and Dosing
Energy Requirements
- Acute phase (first 72-96 hours): Start with 20-25 kcal/kg/day to avoid overfeeding 1, 5
- Recovery/anabolic phase: Increase to 25-30 kcal/kg/day 5
- Avoid hyperalimentation as it increases mortality and infectious complications 1, 6
Macronutrient Targets
- Protein: 1.3-1.5 g/kg ideal body weight/day with a balanced amino acid mixture 1
- L-glutamine supplementation: 0.2-0.4 g/kg/day (Grade A recommendation) 1
- Carbohydrates: Minimum 2 g/kg/day of glucose 5
- Lipids: 0.7-1.5 g/kg/day administered over 12-24 hours 1
Micronutrients
- All TPN prescriptions must include daily multivitamins and trace elements 1
Administration Route
Central vs. Peripheral Access
- Central venous access is required for high osmolarity TPN mixtures designed to cover full nutritional needs 1, 7
- Peripheral venous access may be considered only for low osmolarity (<850 mOsmol/L) mixtures covering partial nutritional needs 1
- If peripheral TPN cannot provide full nutritional requirements, switch to central administration 1, 7
Delivery Method
- Administer TPN as a complete all-in-one bag (Grade B recommendation) 1
Critical Pitfalls to Avoid
Overfeeding Complications
- Hyperglycemia is a major risk factor that increases mortality and infectious complications in critically ill patients 1, 5
- Maintain blood glucose between 4.5-10 mmol/L (81-180 mg/dL) 5
- Excessive dextrose or lipid administration can impair reticuloendothelial system function and increase infection risk 6
Underfeeding Consequences
- Energy deficits correlate strongly with infectious complications, duration of mechanical ventilation, and ICU length of stay 1
- Malnutrition affects up to 50% of ICU patients and significantly worsens outcomes 1, 8
Timing Errors
- Delaying nutritional support beyond 3 days in patients unable to eat is harmful 1
- Starting TPN before attempting EN misses the opportunity to reduce infectious complications by 36% (RR 0.64,95% CI 0.48-0.87) 1
Monitoring Requirements
- Strict glucose monitoring to prevent hyperglycemia-associated complications 1, 5
- Electrolyte monitoring, particularly potassium, magnesium, and phosphate for refeeding syndrome 5, 4
- Assessment for feeding tolerance and complications 4