What are the guidelines for initiating Total Parenteral Nutrition (TPN) in a critically ill patient?

TPN Initiation Guidelines in Critically Ill Patients

Initiate TPN within 24-48 hours only if enteral nutrition (EN) is contraindicated or cannot be tolerated in patients not expected to resume normal oral nutrition within 3 days. 1, 2

Timing Algorithm for TPN Initiation

First Priority: Attempt Enteral Nutrition

• Always attempt EN first within 48 hours of ICU admission in hemodynamically stable patients with functioning gastrointestinal tracts 2
• EN reduces infectious complications by 50% (RR 0.50,95% CI 0.37-0.67) compared to early TPN and shortens ICU/hospital stays 3, 2
• Only proceed to TPN after all strategies to maximize EN tolerance have been exhausted 1

When to Start TPN: Risk-Stratified Approach

High Nutritional Risk Patients (severely malnourished):

• Initiate TPN after 3 days if EN remains insufficient or not feasible 3, 2
• Consider early and progressive PN in severely malnourished patients 1

Low Nutritional Risk Patients:

• Withhold TPN for the first 7 days if receiving some EN 1, 3
• For patients tolerating partial EN, consider supplemental PN only after 7-10 days if unable to meet >60% of energy and protein requirements 1

Hemodynamic Stability Requirements Before TPN

• Delay all nutrition support if shock is uncontrolled and tissue perfusion goals are not reached 3
• Specific contraindications include: vasopressor requirements exceeding 1 μg/kg/min norepinephrine, uncontrolled life-threatening hypoxemia, hypercapnia, acidosis, or overt bowel ischemia 3
• Once shock is controlled, start low-dose EN (10-20 mL/hour) first, even if vasopressors are still required at lower doses 3

TPN Composition and Dosing

Energy Requirements

• Provide 25 kcal/kg/day during acute phase, increasing to target over 2-3 days 1, 2
• Aim to provide energy as close as possible to measured energy expenditure (use indirect calorimetry when available) to decrease negative energy balance 1
• During acute phase (days 1-7), provide hypocaloric nutrition at 20-25 kcal/kg/day (approximately 50% of predicted needs) to avoid harmful effects of early full feeding 3
• Target 80-100% of energy expenditure after day 3 once hemodynamic alterations resolve 1

Protein Requirements

• Deliver 1.3-1.5 g/kg ideal body weight/day of balanced amino acid mixture with adequate energy supply 1, 2
• Protein can be delivered progressively at 1.3 g/kg/day during critical illness 1
• Include 0.2-0.4 g/kg/day of L-glutamine (e.g., 0.3-0.6 g/kg/day alanyl-glutamine dipeptide) in amino acid solutions 1

Carbohydrate Management

• Minimum carbohydrate requirement is approximately 2 g/kg glucose per day 1
• Maximum glucose infusion rate should not exceed 5 mg/kg/min (approximately 400-700 g/day for 70 kg patient) to decrease risk of metabolic alterations 1

Lipid Requirements

• Lipids should be integral part of PN for energy and essential fatty acid provision 1
• Administer intravenous lipid emulsions at 0.7-1.5 g/kg over 12-24 hours 1
• Fish oil-enriched lipid emulsions probably decrease length of stay in critically ill patients 1

Micronutrients

• All PN prescriptions must include daily dose of multivitamins and trace elements 1

Administration Route

Central vs. Peripheral Access

• Central venous access is required for high osmolarity TPN mixtures (>850 mOsmol/L) designed to cover full nutritional needs 1, 2, 4
• Peripheral venous access may be used for low osmolarity mixtures (<850 mOsmol/L) providing partial nutrition 1, 3, 4
• If peripherally administered PN does not allow full provision of patient's needs, switch to central administration 1, 4

Formulation

• Use all-in-one bag system (Grade B) rather than separate containers to minimize administration errors and septic/metabolic complications 1

Critical Monitoring and Pitfalls

Glucose Control

• Maintain blood glucose between 4.5-10 mmol/L (81-180 mg/dL) 3, 2
• Hyperglycemia (glucose >10 mmol/L) contributes to death and infectious complications in critically ill patients 1, 2
• Avoid tight glycemic control (4.5-6.1 mmol/L) due to increased mortality and severe hypoglycemia risk (Grade A) 1
• Reduce glucose-based calories if blood sugar exceeds 180 mg/dL 3

Energy Deficit Prevention

• Negative energy balance is associated with increased infectious complications, prolonged mechanical ventilation, and longer ICU stays 1, 2
• Patients with total energy balance <10,000 kcal during entire ICU stay had mortality >85% 1

Overfeeding Avoidance

• Avoid hyperalimentation during acute phase as it increases mortality and complications 5
• Excessive calculated energy requirements (>25 kcal/kg/day) are risk factors for liver dysfunction 6

Infection Risk

• TPN increases infectious complications compared to EN, particularly in critically ill patients 7
• Liver dysfunction occurs in 30% of TPN patients vs. 18% of EN patients 6

Special Population: Sepsis/Septic Shock

• Provide 20-50% of nutrition support early, then increase gradually according to GI tolerance once hemodynamic alterations resolve 3