What are the guidelines for parenteral nutrition (PN) in critically ill patients in the Intensive Care Unit (ICU)?

Guidelines for Parenteral Nutrition in ICU Patients

Parenteral nutrition (PN) should be initiated within 24-48 hours in critically ill ICU patients when enteral nutrition (EN) is contraindicated or insufficient, using a complete formulation tailored to the patient's metabolic needs. 1

When to Initiate Parenteral Nutrition

Primary Indications

• Start PN within 24-48 hours if the patient is not expected to resume normal nutrition within 3 days AND:
  • Enteral nutrition is contraindicated
  • Patient cannot tolerate enteral feeding 1
  • Patient is receiving less than targeted enteral feeding after 2 days 1

Specific Clinical Scenarios

• Contraindications to enteral feeding requiring early PN:
  • Uncontrolled shock
  • Uncontrolled hypoxemia and acidosis
  • Uncontrolled upper GI bleeding
  • Gastric aspirate >500 ml/6 hours
  • Bowel ischemia
  • Bowel obstruction
  • Abdominal compartment syndrome
  • High-output fistula without distal feeding access 1

Nutritional Requirements

Energy Requirements

• Initial phase (acute illness):
  • Aim for 25 kcal/kg/day, increasing to target over 2-3 days 1
  • Avoid exceeding 20-25 kcal/kg/day in the acute phase as this may worsen outcomes 1
  • Ideally, measure energy expenditure using indirect calorimetry 1

Macronutrient Composition

• Carbohydrates:

  • Minimum requirement: 2 g/kg glucose per day 1
  • Should constitute approximately 60% of non-protein energy 2
  • Maintain blood glucose <10 mmol/L to prevent infectious complications 1

• Lipids:

  • Should constitute approximately 40% of non-protein energy 2
  • Administer 0.7-1.5 g/kg over 12-24 hours 1
  • Use olive oil-based or fish oil-enriched lipid emulsions rather than pure soybean oil-based emulsions 1, 3

• Amino Acids:

  • Provide 1.3-1.5 g/kg ideal body weight/day 1
  • Include 0.2-0.4 g/kg/day of L-glutamine (0.3-0.6 g/kg/day alanyl-glutamine dipeptide) 1

Micronutrients

• All PN prescriptions should include daily doses of multivitamins and trace elements 1
• Consider evaluation of micronutrient levels after 5-7 days in patients at risk of deficiencies (e.g., those on CRRT) 1

Administration Route

• Central venous access is typically required for high osmolarity PN formulations designed to fully meet nutritional needs 1
• Peripheral venous access may be used for lower osmolarity mixtures (<850 mOsmol/L) intended to supplement nutrition 1

Implementation and Monitoring

Starting and Advancing PN

• Begin with low-dose PN in the early phase of critical illness (first 1-2 days) 1
• Gradually increase to target over 2-3 days while monitoring metabolic tolerance 1
• Avoid overfeeding, which can be as detrimental as underfeeding 1

Glucose Control

• Implement strict glycemic control protocols
• Maintain blood glucose <10 mmol/L 1
• Be aware of increased risk of hypoglycemia with tight glucose control (4.5-6.1 mmol/L) 1

Infection Prevention

• Implement insertion and care bundles for central venous access devices 3
• Follow "near zero" catheter-related bloodstream infection protocols 3

Combined Nutritional Support

• When EN is possible but insufficient, consider supplemental PN after 2 days of inadequate enteral intake 1, 4
• Recent evidence suggests that properly managed PN (avoiding overfeeding and with good glycemic control) does not increase mortality or infectious complications compared to EN 3, 4, 5, 6

Special Considerations

• In patients with severe undernutrition, aim for 25-30 kcal/kg/day and consider supplemental PN if enteral targets cannot be reached 1
• During recovery phase, increase energy provision to 25-30 kcal/kg/day 1
• Consider using nutrition support teams and protocols to decrease PN-related complications 3

Common Pitfalls to Avoid

1. Delaying nutritional support - Starvation or underfeeding in ICU patients is associated with increased morbidity and mortality 1
2. Overfeeding - Can be as harmful as underfeeding, especially in the acute phase of illness 1
3. Poor glycemic control - Hyperglycemia contributes to increased mortality and infectious complications 1
4. Inadequate monitoring - Regular assessment of metabolic parameters and nutritional status is essential 1
5. Focusing exclusively on EN - When EN is insufficient, supplemental PN should be considered to prevent nutritional deficits 4, 6

By following these guidelines, PN can be safely and effectively administered to critically ill patients, with the goal of improving clinical outcomes by preventing or treating malnutrition while minimizing complications.