What are the guidelines for enteral (enteral nutrition) vs parenteral (parenteral nutrition) nutrition in Intensive Care Unit (ICU) patients?

Guidelines for Enteral vs Parenteral Nutrition in ICU Patients

Primary Recommendation

Enteral nutrition (EN) should be initiated within 24-48 hours of ICU admission in all hemodynamically stable patients with a functioning gastrointestinal tract, as it is the preferred route that reduces infectious complications and shortens ICU length of stay compared to parenteral nutrition (PN). 1, 2

When to Initiate Nutritional Support

• All ICU patients not expected to resume full oral diet within 3 days should receive nutritional support 1, 2
• Early EN (within 24-48 hours) should be started in hemodynamically stable patients with functioning GI tracts 1
• Start EN at low rates (10-20 ml/h) and increase gradually while monitoring for tolerance 1

Evidence Supporting Enteral Over Parenteral Nutrition

EN significantly reduces infectious complications compared to PN (RR 0.64,95% CI 0.48-0.87) and decreases ICU length of stay (mean difference -0.80 days) 2, 3

• Early EN reduces infectious complications by 50% compared to early PN (RR 0.50, CI 0.37-0.67) 2
• EN leads to shorter ICU stays and hospital stays compared to TPN 2
• No mortality difference exists between EN and PN (RR 1.04,95% CI 0.82-1.33), making infectious complications and ICU stay the key differentiating outcomes 3

Energy and Protein Targets

Acute Phase (First 3-4 Days)

• Provide 20-25 kcal/kg/day during the acute phase to avoid overfeeding, which worsens outcomes 1, 4
• Start with low-dose protein (<0.8 g/kg/day) in the first 1-2 days 1

Recovery Phase

• Increase to 25-30 kcal/kg/day once patients stabilize 1, 4
• Progress protein to ≥1.2 g/kg/day as patients stabilize 1
• Indirect calorimetry is recommended to measure actual energy expenditure after stabilization 1, 4

When Parenteral Nutrition is Appropriate

PN should be considered when EN is contraindicated, not feasible, or fails to meet nutritional requirements after 2-3 days 1, 2

Specific Indications for PN:

• Supplementary PN should be added after 2-3 days if EN fails to reach target intake 1, 2
• PN can be initiated within 24-48 hours if EN is contraindicated or not tolerated 1, 4
• Recent evidence shows PN can be given safely without increased risk when EN is not feasible, resulting in similar outcomes when isocaloric 1

Important Caveat About PN Safety:

The reduction in infectious complications with EN versus PN is most pronounced when PN groups received significantly more calories (RR 0.55,95% CI 0.37-0.82), while no difference exists when caloric intake is similar between groups (RR 0.94,95% CI 0.80-1.10) 3. This suggests the harm from PN may be related to overfeeding rather than the route itself 5, 3.

Absolute Contraindications to Early EN

Delay EN in the following conditions 1:

• Uncontrolled shock or hemodynamic instability
• 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

Route of EN Administration

• No significant difference exists between gastric and jejunal feeding in most ICU patients 1, 2
• Gastric feeding is acceptable as the initial approach in most patients 1
• Consider prokinetic agents (metoclopramide or erythromycin) for high gastric residuals 1

Formula Selection

• Whole protein formulas are appropriate for most patients, as no clinical advantage exists for peptide-based formulas 1, 2
• Immune-modulating formulas are NOT recommended in severe sepsis (APACHE II >15) and may be harmful 1
• Immune-modulating formulas may benefit patients with mild sepsis (APACHE II <15) or after GI surgery 1

Critical Pitfalls to Avoid

Overfeeding

Providing >25 kcal/kg/day during the acute phase is associated with worse outcomes 1, 4. This is particularly problematic with PN where full caloric targets are easier to achieve 5, 3.

Delayed Initiation

Delaying nutritional support beyond 48 hours in appropriate candidates increases morbidity 1, 2. However, this must be balanced against the contraindications listed above.

Abandoning EN Prematurely

High gastric residuals should prompt intervention (prokinetics, post-pyloric feeding) rather than abandonment of EN 1, 2. Continue EN at slow rates while addressing intolerance.

Ignoring Protein Targets

Inadequate protein provision leads to increased muscle wasting, yet protein is often neglected when focusing solely on caloric targets 1, 4.

Refeeding Syndrome

Monitor electrolytes (especially phosphorus, potassium, magnesium) closely when initiating nutrition in malnourished patients 2, 4.

Practical Algorithm for ICU Nutrition

1. Assess within 24 hours: Is the patient hemodynamically stable with functioning GI tract?

   • Yes → Initiate EN at 10-20 ml/h 1
   • No → Address contraindications; consider low-dose PN if EN contraindicated 1

2. Target during acute phase (Days 1-3): 20-25 kcal/kg/day, <0.8 g/kg/day protein 1

3. Assess at Day 2-3: Is EN meeting 50-70% of targets?

   • Yes → Continue advancing EN 1, 2
   • No → Add supplementary PN 1

4. Recovery phase (Day 4+): Increase to 25-30 kcal/kg/day, ≥1.2 g/kg/day protein 1

5. Use indirect calorimetry when available to guide targets after stabilization 1, 4