Nutrition in Critical Illness

Nutrition in Critical Illness: Metabolic Response & Assessment - Stress & Status

• Metabolic Response to Stress:
  • Hypermetabolism & severe catabolism.
  • ↑ Cortisol, glucagon, catecholamines; insulin resistance.
  • Cytokines (TNF-α, IL-1, IL-6) mediate.
  • Phases:
    • Ebb (24-48h): Hypometabolism. Goal: Resuscitation.
    • Flow: Hypermetabolism, ↑ catabolism, ↑ energy needs.
• Nutritional Status Assessment:
  • Clinical: Weight loss Hx, muscle wasting.
  • Biochemical:
    • Serum proteins (albumin, prealbumin): ↓ by inflammation, unreliable alone.
    • Nitrogen balance: $N_{balance} = (Protein_{intake}/6.25) - (UUN + 4)$. Aim positive.
  • Energy Expenditure:
    • Predictive equations: Often inaccurate.
    • RQ = $VCO_2 / VO_2$.
      • RQ: ~0.7 fat, ~0.8 protein, ~1.0 carb; >1.0 overfeeding.

⭐ Indirect calorimetry is the gold standard for determining energy expenditure in ICU patients, when available.

Nutrition in Critical Illness: Enteral Nutrition - Gut First Feeds

⭐ Early enteral nutrition (initiated within 24-48 hours of ICU admission) is preferred over delayed EN or parenteral nutrition in critically ill patients who can tolerate it.

• Principle: "If the gut works, use it!" - preserves gut mucosal barrier, prevents bacterial translocation.
• Timing: Initiate early, within 24-48h of ICU admission, if hemodynamically stable.
• Benefits: ↓ septic complications, ↓ MODS, ↓ ICU stay, cost-effective.
• Access Routes: Nasogastric (NG)/nasojejunal (NJ) short-term; PEG/PEJ for prolonged needs.
• Monitoring Tolerance:
  • Clinical: Abdominal distension, pain, bowel sounds, stool.
  • GRV: Check q4-6h; >500mL (or 200-500mL + symptoms) → hold, reassess, prokinetics.
• Complications: Aspiration (HOB 30-45°), diarrhea, tube malposition/clogging.

Nutrition in Critical Illness: Parenteral Nutrition - Veinous Victuals

• Parenteral Nutrition (PN): Intravenous administration of nutrients when the enteral route is contraindicated or insufficient.
• Indications:
  • Non-functional GI tract (e.g., prolonged ileus, obstruction, severe shock, high-output fistula).
  • Inability to achieve >60% of energy/protein requirements via EN by day 7-10.

  ⭐ If enteral nutrition is not feasible or sufficient, parenteral nutrition should be considered cautiously, typically after 7-10 days in patients at low nutritional risk, to avoid overfeeding and complications.

• Timing of Initiation:
  • Low nutritional risk: Consider if EN not feasible/sufficient by day 7-10.
  • High nutritional risk or severe malnutrition: Initiate early (within 24-48 hours) if EN is not possible.
• Access & Solutions:
  • Total PN (TPN): Via central venous catheter; allows hyperosmolar solutions for long-term needs.
  • Peripheral PN (PPN): Via peripheral vein; osmolarity limit <900 mOsm/L; for short-term use (<2 weeks).
• Major Complications:
  • Catheter-related: Infection (CRBSI), thrombosis, pneumothorax.
  • Metabolic: Hyperglycemia, refeeding syndrome, electrolyte disturbances, PN-Associated Liver Disease (PNALD).
• Monitoring: Blood glucose, electrolytes, LFTs, triglycerides.

Nutrition in Critical Illness: Monitoring & Complications - Watchful & Wise

• Vigilant Monitoring:
  • Clinical: GI tolerance (N/V/D), fluid status.
  • Biochemical: Glucose (target 140-180 mg/dL), electrolytes (PO4, K, Mg - daily if risk), TGs.
• Potential Complications:
  • Refeeding Syndrome: ⚠️ Severe ↓PO4, ↓K, ↓Mg (📌 P K Mg: Phosphate, Kalium, Magnesium). Risk in severely malnourished.
    • Initiate feeding low, advance slowly.
  • Overfeeding: Hyperglycemia, ↑CO2 production, hepatic steatosis.
  • Underfeeding: Weakness, poor healing, ↑infection risk.
  • GI intolerance: Diarrhea, high GRV.

⭐ Refeeding syndrome, characterized by severe hypophosphatemia, hypokalemia, and hypomagnesemia, is a critical complication to monitor for when initiating nutrition in severely malnourished patients.

High‑Yield Points - ⚡ Biggest Takeaways

• Early Enteral Nutrition (EN) within 24-48 hours is superior to Parenteral Nutrition (PN).
• Target calories: 25-30 kcal/kg/day; Target protein: 1.2-2.0 g/kg/day.
• Immunonutrition (e.g., arginine, glutamine) benefits select critically ill patients.
• Prevent Refeeding Syndrome: monitor for hypophosphatemia, hypokalemia, hypomagnesemia.
• Permissive underfeeding or trophic feeding is often an initial strategy.
• Gastric Residual Volume (GRV) monitoring is de-emphasized; focus on clinical intolerance.