Critical illness triggers a hypermetabolic, catabolic state that rapidly breaks down muscle and depletes reserves. Evidence-based nutrition—preferably via the gut—can reduce complications and support recovery when started thoughtfully and monitored closely1.
Why Early Nutrition Matters
Guidelines recommend initiating enteral nutrition (EN) within the first 24–48 hours of ICU admission when the gut is functional. Early EN is associated with lower infectious complications and improved ICU outcomes compared with delayed feeding or exclusive IV fluids1, 2.
Energy: How Much to Feed?
- Indirect calorimetry is preferred to estimate energy needs in the ICU when available because prediction equations are often inaccurate in critical illness1.
- If calorimetry is not available, many protocols target ~25–30 kcal/kg/day after the initial stabilization phase, advancing from hypocaloric starts as tolerated1.
- For patients with obesity, hypocaloric (but high-protein) feeding is recommended to preserve lean tissue while avoiding overfeeding1.
Protein: Dose That Protects Lean Mass
Critical illness elevates protein turnover and losses. Many adults benefit from ~1.2–2.0 g/kg/day of protein, individualized by diagnosis, renal/hepatic status, and dialysis needs. In obesity, guidelines suggest ~2.0–2.5 g/kg/day based on ideal body weight when using hypocaloric strategies1.
Enteral vs Parenteral Nutrition
- Enteral nutrition (EN) is first-line when the GI tract is usable; consider post-pyloric access if aspiration risk or gastric intolerance persists despite standard measures2.
- Parenteral nutrition (PN) is indicated when EN is contraindicated or not meeting needs. In well-nourished patients, many protocols delay PN up to 7 days; in malnourished patients or those with inadequate EN, PN may be started earlier with careful monitoring1.
Glycemic Control
For most critically ill adults, a moderate target—maintaining blood glucose in the 140–180 mg/dL range—balances the risks of hyperglycemia with those of hypoglycemia from overly tight control3.
Micronutrients, Fluids, and Refeeding Risk
- Assess risk for refeeding syndrome in severely malnourished or long-NPO patients; start low and go slow with calories, supplement thiamine, and correct electrolytes (phosphorus, potassium, magnesium) proactively1.
- Critically ill patients often need tailored electrolyte and trace element strategies; monitor labs frequently, especially with renal replacement therapy or large fluid shifts2.
Feeding Intolerance: Practical Steps
- Use head-of-bed elevation, prokinetics when appropriate, and switch to post-pyloric feeding if gastric residuals and aspiration risk persist2.
- Consider peptide-based or lower-fat formulas for malabsorption; evaluate for bowel ischemia or uncontrolled shock where EN may be unsafe1.
Special Populations
- Renal replacement therapy: Higher protein losses through dialysis often push requirements upward; adjust electrolytes and fluids accordingly1.
- ARDS/ventilated patients: Avoid overfeeding CO₂-producing calories; consider energy from propofol when calculating totals2.
- Sepsis/major trauma/burns: Protein needs are typically on the high end of ranges; early EN remains preferred as perfusion allows1.
Sample ICU Feeding Workflow
- Screen nutrition risk on admission; place NG/OG tube if appropriate2.
- Start trophic or low-rate EN within 24–48 h if hemodynamically stable; advance as tolerated toward energy/protein targets1, 2.
- Monitor GI tolerance, fluid balance, electrolytes, glucose, nitrogen balance/urea trend; adjust formula and rate2.
- Bridge with PN if EN is contraindicated or insufficient despite optimization, factoring in nutrition status and risk1.
Frequently Asked Questions
When should we stop feeds for procedures?
Many bedside procedures do not require prolonged interruptions. Minimize NPO time and resume EN promptly when safe to avoid cumulative calorie/protein deficits2.
Do immunonutrition formulas help?
Specialized formulas (e.g., with omega-3s, arginine) have mixed evidence outside select surgical populations. Standard polymeric formulas meet needs in most medical ICU patients unless otherwise indicated1.
How fast should we advance feeds?
Advance progressively over 24–48 h as tolerated while watching hemodynamics and GI function; slower in high refeeding-risk patients with aggressive electrolyte repletion and thiamine support1.
References
- ASPEN/SCCM Guidelines for the Provision and Assessment of Nutrition Support Therapy in the Adult Critically Ill Patient. American Society for Parenteral and Enteral Nutrition & Society of Critical Care Medicine. Practice recommendations on timing, energy/protein targets, obesity strategies, and refeeding precautions. nutritioncare.org
- ESPEN Guidelines on Clinical Nutrition in the Intensive Care Unit. European Society for Clinical Nutrition and Metabolism. Includes early enteral nutrition, access route, intolerance management, and formula selection. espen.org
- American Diabetes Association/Endocrine Society statements on inpatient glycemic management: recommended target 140–180 mg/dL for most critically ill adults. diabetesjournals.org/care