Nutrition in the ICU Patient

Notes for MD Anaesthesiology Examination (10 Marks)

1. Introduction and Importance

• Accelerated protein breakdown and muscle wasting
• Insulin resistance and stress hyperglycemia
• Altered fat mobilization
• Increased energy demand with impaired utilization

2. Nutritional Risk Screening (Step 1 on ICU Admission)

NUTRIC Score (Nutrition Risk in the Critically Ill)

• Score ≥5 (without IL-6) or ≥6 (with IL-6) = high nutritional risk
• Indicates patients most likely to benefit from aggressive nutritional therapy

NRS-2002 (Nutritional Risk Screening 2002)

• Score ≥3 = nutritional risk; score ≥5 = high nutritional risk
• ICU patients with APACHE >10 score 3 points for disease severity automatically

3. Calculating Nutritional Requirements

3a. Energy Requirements

• Use a published predictive equation (Penn State, Mifflin-St Jeor) OR
• Simplistic weight-based equation: 12-25 kcal/kg actual body weight (ABW)/day during the first 7-10 days of ICU stay (ASPEN 2021)
• ESPEN 2023: Target ~20-25 kcal/kg/day in the recovery phase; avoid overfeeding in the acute phase

3b. Protein Requirements

• Standard range: 1.2-2.0 g/kg ABW/day (ASPEN 2016/2021; Mulholland 7e)
• May be higher in burns or polytrauma patients
• Obese patients (BMI >30): ≥2.0 g/kg ideal body weight (IBW)/day for BMI 30-40; up to 2.5 g/kg IBW/day for BMI ≥40
• Ongoing evaluation of protein adequacy is recommended
• The EFFORT Protein trial (Heyland et al., Lancet 2023) found higher protein dosing did not improve outcomes in all high-risk ICU patients - clinical judgment required

3c. Carbohydrates and Lipids

• Carbohydrates: primary energy substrate; avoid excess (promotes hyperglycemia, fatty liver)
• Lipids (IV): Mixed-oil or 100% soy-oil IV lipids are acceptable in PN patients; fish oil-containing lipids may be used (ASPEN 2021)
• Lipids provide the highest caloric density and are essential for fat-soluble vitamins and cell membrane integrity

4. Route of Nutrition Support

Priority Order (ASPEN/SCCM, ESPEN 2023):

1. Oral diet - preferred whenever the patient can eat safely
2. Enteral Nutrition (EN) - next preferred; use when GI tract functional
3. Parenteral Nutrition (PN) - reserve; use when EN not feasible or insufficient

Why Enteral Nutrition is Preferred:

• Maintains gut mucosal integrity and prevents bacterial translocation
• Preserves gut-associated lymphoid tissue (GALT)
• Maintains secretory IgA production
• Reduces infectious complications (meta-analysis: RR 0.64 for ICU infections vs. PN) - ESPEN 2023
• Avoids complications of PN (hyperglycemia, fatty liver, cholestasis, catheter-related sepsis)

5. Timing of Nutrition Support

Early Enteral Nutrition (EEN):

• Initiate EN within 24-48 hours of ICU admission in patients unable to maintain volitional intake (ASPEN/SCCM 2016; ESPEN 2023)
• EEN is associated with improved outcomes vs. delayed feeding
• Energy/protein goals should be achieved progressively over 48-72 hours - avoid sudden full target feeding to prevent refeeding syndrome

Parenteral Nutrition Timing:

• Low nutritional risk patients: Delay PN for 7 days if EN is not feasible; initiating PN before day 7-10 when EN is partially feasible does NOT improve outcomes and may be harmful (EPaNIC trial evidence)
• High nutritional risk patients (severely malnourished, GI tract non-functional for >5 days): Start PN as soon as possible after resuscitation
• Supplemental PN: Add PN only if EN fails to meet >60% of energy and protein requirements after 7-10 days of ICU stay

6. Enteral Nutrition: Practical Considerations

Route of Delivery:

• Gastric feeding (nasogastric tube): First-line; most patients tolerate this safely
• Post-pyloric feeding (nasojejunal tube): Use in patients with:
  • High aspiration risk
  • Gastric feeding intolerance despite prokinetics
  • Gastroparesis

Head of Bed Position:

• Elevate head to 30-45° to reduce aspiration risk

Managing Intolerance:

• Prokinetic agents: Metoclopramide (10 mg TDS) or Erythromycin (3-7 mg/kg/day)
• Use if gastric residual volumes (GRV) >500 mL/6 hours

Gastric Residual Volume (GRV) Monitoring:

• Routine GRV monitoring is no longer recommended (ASPEN 2016 bundle statement)
• Do NOT hold EN for GRV <500 mL in the absence of other signs of intolerance
• Avoid inappropriate cessation of EN

Enteral Feeding Protocols:

• Institutionalized volume-based or top-down multi-strategy protocols improve percentage of caloric goal achieved
• Minimize interruptions to EN delivery

Special Situations for EN Caution:

• Vasopressor support / septic shock: EN may be given cautiously after successful resuscitation; start at low rate (20-50% of target) to "open" the gut and advance gradually; bowel ischemia is a rare but serious risk
• Prone positioning: EN can be continued during prone ventilation
• ECMO (VV/VA): Initiate continuous intragastric EN at trophic rate (10-20 mL/h) within 24 hours; increase over 24-36 hours

7. Parenteral Nutrition (PN)

Indications:

• GI tract non-functional or inaccessible
• EN not tolerated despite optimization
• High nutritional risk with failure to achieve >60% of targets via EN after 7-10 days

Components of TPN:

• Dextrose (carbohydrate source) - maximum oxidation rate 4-5 mg/kg/min
• Amino acids (protein source) - 1.2-2.0 g/kg/day as standard
• Lipid emulsions - 20-30% of total calories; mixed-oil (soy/MCT/olive/fish) preferred
• Electrolytes: Na, K, Ca, Mg, Phosphate
• Vitamins and trace elements: Essential daily; Vitamin C, B complex, zinc, selenium, copper

Complications of PN:

• Hyperglycemia (most common)
• Fatty liver and cholestasis with long-term use
• Hypertriglyceridemia
• Catheter-related bloodstream infection (CRBSI)
• Metabolic derangements (electrolyte imbalance, refeeding syndrome)
• Gut atrophy and bacterial translocation

8. Immunonutrition and Special Substrates

Glutamine:

• Enteral glutamine in burns (>20% BSA): 0.3-0.5 g/kg/day for 10-15 days (ESPEN 2023, Grade B)
• IV glutamine in PN: NOT recommended routinely in ICU patients (evidence from REDOXS trial showed harm in multi-organ failure)
• Role remains as an essential conditionally indispensable amino acid in gut epithelial repair and immune function

Omega-3 Fatty Acids (EPA/DHA):

• Anti-inflammatory lipid mediators
• May be considered in ARDS patients (weak recommendation); routine use in general ICU not supported

Antioxidants (Selenium, Zinc, Vitamin C, E):

• Critically ill patients have depleted antioxidant reserves
• Adequate replacement doses are recommended; mega-dosing is not supported

Arginine-containing Immune-Modulating Formulas:

• Avoid in sepsis/septic shock (may worsen outcomes via excessive NO production)
• May be considered in elective surgical ICU patients

9. Glycemic Control in the ICU

Key Evidence:

• Van den Berghe et al. (2001): Intensive insulin therapy (IIT) targeting glucose 80-110 mg/dL reduced surgical ICU mortality by 42% (largely due to high exogenous glucose infusion in controls)
• NICE-SUGAR Trial (2009): Intensive control (81-108 mg/dL) increased 90-day mortality vs. conventional control (144-180 mg/dL); severe hypoglycemia: 6.8% vs. 0.5%

Current Recommendations (Multiple Guidelines, Barash's Clinical Anesthesia 9e):

• Target blood glucose ≤180 mg/dL in all critically ill patients
• Avoid hypoglycemia (<70 mg/dL) - independently associated with mortality
• Use IV insulin infusion protocols for tight-but-not-too-tight control
• Target 140-180 mg/dL is widely accepted (ACP 2011, Surviving Sepsis Campaign)

10. Refeeding Syndrome

• Severe hypophosphatemia (hallmark)
• Hypokalemia, hypomagnesemia
• Fluid shifts, cardiac arrhythmias, respiratory failure, seizures, neurological dysfunction

• Correct electrolytes (especially phosphate, potassium, magnesium) before initiating feeds
• Start nutrition at low rate (10-20 kcal/kg/day or ~50% target) and advance slowly over 4-7 days
• Monitor electrolytes daily for the first week
• Supplement thiamine (Vitamin B1) before and during refeeding

11. Monitoring Adequacy of Nutrition

12. Special ICU Populations

Summary: Key Numbers to Remember

References (for Exam Credit)

1. ASPEN/SCCM Guidelines 2016 - McClave SA et al. JPEN 2016;40(2):159-211
2. ASPEN Guidelines 2021 - Compher C et al. JPEN 2021 (Compher update)
3. ESPEN Practical Guidelines 2023 - Singer P, Blaser AR, Berger MM et al. Clinical Nutrition 2023;42:1671-1689
4. ASPEN EN Indications 2022 - Bechtold ML et al. JPEN 2022;46:1470-1496
5. NICE-SUGAR Trial - NEJM 2009;360:1283-1297
6. EFFORT Protein Trial - Heyland DK et al. Lancet 2023;401(10376):568-576
7. Barash Clinical Anesthesia 9e - Chapter 47 (Glycemic Goals in ICU)
8. Harrison's Principles of Internal Medicine 22e - Chapter on Critical Illness (Nutrition & Glycemic Control)
9. Mulholland & Greenfield's Surgery 7e - Chapter 3 (ICU Nutrition Bundle)