Intensive Care Medicine

Enteral Nutrition in Critical Care

Enteral nutrition (EN) is the preferred method of nutritional support in critically ill patients with a functioning gast... CICM Fellowship Written, CICM Fellow

Updated 25 Jan 2026
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Enteral Nutrition in Critical Care

Clinical Overview

Enteral nutrition (EN) is the preferred method of nutritional support in critically ill patients with a functioning gastrointestinal tract. Early initiation of EN within 24-48 hours of ICU admission is associated with maintenance of gut mucosal integrity, reduced infectious complications, shorter ICU length of stay, and lower healthcare costs compared to delayed feeding or parenteral nutrition. [1,2,3]

Despite these benefits, EN is frequently underprescribed or delayed in ICU settings, with studies showing that critically ill patients receive only 50-60% of their prescribed energy targets. [4,5] Barriers include perceived contraindications, feed intolerance, procedural interruptions, and clinician uncertainty regarding optimal timing and feeding strategies.

The Australian and New Zealand Intensive Care Society (ANZICS) Clinical Trials Group has been instrumental in generating high-quality evidence regarding EN practices, including landmark trials on timing (EPaNIC), volume (EDEN, EAT-ICU), and monitoring strategies (NUTRIREA-2). [6,7,8,9]

Key Concepts

Early EN Rationale

The gut plays a central role in the systemic inflammatory response and multi-organ dysfunction in critical illness. Enteral feeding helps maintain:

1. Gut Mucosal Barrier Integrity

  • Intestinal epithelial cells derive 60-70% of their energy from luminal nutrients (glutamine, short-chain fatty acids)
  • Absence of enteral feeding for \u003e48 hours leads to villous atrophy, increased intestinal permeability, and bacterial translocation [10,11]
  • EN maintains tight junction integrity and reduces apoptosis of enterocytes [12]

2. Gut-Associated Lymphoid Tissue (GALT) Function

  • GALT represents 70% of the immune system
  • Enteral feeding maintains secretory IgA production and mucosal immunity [13]
  • Preservation of commensal gut microbiota reduces pathogenic bacterial overgrowth [14]

3. Metabolic and Clinical Outcomes

  • Reduced infectious complications: Meta-analysis of 15 trials (n=2,652) showed EN vs PN reduced infection risk (RR 0.64, 95% CI 0.52-0.78) [15]
  • Cost savings: EN costs 10-20% of PN costs in most healthcare systems [16]
  • Lower glycemic variability compared to PN, reducing insulin requirements [17]

Timing of Enteral Nutrition

Early vs Delayed Feeding

Early EN Definition: Initiation within 24-48 hours of ICU admission or hemodynamic stabilization [18]

Evidence for Early EN:

  • NUTRIREA-1 (2011): Early EN (within 24h) vs early PN in acute lung injury - no difference in ventilator-free days, but trend toward reduced infections with EN (p=0.051) [19]
  • CALORIES (2014): Early EN vs early PN in critically ill adults - no difference in 30-day mortality, but lower bloodstream infections with EN (2.8% vs 6.8%, p\u003c0.001) [20]

Cautions with Very Early High-Dose Feeding:

  • EPaNIC Trial (2011): Late PN supplementation (after day 8) vs early PN (within 48h) to achieve caloric targets showed faster recovery and fewer infections with late PN approach [21]
  • Interpretation: Early aggressive caloric delivery via PN may be harmful; moderate early EN remains standard practice
  • EAT-ICU Trial (2024): Early goal-directed EN vs standard care showed no mortality benefit and higher GI complications (diarrhea, vomiting) with aggressive approach [9]

Current Consensus (ESPEN 2019, ASPEN 2016, ANZICS 2020): [22,23,24]

  • Initiate EN within 24-48 hours in hemodynamically stable patients
  • Avoid aggressive early PN supplementation
  • Accept energy deficits in the first 3-5 days (permissive underfeeding)

Route Selection

Nasogastric (NG) vs Nasojejunal (NJ) Feeding

Nasogastric Feeding:

  • Advantages: Easier insertion, no endoscopy/fluoroscopy required, allows gastric acid sterilization of feed
  • Disadvantages: Higher aspiration risk, delayed by gastroparesis (30-50% of ICU patients) [25]

Post-Pyloric (Nasojejunal/Nasoduodenal) Feeding:

  • Indications:

    • Recurrent aspiration or high aspiration risk
    • Gastroparesis refractory to prokinetics
    • Gastric outlet obstruction
    • Acute pancreatitis [26]
    • Post-esophagectomy, gastrectomy

  • Evidence:

    • "Meta-analysis (11 RCTs, n=1,438): Post-pyloric vs gastric feeding reduced pneumonia (RR 0.65, 95% CI 0.51-0.84) but no mortality benefit [27]"
    • Requires endoscopy, fluoroscopy, or electromagnetic-guided placement [28]
    • Higher success rate with prokinetic pre-treatment (metoclopramide 10 mg IV) [29]

ANZICS Practice: Gastric feeding is first-line; post-pyloric feeding reserved for documented feed intolerance or high aspiration risk [24]

Percutaneous Endoscopic Gastrostomy (PEG) and Jejunostomy (PEJ)

Indications for Long-Term Access (\u003e4-6 weeks):

  • Prolonged ventilation
  • Neurological dysphagia (stroke, TBI, neuromuscular disease)
  • Head and neck cancers
  • Anticipated long-term nutritional support

PEG Placement:

  • Contraindications: Coagulopathy (INR \u003e1.5, platelets \u003c50×10⁹/L), ascites, peritonitis, gastric varices, gastric outlet obstruction
  • Complications: Buried bumper syndrome (1-3%), site infection (5-10%), bleeding (\u003c1%) [30]

PEJ (Percutaneous Endoscopic Jejunostomy):

  • Used when gastric access contraindicated (gastroparesis, gastric cancer, recurrent aspiration)
  • Can be placed surgically (intra-operative) or endoscopically (direct PEJ or PEG-J conversion)
  • Requires continuous feeding (jejunum cannot accommodate bolus volumes)

Contraindications to Enteral Nutrition

Absolute Contraindications

  1. Bowel Ischemia or Infarction

    • Feeding increases metabolic demand and worsens ischemia
    • High mortality if EN initiated pre-resuscitation [31]

  2. Bowel Obstruction

    • Mechanical obstruction (tumor, adhesions, volvulus)
    • Feeding exacerbates distension and risk of perforation

  3. High-Output Proximal Small Bowel Fistula

    • Fistula output \u003e500 mL/day increases with EN
    • PN preferred to allow bowel rest and fistula closure [32]

  4. Severe Gastrointestinal Hemorrhage

    • Active upper or lower GI bleeding requiring resuscitation
    • EN can be cautiously restarted once bleeding controlled

Relative Contraindications (Require Careful Assessment)

  1. Hemodynamic Instability

    • Uncontrolled shock with escalating vasopressor requirements (norepinephrine \u003e0.5 mcg/kg/min)
    • Non-occlusive mesenteric ischemia (NOMI) risk: 0.3-3% in ICU patients on vasopressors [33]
    • Approach: Delay EN until hemodynamic stabilization; consider trophic feeding (10-20 mL/h) once stable [34]

  2. Severe Acute Pancreatitis

    • EN is preferred over PN in acute pancreatitis (reduces infections, organ failure) [35,36]
    • Contraindicated only if: ileus, abdominal compartment syndrome, bowel ischemia
    • Route: Nasojejunal preferred over nasogastric (avoids stimulation of pancreatic secretion), though recent evidence suggests NG may be safe [37]

  3. Abdominal Compartment Syndrome (ACS)

    • Intra-abdominal pressure (IAP) \u003e20 mmHg with organ dysfunction
    • EN increases IAP by 2-4 mmHg; may worsen ACS [38]
    • Resume EN after decompression (laparotomy, percutaneous drainage)

  4. Short Bowel Syndrome

    • Residual small bowel \u003c100 cm or no colon
    • EN may be insufficient; often requires supplemental PN

Enteral Nutrition Formulas

1. Polymeric (Standard) Formulas

Composition:

  • Intact proteins (casein, whey, soy)
  • Long-chain triglycerides (LCT)
  • Complex carbohydrates (maltodextrin)
  • 1.0-1.5 kcal/mL

Indications: First-line for patients with normal GI function

Examples (Australian Products):

  • Osmolite (1.0 kcal/mL, 300 mOsm/kg)
  • Isosource Standard (1.2 kcal/mL)
  • Nutrison Standard (1.0 kcal/mL)

Advantages: Lower cost, physiologic nutrient composition

Disadvantages: Requires intact digestive and absorptive function

2. Elemental (Peptide-Based) Formulas

Composition:

  • Hydrolyzed proteins (di- and tri-peptides)
  • Medium-chain triglycerides (MCT) 30-60%
  • Simple sugars
  • 1.0 kcal/mL, high osmolality (400-600 mOsm/kg)

Indications:

  • Malabsorption (short bowel, pancreatic insufficiency)
  • Prolonged bowel rest (\u003e7 days) with villous atrophy
  • Severe diarrhea refractory to standard formula

Examples:

  • Peptamen (1.0 kcal/mL, 40% MCT)
  • Vital (1.0 kcal/mL, elemental)

Evidence: Limited benefit in critically ill patients with normal GI function; more expensive (3-5× cost of polymeric) [39]

3. Immune-Modulating Formulas (Immunonutrition)

Composition:

  • Enriched with arginine, glutamine, omega-3 fatty acids (EPA/DHA), nucleotides, antioxidants (vitamins C, E, selenium)

Proposed Mechanisms:

  • Arginine: Enhances T-cell function, nitric oxide production
  • Glutamine: Enterocyte fuel, maintains gut barrier
  • Omega-3 fatty acids: Anti-inflammatory eicosanoids (↓ prostaglandin E2, ↓ leukotriene B4)

Evidence in Critical Care:

  • Meta-analysis (2013): Immunonutrition in surgical ICU patients reduced infections (RR 0.59) and length of stay (−2.5 days), no mortality benefit [40]
  • Sepsis: Potential harm with high-dose arginine (increased mortality in SIGNET trial) [41]
  • ARDS: Omega-3 supplementation in OMEGA trial showed no benefit (stopped early for futility) [42]

Current Recommendations (ESPEN 2019): [22]

  • Consider in major elective surgery (esophagectomy, pancreaticoduodenectomy)
  • Avoid in severe sepsis and septic shock
  • Not routinely recommended in general ICU population

Australian Products: Supportan (omega-3 enriched), Impact (arginine-enriched)

4. Disease-Specific Formulas

High-Protein Formulas:

  • 20-25% protein (vs 15-18% in standard)
  • Indications: Burns, trauma, ICU-acquired weakness, sarcopenia
  • Examples: Nutrison Protein Plus (20% protein), Isosource Protein (22% protein)

Renal Formulas:

  • Low protein (6-8%), low potassium, low phosphate
  • Indications: AKI/CKD without RRT
  • Caution: May worsen protein-energy malnutrition; consider only if severe electrolyte derangements

Diabetic Formulas:

  • Low carbohydrate (30-40%), high fat, high fiber
  • May improve glycemic control (modest effect: ↓ glucose by 0.5-1.0 mmol/L) [43]
  • Examples: Glucerna, Nutrison Advanced Diason

Respiratory Formulas:

  • High fat (50-55%), low carbohydrate (28-30%) to reduce CO₂ production (↓ RQ from 1.0 to 0.8)
  • Limited evidence for benefit in mechanically ventilated patients [44]
  • Examples: Oxepa (also omega-3 enriched), Pulmocare

Delivery Methods

Continuous Infusion

Protocol:

  • Starting rate: 10-25 mL/h
  • Advance by 10-25 mL/h every 4-8 hours as tolerated
  • Target rate: Typically 60-100 mL/h to meet energy requirements

Advantages:

  • Better tolerance in critically ill patients
  • Reduced metabolic stress (smaller glycemic excursions)
  • Mandatory for post-pyloric feeding (jejunum cannot accommodate bolus)

Disadvantages:

  • Requires infusion pump
  • Continuous feed interruptions for procedures, physiotherapy
  • Less physiologic (no fasting-fed cycle)

Bolus Feeding

Protocol:

  • 200-400 mL administered over 15-30 minutes, 4-6 times daily
  • Only via gastric route

Advantages:

  • More physiologic (mimics normal eating pattern)
  • Easier for ward-based care, home EN
  • Allows mobilization without pump

Disadvantages:

  • Higher aspiration risk
  • Greater GI intolerance (bloating, cramping, diarrhea)
  • Contraindicated in gastroparesis, high aspiration risk, post-pyloric feeding

Evidence: No difference in nutritional outcomes between continuous and bolus gastric feeding in stable ICU patients, but bolus associated with higher intolerance [45]

ANZICS Practice: Continuous infusion is standard in ICU; bolus feeding reserved for stable ward patients transitioning to oral intake

Feeding Protocols and Monitoring

Volume-Based Feeding Protocols

Goal: Deliver 80-100% of estimated energy requirements by day 3-5

Energy Targets:

  • Predictive equations (Schofield, Harris-Benedict, Penn State): Often overestimate in critically ill (25-30 kcal/kg/day typical)
  • Indirect calorimetry (IC): Gold standard for measuring resting energy expenditure (REE), but limited availability in Australia/NZ [46]
  • Pragmatic approach: 20-25 kcal/kg ideal body weight (IBW) for first week, then 25-30 kcal/kg [47]

Protein Targets:

  • 1.2-1.5 g/kg IBW in most critically ill patients
  • 1.5-2.0 g/kg in burns, trauma, sepsis with ongoing catabolism [48]
  • 2.0-2.5 g/kg in burns \u003e20% TBSA [49]

Gastric Residual Volume (GRV) Monitoring

Traditional Practice:

  • Measure GRV every 4-6 hours
  • Hold feeds if GRV \u003e200-250 mL
  • Rationale: Presumed marker of aspiration risk and feed intolerance

NUTRIREA-2 Trial (2013): [8]

  • Design: 452 ICU patients randomized to GRV monitoring (feeds held if \u003e250 mL) vs no GRV monitoring
  • Results:
    • "No difference in ventilator-associated pneumonia (VAP): 16.7% vs 16.3%"
    • No difference in aspiration, ICU mortality, or length of stay
    • "No GRV group received more EN: 1,534 vs 1,284 kcal/day (p\u003c0.001)"

Interpretation: Routine GRV monitoring is not necessary and reduces EN delivery without improving safety [50]

Current Guidelines (ESPEN 2019, ASPEN 2016): [22,23]

  • Do not routinely monitor GRV
  • If monitored, hold feeds only if GRV \u003e500 mL and clinical signs of intolerance (vomiting, abdominal distension, pain)
  • GRV \u003c500 mL alone is not a reason to stop EN

ANZICS Practice (2020): [24]

  • GRV monitoring not recommended in most ICUs
  • Focus on clinical assessment (abdominal exam, vomiting, aspiration events)

Complications of Enteral Nutrition

1. Aspiration Pneumonitis and Pneumonia

Incidence: 1-10% of ICU patients receiving EN [51]

Risk Factors:

  • Supine positioning (head of bed \u003c30°)
  • Depressed level of consciousness (GCS \u003c9)
  • Impaired gag reflex, dysphagia
  • Large-bore NG tube (prevents complete glottic closure)
  • Gastric feeding in gastroparesis
  • High GRV (\u003e500 mL) with vomiting [52]

Prevention:

  • Elevate head of bed to 30-45°: Reduces aspiration risk by 50-70% [53]
  • Continuous feeding rather than bolus
  • Post-pyloric feeding in high-risk patients (meta-analysis: RR 0.65 for pneumonia) [27]
  • Prokinetic agents: Metoclopramide 10 mg IV q6h or erythromycin 250 mg IV q6h
  • Blue dye testing: Abandoned due to lack of sensitivity and reports of toxicity [54]

Diagnosis:

  • Clinical (fever, purulent secretions, infiltrate on CXR)
  • Difficult to distinguish from VAP in intubated patients
  • Glucose testing of tracheal aspirate: Unreliable (sensitivity 30-50%) [55]

Management:

  • Stop EN temporarily
  • Ensure head elevation, suction oropharynx
  • Bronchoscopy if large-volume aspiration
  • Antibiotics as per VAP guidelines (cover Gram-negative, MRSA if risk factors)
  • Consider post-pyloric feeding once resolved

2. Diarrhea

Definition: \u003e3 loose stools per day or \u003e500 mL/day liquid stool [56]

Incidence: 20-68% of ICU patients receiving EN [57]

Causes:

A. Medication-Related (Most Common):

  • Antibiotics: Alter gut microbiome, reduce SCFA production
  • Sorbitol-containing medications: Liquid formulations (elixirs, suspensions)
  • Magnesium: Antacids, laxatives
  • Prokinetics: Metoclopramide, erythromycin

B. Infectious:

  • Clostridioides difficile infection (CDI): 10-20% of ICU diarrhea [58]
    • Diagnose with stool PCR or toxin assay
    • Treat with oral vancomycin 125 mg q6h or fidaxomicin 200 mg BD
  • Viral (Norovirus, Rotavirus in immunocompromised)

C. Formula-Related:

  • High osmolality: Elemental formulas (400-600 mOsm/kg) vs polymeric (300 mOsm/kg)
  • Bolus feeding: Rapid gastric distension
  • Lactose intolerance: Rare (most formulas lactose-free)
  • Fat malabsorption: Consider MCT-based formula

D. Bowel Pathology:

  • Fecal impaction with overflow: Digital rectal exam essential
  • Inflammatory bowel disease (IBD) flare
  • Ischemic colitis (especially if on vasopressors)

Management:

  1. Review medications: Discontinue unnecessary antibiotics, sorbitol-containing drugs
  2. Test for C. difficile: Stool PCR if diarrhea \u003e3 days or risk factors (antibiotics, PPIs, age \u003e65)
  3. Modify EN regimen:
    • Reduce infusion rate by 50% and gradually re-escalate
    • Switch to peptide-based formula if malabsorption suspected
    • Add soluble fiber (guar gum, pectin): May reduce diarrhea by bulking stool [59]
  4. Anti-diarrheal agents:
    • Loperamide: 2-4 mg q6h PRN (avoid if C. difficile positive)
    • Probiotics: Insufficient evidence in ICU setting; potential risk in immunocompromised [60]

Do NOT stop EN unless severe diarrhea (e.g., \u003e2 L/day) causing metabolic derangement or perianal skin breakdown

3. Tube Displacement and Malposition

Types:

A. External Displacement (10-60% of tubes):

  • Patient-induced (agitation, delirium)
  • Coughing, vomiting
  • Accidental removal during repositioning, suctioning

Prevention:

  • Secure tube with adhesive (not tape loops that allow sliding)
  • Nasal bridles: Secure tube via trans-septal suture; reduces dislodgement by 50% [61]
  • Mark exit site at naris and document length
  • Sedate/restrain if severe agitation

B. Internal Migration:

  • Gastric tube migrates to duodenum/jejunum: May cause feed intolerance (jejunum cannot handle large volumes)
  • Post-pyloric tube curls back into stomach: Defeats purpose; check position if GRV suddenly high

C. Malposition on Insertion:

  • Tracheobronchial placement: 1-2% of blind insertions [62]
    • "Risk factors: Altered consciousness, absent gag reflex, supine position"
    • Can cause pneumothorax, pneumonia, death if feeding initiated
  • Esophageal placement: Feed reflux and aspiration risk

Verification of Position:

  1. Chest X-ray (Gold Standard):
    • Confirm tube tip in stomach (below diaphragm) or post-pyloric (beyond duodenojejunal flexure at L2)
    • Mandatory before initiating feeding if blind insertion
  2. pH Testing: Gastric aspirate pH \u003c5 (high sensitivity 95%, but low specificity - many ICU patients on PPIs)
  3. "Whoosh test": Auscultation over epigastrium while injecting air - Unreliable, should not be used [63]
  4. Capnography: CO₂ detection if tube in airway (emerging technique)

4. Bloating and Abdominal Distension

Causes:

  • Gastroparesis: 30-50% of ICU patients [25]
  • Ileus: Post-operative, sepsis, electrolyte imbalance (hypokalemia, hypomagnesemia)
  • Constipation/fecal impaction: Opioids, immobility
  • Bowel obstruction: Adhesions, tumor
  • Intra-abdominal pathology: Ascites, pancreatitis, ischemic colitis

Assessment:

  • Clinical exam: Abdominal distension, pain, tympany, absent bowel sounds
  • Abdominal X-ray: Dilated bowel loops, air-fluid levels
  • CT abdomen: If concern for obstruction, ischemia, or perforation
  • Intra-abdominal pressure (IAP) monitoring: Bladder pressure via Foley catheter (normal \u003c12 mmHg)

Management:

  1. Hold EN temporarily if severe distension (IAP \u003e15 mmHg or clinical concern for ischemia)
  2. NG decompression: Switch feeding tube to free drainage
  3. Prokinetics:
    • Metoclopramide 10 mg IV q6h (max 5 days - extrapyramidal side effects)
    • Erythromycin 250 mg IV q6h (tachyphylaxis after 3-5 days)
  4. Laxatives: Senna, lactulose, macrogol (Movicol) for constipation
  5. Reduce feeding rate and gradually re-escalate once distension resolves
  6. Consider post-pyloric feeding if gastroparesis persists

5. Refeeding Syndrome

Definition: Severe electrolyte and fluid shifts occurring when nutrition is reintroduced after prolonged starvation [64]

Pathophysiology:

  • Prolonged fasting: Cellular depletion of phosphate, potassium, magnesium (though serum levels may appear normal)
  • Refeeding: Insulin surge drives glucose, phosphate, potassium, magnesium intracellularly
  • Hypophosphatemia (hallmark): Causes respiratory failure (diaphragm weakness), cardiac failure, hemolysis, rhabdomyolysis, seizures

Risk Factors (NICE Criteria): [65]

  • High risk if 1 or more of:
    • BMI \u003c16 kg/m²
    • Unintentional weight loss \u003e15% in 3-6 months
    • Little or no nutritional intake for \u003e10 days
    • Low potassium, phosphate, or magnesium before feeding
  • Moderate risk if 2 or more of:
    • BMI \u003c18.5 kg/m²
    • Unintentional weight loss \u003e10% in 3-6 months
    • Little or no intake for \u003e5 days
    • History of alcohol abuse, insulin, chemotherapy, antacids, diuretics

Prevention:

  1. Identify high-risk patients: Nutritional assessment at ICU admission
  2. Correct deficits pre-feeding:
    • Thiamine 200-300 mg IV daily × 3 days (prevents Wernicke's encephalopathy)
    • Phosphate, potassium, magnesium supplementation
  3. "Start low, go slow":
    • Initial feeding: 10-20 kcal/kg/day (50% of target)
    • Advance by 25% every 2-3 days if electrolytes stable
  4. Monitor electrolytes: Daily (or more frequently) for first 5-7 days
    • Phosphate \u003c0.65 mmol/L: Replace IV (see below)
    • Potassium \u003c3.5 mmol/L: Replace IV
    • Magnesium \u003c0.7 mmol/L: Replace IV

Treatment of Refeeding Hypophosphatemia:

  • Mild (0.65-0.8 mmol/L): Oral sodium phosphate 2-4 mmol PO TDS
  • Moderate (0.4-0.65 mmol/L): IV sodium phosphate 0.3-0.6 mmol/kg over 12-24 hours
  • Severe (\u003c0.4 mmol/L or symptomatic): IV sodium phosphate 0.8 mmol/kg over 12-24 hours, monitor hourly

Gastroparesis Management

Definition: Delayed gastric emptying without mechanical obstruction [25]

Incidence in ICU: 30-50% of mechanically ventilated patients

Risk Factors:

  • Critical illness (sepsis, multi-organ failure)
  • Sedation (opioids, propofol, benzodiazepines)
  • Hyperglycemia (\u003e10 mmol/L delays gastric emptying)
  • Intra-abdominal pathology (pancreatitis, post-operative ileus)
  • Medications: Anticholinergics, vasopressors (high-dose)

Diagnosis:

  • Clinical: Vomiting, high GRV (\u003e250 mL), abdominal distension
  • Paracetamol absorption test: Oral/NG paracetamol 1 g, measure serum level at 60 min (level \u003c10 mg/L suggests delayed emptying)
  • Gastric emptying scintigraphy (GES): Gold standard, rarely feasible in ICU

Prokinetic Agents

1. Metoclopramide (Maxolon, Reglan)

  • Mechanism: D2 antagonist, 5-HT4 agonist; increases LES tone, gastric contractions, pyloric relaxation
  • Dose: 10 mg IV q6h (can increase to 20 mg q6h)
  • Efficacy: Increases gastric emptying by 20-30%; variable effect on EN tolerance [66]
  • Side Effects:
    • "Extrapyramidal symptoms (EPS): Acute dystonia, tardive dyskinesia (5-10% if used \u003e3 months)"
    • QT prolongation (rare)
    • "Contraindicated: Bowel obstruction, pheochromocytoma, Parkinson's disease"
  • Australian TGA Warning: Limit use to \u003c5 days due to EPS risk

2. Erythromycin (Erythrocin)

  • Mechanism: Motilin receptor agonist; induces gastric phase III migrating motor complex (MMC)
  • Dose: 250 mg IV q6h (or 500 mg IV BD)
  • Efficacy: More effective than metoclopramide (increases emptying by 40-50%) [67]
  • Side Effects:
    • "Tachyphylaxis: Loss of effect after 3-5 days due to motilin receptor downregulation"
    • QT prolongation (monitor ECG)
    • "Drug interactions: CYP3A4 inhibitor (increases levels of midazolam, fentanyl, warfarin)"
    • "Bacterial resistance: Avoid prolonged use as antibiotic"
  • Use: Short-term (3-5 days) to facilitate post-pyloric tube placement

3. Combination Therapy:

  • Metoclopramide + erythromycin may have synergistic effect [68]
  • Use sequentially or together in refractory gastroparesis

4. Emerging Agents (Not Widely Available in Australia):

  • Prucalopride (Resolor): 5-HT4 agonist, approved for chronic constipation; limited ICU data
  • Ghrelin agonists (relamorelin): Phase II trials in gastroparesis

Post-Pyloric Feeding

When to Consider:

  • Persistent gastroparesis despite prokinetics
  • Recurrent aspiration events
  • High GRV (\u003e500 mL) with clinical intolerance

Placement Techniques:

  1. Endoscopic:

    • Direct visualization, highest success rate (90-95%)
    • Requires endoscopist, sedation
    • Cost: AU$500-1,000 per procedure

  2. Fluoroscopic:

    • Radiologist-guided, 80-90% success
    • Radiation exposure

  3. Electromagnetic (Cortrak):

    • Bedside technique using external receiver to track tube tip
    • Success 80-90%, requires training [28]
    • Cost: AU$200-300 per tube

  4. Blind Bedside (with or without prokinetics):

    • Least expensive, success 30-50%
    • Improved to 60-70% if metoclopramide or erythromycin given 30 min prior [29]
    • Confirm position with X-ray before feeding

Feeding via Post-Pyloric Tube:

  • Continuous infusion only (jejunum cannot tolerate bolus)
  • Starting rate: 10-20 mL/h, advance by 10-20 mL/h q4-8h
  • Lower aspiration risk, but no proven mortality benefit [27]

Enteral Nutrition in Special Populations

1. Acute Pancreatitis

Traditional Approach: "Pancreatic rest" with PN or NBM (nil by mouth)

Modern Evidence:

  • EN is superior to PN: Reduced infections, organ failure, mortality, cost [35,36]
  • Early EN (within 48h) vs delayed EN: Faster resolution, shorter length of stay [69]

Route:

  • Nasojejunal (NJ) vs Nasogastric (NG):
    • NJ traditionally preferred (avoids stimulation of pancreatic secretion)
    • RCTs show NG non-inferior to NJ in mild-moderate pancreatitis [37,70]
    • "Current practice: Trial NG feeding first; use NJ if NG not tolerated or severe pancreatitis"

Formula:

  • Polymeric formula preferred (no benefit of elemental formulas) [71]
  • Consider low-fat formula (\u003c30% kcal from fat) if severe fat malabsorption

Contraindications: Ileus, abdominal compartment syndrome, bowel ischemia

2. Acute Respiratory Distress Syndrome (ARDS)

Energy Targets:

  • Permissive underfeeding: Target 60-70% of estimated needs for first 7 days may reduce infections and ventilator days (though evidence mixed) [72]
  • EDEN Trial (2012): Trophic feeding (400 kcal/day) vs full feeding (1,300 kcal/day) for 6 days showed no difference in ventilator-free days, mortality [7]

Omega-3 Fatty Acids:

  • Theoretical benefit: Anti-inflammatory (EPA/DHA reduce pro-inflammatory eicosanoids)
  • OMEGA Trial (2011): Enteral omega-3 supplementation in ARDS stopped early for futility (worse outcomes in treatment group) [42]
  • Current guidelines: Do not routinely use omega-3 enriched formulas in ARDS [22]

Feeding Route:

  • Gastric feeding standard
  • Post-pyloric if gastroparesis or high aspiration risk (30-40% of ARDS patients on prone positioning) [73]

3. Sepsis and Septic Shock

Timing:

  • Initiate EN within 24-48 hours after hemodynamic stabilization
  • Avoid EN if escalating vasopressor requirements (norepinephrine \u003e0.5 mcg/kg/min or equivalent) due to NOMI risk [34]

Energy Targets:

  • Permissive underfeeding (15-20 kcal/kg/day) for first 3-5 days
  • EPaNIC trial: Early aggressive PN supplementation to achieve caloric targets worsened outcomes [21]

Protein Targets:

  • 1.2-1.5 g/kg/day to mitigate muscle loss (though ongoing debate regarding optimal protein dose) [48]

Immunonutrition:

  • Avoid arginine-enriched formulas in sepsis (SIGNET trial showed increased mortality) [41]
  • Glutamine supplementation: Previously investigated but no longer recommended (REDOXS trial showed trend toward harm) [74]

4. Burns

Hypermetabolic Response:

  • Energy expenditure increased by 50-100% in major burns (\u003e20% TBSA)
  • Predicted by Curreri formula: 25 kcal/kg + 40 kcal per % TBSA burned

Energy Targets:

  • 30-35 kcal/kg/day (or use indirect calorimetry if available)
  • Advance to target by day 3 to minimize protein-energy deficit

Protein Targets:

  • High protein needs: 2.0-2.5 g/kg/day (or 20-25% of total energy) [49]
  • Wound healing, immune function, offset massive protein losses (exudate, skin)

Micronutrients:

  • High-dose vitamin C (1-2 g/day): May reduce fluid requirements, edema
  • Zinc, selenium supplementation for wound healing

Route:

  • Gastric feeding first-line
  • Post-pyloric if ileus (common in severe burns due to splanchnic hypoperfusion)

Special Considerations:

  • Burns patients often able to eat; supplement EN with oral intake
  • Avoid overfeeding (increases CO₂ production, prolonged ventilation)

5. Traumatic Brain Injury (TBI)

Energy Targets:

  • 25-30 kcal/kg/day (variable due to sedation, paralysis, seizures)
  • Indirect calorimetry preferred (REE highly variable in TBI) [75]

Protein Targets:

  • 1.5-2.0 g/kg/day (increased needs due to catabolism, nitrogen losses)

Timing:

  • Early EN (within 24-48h) associated with improved neurological outcomes, reduced infections [76]

Special Considerations:

  • Intracranial pressure (ICP): EN does not increase ICP [77]
  • Gastric hypomotility: 60% of TBI patients have delayed gastric emptying; use prokinetics or post-pyloric feeding
  • Target normoglycemia: Avoid hyperglycemia (\u003e10 mmol/L) - worsens secondary brain injury
  • Avoid overfeeding: Exacerbates hyperglycemia

Trophic vs Full Feeding

EDEN Trial (2012) [7]

Design: 1,000 patients with acute lung injury randomized to:

  • Trophic feeding: 10-20 mL/h (400 kcal/day) for 6 days, then advance
  • Full feeding: Target 80% of estimated needs (1,300 kcal/day)

Results:

  • No difference in ventilator-free days (14.9 vs 15.0 days, p=0.89)
  • No difference in 60-day mortality (23.2% vs 22.2%)
  • Trophic group: Lower GI intolerance (vomiting, diarrhea), less insulin use
  • Interpretation: Early aggressive feeding does not improve outcomes in ARDS

EAT-ICU Trial (2024) [9]

Design: 3,957 ICU patients randomized to:

  • Early goal-directed EN: Protocol to achieve 100% of energy target by day 3
  • Standard care: Usual feeding practice (achieved ~70% of target)

Results:

  • No difference in 90-day mortality (HR 0.98, 95% CI 0.90-1.08)
  • More GI complications in early goal-directed group (diarrhea 36% vs 32%, vomiting 19% vs 16%)
  • Interpretation: Aggressive early feeding protocols do not reduce mortality and increase GI complications

Clinical Implication: Accept moderate energy deficits in first week of ICU stay; prioritize protein delivery over total calories [78]

Protein Supplementation

Rationale:

  • Critically ill patients are highly catabolic: Muscle protein breakdown 1.5-2× normal
  • ICU-acquired weakness affects 30-50% of mechanically ventilated patients
  • Negative nitrogen balance persists for weeks post-ICU

Protein Targets (ESPEN 2019): [22]

  • Standard ICU: 1.2-1.5 g/kg/day
  • Burns, trauma, sepsis: 1.5-2.0 g/kg/day
  • Burns \u003e20% TBSA: 2.0-2.5 g/kg/day

Sources:

  • High-protein EN formulas (20-25% protein)
  • Protein modules added to standard EN (e.g., Beneprotein, Protifar)
  • IV amino acids (if EN insufficient, though increases cost and complexity)

Evidence:

  • Observational studies suggest higher protein intake associated with improved strength, reduced ICU-acquired weakness [79]
  • EFFORT Trial (2023): Higher protein (≥2.2 g/kg/day) vs standard (≤1.2 g/kg/day) - no difference in Hospital-Free Days, possible harm in AKI subgroup [80]
  • Ongoing debate: Optimal protein dose, timing, and delivery route

Australian/NZ Considerations:

  • ANZICS Nutrition Guidelines (2020) recommend 1.2-1.5 g/kg/day for most ICU patients [24]
  • Higher targets (1.5-2.0 g/kg/day) for burns, trauma, prolonged ICU stay

Australian and New Zealand Context

ANZICS Nutrition Guidelines (2020) [24]

Key Recommendations:

  1. Initiate EN within 24-48 hours in hemodynamically stable patients
  2. Do not routinely monitor GRV; if measured, do not hold feeds unless \u003e500 mL with clinical intolerance
  3. Target energy: 20-25 kcal/kg IBW for first week, then 25-30 kcal/kg
  4. Target protein: 1.2-1.5 g/kg/day (higher for burns, trauma)
  5. Use polymeric formulas as first-line
  6. Do not use immunonutrition (arginine, glutamine, omega-3) in general ICU population
  7. Post-pyloric feeding if gastroparesis or high aspiration risk
  8. Prokinetics: Metoclopramide or erythromycin for gastroparesis (short-term only)

Product Availability (Australia)

Standard Polymeric Formulas:

  • Osmolite, Isosource Standard, Nutrison Standard
  • PBS-listed for inpatient use

High-Protein Formulas:

  • Nutrison Protein Plus, Isosource Protein
  • Non-PBS (hospital formulary varies)

Elemental Formulas:

  • Peptamen, Vital
  • Authority PBS listing (severe malabsorption)

Disease-Specific:

  • Glucerna (diabetes), Nepro (renal), Oxepa (respiratory)
  • Non-PBS; limited availability in some regional/rural ICUs

Access Challenges:

  • Remote/rural ICUs may have limited formula range
  • Home EN: Community pharmacy supply via authority scripts; dietitian assessment required
  • Aboriginal and Torres Strait Islander communities: Telehealth dietitian support, fly-in services for remote ICU patients

Indigenous Health Considerations

Aboriginal and Torres Strait Islander Peoples:

  • Higher rates of diabetes (3.4× non-Indigenous), CKD (3.0×), sepsis [81]
  • Diabetic gastroparesis more common: Prokinetics, glycemic control essential
  • Cultural considerations:
    • Family involvement in nutrition decisions
    • Traditional foods may be requested for blended tube feeds (if safe and practical)
    • "Aboriginal Health Workers (AHWs) can facilitate communication re: EN importance"

Māori (New Zealand):

  • Higher rates of diabetes (2.5× NZ European), CKD, sepsis
  • Whānau-centered care: Involve extended family in EN decisions, especially for long-term PEG/PEJ
  • Tikanga: Respect for cultural practices, karakia (prayer) before procedures

Summary: Key Practice Points

  1. Initiate EN within 24-48 hours in hemodynamically stable ICU patients with functioning GI tract
  2. Early EN benefits: Maintains gut barrier, reduces infections, lower cost than PN
  3. Avoid aggressive early feeding: Permissive underfeeding (60-70% targets) for first 3-5 days acceptable
  4. Do not routinely monitor GRV; focus on clinical assessment of tolerance
  5. Gastric feeding first-line; post-pyloric if gastroparesis or high aspiration risk
  6. Polymeric formulas for most patients; avoid immunonutrition in general ICU population
  7. Energy targets: 20-25 kcal/kg/day initially, advance to 25-30 kcal/kg/day by day 5-7
  8. Protein targets: 1.2-1.5 g/kg/day (higher in burns, trauma: 1.5-2.5 g/kg/day)
  9. Prevent refeeding syndrome: Identify high-risk patients, correct deficits, start low and go slow
  10. Manage complications proactively: Aspiration (elevate HOB, post-pyloric feeding), diarrhea (review medications, rule out C. diff), gastroparesis (prokinetics, post-pyloric feeding)

Assessment Content

SAQ Practice Questions

SAQ 1: Early Enteral Nutrition and Evidence-Based Practice

Scenario: A 65-year-old man is admitted to ICU with severe community-acquired pneumonia requiring mechanical ventilation. He has been intubated for 18 hours and is hemodynamically stable on norepinephrine 0.1 mcg/kg/min. The nursing staff ask whether to commence enteral nutrition.

Question (15 marks total):

(a) Outline the rationale for early enteral nutrition in critically ill patients. (5 marks)

(b) Describe the key findings of the NUTRIREA-2 trial and their implications for gastric residual volume monitoring. (5 marks)

(c) What energy and protein targets would you recommend for this patient in the first week of ICU admission, and what is the evidence basis for these targets? (5 marks)

Model Answer:

(a) Rationale for Early Enteral Nutrition (5 marks)

Early EN (within 24-48 hours of ICU admission) is recommended because:

Gut Mucosal Barrier Integrity (2 marks):

  • Intestinal epithelial cells derive 60-70% of energy from luminal nutrients (glutamine, SCFA)
  • Absence of enteral feeding \u003e48h → villous atrophy, increased permeability, bacterial translocation
  • EN maintains tight junctions and enterocyte viability

Immune Function (1 mark):

  • GALT (70% of immune system) requires enteral stimulation
  • Maintains secretory IgA production and commensal microbiota

Clinical Outcomes (2 marks):

  • Meta-analysis: EN vs PN reduces infections (RR 0.64), shorter ICU stay
  • Lower glycemic variability and insulin requirements
  • Cost: EN 10-20% of PN cost

(b) NUTRIREA-2 Trial Findings and Implications (5 marks)

Study Design (1 mark):

  • 452 mechanically ventilated ICU patients randomized to GRV monitoring (feeds held if \u003e250 mL) vs no GRV monitoring

Key Findings (2 marks):

  • No difference in VAP rates (16.7% vs 16.3%)
  • No difference in aspiration events, ICU mortality, or length of stay
  • No GRV group received significantly more nutrition (1,534 vs 1,284 kcal/day, p\u003c0.001)

Implications for Practice (2 marks):

  • Routine GRV monitoring not necessary and reduces EN delivery without improving safety
  • Current guidelines: Do not routinely measure GRV; if measured, hold feeds only if \u003e500 mL with clinical signs (vomiting, distension, pain)
  • Focus on clinical assessment (abdominal exam, aspiration events) rather than arbitrary GRV thresholds

(c) Energy and Protein Targets (5 marks)

Energy Targets (2 marks):

  • First 3-5 days: 20-25 kcal/kg ideal body weight (IBW)/day - permissive underfeeding
  • After day 5: Advance to 25-30 kcal/kg IBW/day if tolerating

Evidence Basis (1 mark):

  • EDEN Trial: Trophic (400 kcal/day) vs full feeding (1,300 kcal/day) in ARDS - no difference in outcomes
  • EAT-ICU Trial: Early goal-directed EN vs standard care - no mortality benefit, increased GI complications
  • EPaNIC Trial: Early aggressive PN to achieve targets worsened outcomes

Protein Targets (2 marks):

  • 1.2-1.5 g/kg IBW/day (ESPEN 2019, ANZICS 2020 guidelines)
  • Higher priority than total calories to mitigate muscle loss and ICU-acquired weakness
  • For severe sepsis/burns/trauma: Consider 1.5-2.0 g/kg/day

SAQ 2: Enteral Nutrition Complications and Management

Scenario: A 72-year-old woman is admitted to ICU following emergency laparotomy for perforated diverticulitis. She has been receiving continuous NG feeding at 80 mL/h (standard polymeric formula) for 5 days. On day 6, she develops 6 episodes of loose stool (total ~800 mL) and the nursing staff request review. She remains intubated and sedated, hemodynamically stable, and on day 3 of IV piperacillin-tazobactam.

Question (15 marks total):

(a) List six causes of diarrhea in ICU patients receiving enteral nutrition. (3 marks)

(b) Describe your systematic approach to investigating and managing this patient's diarrhea. (7 marks)

(c) Under what circumstances would you consider stopping enteral nutrition for diarrhea, and what are the risks of doing so? (5 marks)

Model Answer:

(a) Six Causes of Diarrhea in ICU Patients (3 marks - 0.5 marks each)

  1. Medication-related: Antibiotics (most common), sorbitol-containing elixirs, magnesium, prokinetics
  2. Clostridioides difficile infection (CDI): 10-20% of ICU diarrhea
  3. Formula-related: High osmolality (elemental formulas), bolus feeding, fat malabsorption
  4. Fecal impaction with overflow: Opioids, immobility
  5. Bowel pathology: Ischemic colitis (vasopressors), IBD flare
  6. Infectious gastroenteritis: Viral (Norovirus), bacterial

(b) Systematic Approach to Investigation and Management (7 marks)

1. Clinical Assessment (1 mark):

  • Digital rectal exam (exclude fecal impaction)
  • Abdominal exam (distension, tenderness, bowel sounds)
  • Review stool chart (frequency, volume, Bristol type)

2. Review Medications (1 mark):

  • Antibiotics: Piperacillin-tazobactam disrupts gut microbiome
  • Sorbitol-containing suspensions (common in ICU liquid medications)
  • Magnesium-containing drugs (antacids, laxatives)
  • Consider de-escalation or cessation of non-essential drugs

3. Microbiological Testing (2 marks):

  • C. difficile stool PCR/toxin assay: High-risk patient (antibiotics, older age, ICU stay)
  • If positive: Isolate patient, contact precautions, oral vancomycin 125 mg q6h or fidaxomicin 200 mg BD
  • Stool culture if bloody diarrhea or fever

4. Modify Enteral Feeding Regimen (2 marks):

  • Reduce infusion rate by 50% (to 40 mL/h) and gradually re-escalate over 24-48h
  • Continue EN if possible (unless severe diarrhea \u003e2 L/day)
  • Consider adding soluble fiber (guar gum, pectin) to bulk stool
  • Switch to peptide-based formula only if malabsorption suspected (unlikely in this case)

5. Pharmacological Management (1 mark):

  • Loperamide 2-4 mg PO q6h PRN (only if C. diff negative)
  • Probiotics: Insufficient evidence; potential harm in immunocompromised

(c) When to Stop EN and Risks (5 marks)

Indications to Stop EN (2 marks):

  • Severe diarrhea (\u003e2 L/day) causing:
    • Severe metabolic acidosis (hyperchloremic from bicarbonate loss)
    • Electrolyte derangements requiring frequent repletion (hypokalemia, hypomagnesemia)
    • Perianal skin breakdown (sacral pressure ulcer risk)
  • Clinical concern for bowel ischemia: Bloody diarrhea, lactic acidosis, abdominal pain
  • Suspected bowel obstruction or perforation

Risks of Stopping EN (3 marks):

  • Gut mucosal atrophy: Villous atrophy begins within 24-48 hours; increased bacterial translocation
  • Nutritional deficit: Protein-energy malnutrition worsens (already 5 days post-op with high catabolic needs)
  • Need for parenteral nutrition: If EN stopped \u003e3-5 days → consider PN (higher cost, infection risk, no gut stimulation)
  • Delayed recovery: Slower return to oral intake

Preferred Approach: Reduce EN rate rather than stop completely; maintain some trophic feeding (10-20 mL/h) to preserve gut function while managing diarrhea

Viva Scenarios

Viva 1: Enteral Nutrition Initiation and Route Selection

Scenario: You are the ICU consultant. A 58-year-old man with COPD has been intubated for 36 hours with community-acquired pneumonia. He is on norepinephrine 0.15 mcg/kg/min. The bedside nurse asks if enteral feeding should be commenced.

Examiner: "Would you start enteral feeding in this patient?"

Expected Response: "Yes, provided he is hemodynamically stable. He has been intubated for 36 hours, which is within the 24-48 hour window for early EN. His norepinephrine dose is 0.15 mcg/kg/min, which is relatively low and stable, suggesting adequate tissue perfusion. Early EN within 24-48 hours maintains gut mucosal integrity, reduces infectious complications, and is associated with better outcomes compared to delayed feeding or PN. I would confirm there are no absolute contraindications such as bowel ischemia, obstruction, or uncontrolled shock before starting."

Examiner: "What are the absolute contraindications to enteral feeding?"

Expected Response: "Absolute contraindications include:

  1. Bowel ischemia or infarction - feeding increases metabolic demand and worsens ischemia
  2. Mechanical bowel obstruction - tumor, adhesions, volvulus
  3. High-output proximal small bowel fistula (\u003e500 mL/day) - EN increases fistula output
  4. Severe GI hemorrhage requiring active resuscitation
  5. Hemodynamic instability with escalating vasopressor requirements suggests inadequate splanchnic perfusion and risk of non-occlusive mesenteric ischemia, or NOMI"

Examiner: "At what vasopressor dose would you be concerned about starting EN?"

Expected Response: "There is no absolute cutoff, but I would be cautious with norepinephrine \u003e0.5 mcg/kg/min or if vasopressor doses are escalating. This suggests inadequate splanchnic perfusion and increased risk of NOMI, which occurs in 0.3-3% of ICU patients on vasopressors. In unstable patients, I would delay EN until hemodynamic stabilization, then consider starting with trophic feeding at 10-20 mL/h and monitor closely for signs of intolerance such as lactic acidosis, abdominal distension, or bloody aspirates."

Examiner: "Which route would you use - nasogastric or post-pyloric?"

Expected Response: "I would start with nasogastric feeding as first-line. NG is easier to insert, does not require endoscopy or fluoroscopy, and allows gastric acid sterilization of feed. Post-pyloric feeding is reserved for patients with documented gastroparesis, recurrent aspiration, or high aspiration risk. In this patient, unless he has specific risk factors, NG feeding is appropriate."

Examiner: "He has a GCS of 5 on sedation. Does this change your aspiration risk assessment?"

Expected Response: "Yes, a low GCS is a risk factor for aspiration, along with impaired gag reflex and supine positioning. To mitigate aspiration risk, I would:

  1. Elevate head of bed to 30-45° - reduces aspiration by 50-70%
  2. Use continuous infusion rather than bolus feeding
  3. Avoid routine GRV monitoring per NUTRIREA-2 trial and current ANZICS guidelines, which showed GRV monitoring does not reduce aspiration risk but does reduce EN delivery
  4. If he develops signs of intolerance - vomiting, high GRV \u003e500 mL, recurrent aspiration - I would trial prokinetics (metoclopramide or erythromycin) and consider post-pyloric feeding"

Examiner: "The nurse measures a gastric residual volume of 300 mL on day 2 of feeding. What do you do?"

Expected Response: "I would continue feeding. The NUTRIREA-2 trial showed that routine GRV monitoring does not reduce VAP or aspiration rates but does result in less nutrition being delivered. Current guidelines recommend not stopping feeds unless GRV \u003e500 mL and there are clinical signs of intolerance such as vomiting, abdominal distension, or pain. A GRV of 300 mL alone is not an indication to stop EN. I would perform a clinical assessment - abdominal exam, check for vomiting, review trends - and continue feeding if no concerning signs."

Examiner: "On day 3, he vomits 200 mL of feed. What now?"

Expected Response: "Vomiting is a sign of feed intolerance and increases aspiration risk. I would:

  1. Temporarily hold EN and place tube on free drainage
  2. Clinical assessment: Abdominal exam (distension, pain, bowel sounds), review medications (opioids, sedation)
  3. Consider prokinetics: Metoclopramide 10 mg IV q6h or erythromycin 250 mg IV q6h to improve gastric emptying
  4. Restart EN at reduced rate (e.g., 20-30 mL/h) once vomiting settles, and slowly advance
  5. If recurrent vomiting despite prokinetics, consider post-pyloric feeding to bypass the stomach"

Examiner: "How would you place a post-pyloric tube?"

Expected Response: "Several techniques are available:

  1. Endoscopic placement: Highest success rate (90-95%), requires endoscopist and sedation
  2. Fluoroscopic placement: Radiologist-guided, 80-90% success, radiation exposure
  3. Electromagnetic-guided (Cortrak): Bedside technique using external receiver to track tube tip, success 80-90%, cost-effective for ICUs with trained staff
  4. Blind bedside placement: Least expensive but lower success (30-50%); improved to 60-70% if metoclopramide or erythromycin given 30 minutes prior to facilitate passage through pylorus

In this ICU, I would use [state local practice - e.g., endoscopic if available, or Cortrak if nursing staff trained]. Position must be confirmed with X-ray before initiating feeding."

Examiner: "What formula would you use?"

Expected Response: "I would use a standard polymeric formula (e.g., Osmolite, Nutrison Standard). Polymeric formulas are first-line for patients with normal GI function - they contain intact proteins, long-chain triglycerides, and complex carbohydrates, are well-tolerated, and cost-effective.

I would not use:

  • Elemental formulas: Reserved for malabsorption (short bowel, pancreatic insufficiency); 3-5× more expensive with no proven benefit in general ICU population
  • Immune-modulating formulas (arginine, glutamine, omega-3): No benefit in general ICU; arginine may be harmful in sepsis (SIGNET trial), omega-3 harmful in ARDS (OMEGA trial)

If this patient had specific needs - e.g., poorly controlled diabetes - I might consider a diabetic formula (Glucerna), but a standard formula with good glycemic control is usually sufficient."

Examiner: "What are your energy and protein targets?"

Expected Response: "For the first 3-5 days, I would target permissive underfeeding:

  • Energy: 20-25 kcal/kg ideal body weight per day
  • Protein: 1.2-1.5 g/kg IBW per day

This is based on the EDEN and EAT-ICU trials, which showed that early aggressive feeding does not improve outcomes and may increase GI complications. After day 5, I would advance energy to 25-30 kcal/kg/day while prioritizing protein delivery, as protein is more important than total calories for mitigating ICU-acquired weakness and muscle loss. If indirect calorimetry were available, I would use measured resting energy expenditure to guide targets, as predictive equations often overestimate in critically ill patients."

Examiner: "Thank you. Any questions?"

Viva 2: Refeeding Syndrome and Complex Nutrition Management

Scenario: A 45-year-old woman with alcohol use disorder is admitted to ICU with aspiration pneumonia. She weighs 45 kg (BMI 16.5 kg/m²) and reports minimal oral intake for the past 3 weeks. She is intubated, sedated, and hemodynamically stable. You are asked about commencing enteral nutrition.

Examiner: "What concerns do you have about starting enteral nutrition in this patient?"

Expected Response: "This patient is at very high risk of refeeding syndrome. She has three major risk factors:

  1. BMI \u003c16 kg/m² (16.5)
  2. Minimal nutritional intake for \u003e10 days (3 weeks)
  3. Likely alcohol-related nutritional deficiencies (thiamine, magnesium, phosphate)

Refeeding syndrome occurs when nutrition is reintroduced after prolonged starvation. The insulin surge from feeding drives glucose, phosphate, potassium, and magnesium intracellularly, causing severe hypophosphatemia, hypokalemia, and hypomagnesemia. Hypophosphatemia is the hallmark and can cause respiratory failure (diaphragm weakness), cardiac failure, hemolysis, rhabdomyolysis, and seizures. This patient requires careful pre-feeding assessment, electrolyte correction, and cautious advancement of nutrition."

Examiner: "How would you prevent refeeding syndrome?"

Expected Response: "Prevention involves four key steps:

1. Pre-Feeding Electrolyte Assessment and Correction (2-3 days before full feeding):

  • Measure baseline phosphate, potassium, magnesium, glucose
  • Thiamine replacement is critical: 200-300 mg IV daily for 3 days before feeding (prevents Wernicke's encephalopathy in alcohol use disorder)
  • Correct electrolyte deficits:
    • "Phosphate: If \u003c0.65 mmol/L, replace IV"
    • "Potassium: Target \u003e3.5 mmol/L"
    • "Magnesium: Target \u003e0.7 mmol/L"

2. Start Low, Go Slow:

  • Begin feeding at 10-20 kcal/kg/day (50% of estimated target) = ~500-900 kcal/day for this patient
  • Advance by 25% every 2-3 days only if electrolytes remain stable

3. Intensive Electrolyte Monitoring:

  • Measure phosphate, potassium, magnesium daily (or more frequently if abnormal) for first 5-7 days
  • If phosphate drops \u003c0.65 mmol/L: Stop advancing feeds, replace IV, do not increase nutrition until corrected

4. Multivitamin and Trace Element Supplementation:

  • Daily multivitamin (including thiamine 100 mg ongoing)
  • Zinc, selenium if deficient"

Examiner: "On day 2 of feeding at 20 mL/h, her phosphate is 0.55 mmol/L (normal 0.8-1.5). What do you do?"

Expected Response: "This is moderate refeeding hypophosphatemia requiring immediate action:

1. Stop Advancing Feeds: Hold current rate at 20 mL/h (do not increase); do not stop feeding completely unless severe symptoms 2. IV Phosphate Replacement:

  • For phosphate 0.4-0.65 mmol/L: IV sodium phosphate 0.3-0.6 mmol/kg over 12-24 hours
  • For this 45 kg patient: ~15-25 mmol over 12-24h
  • Monitor serum phosphate every 6-12 hours during replacement 3. Check and Correct Other Electrolytes: Potassium, magnesium (often co-depleted) 4. Clinical Monitoring: Respiratory function (diaphragm weakness), cardiac telemetry (arrhythmias), neuromuscular exam 5. Resume Feed Advancement: Only after phosphate \u003e0.65 mmol/L and stable for 24-48h; advance very slowly (10-20% every 2-3 days)"

Examiner: "She also has a history of chronic pancreatitis. Does this change your feeding plan?"

Expected Response: "Yes, in several ways:

Route Selection:

  • Enteral nutrition is preferred over PN even in pancreatitis (reduces infections, organ failure, mortality)
  • Post-pyloric (nasojejunal) feeding is traditionally preferred as it bypasses the stomach and does not stimulate pancreatic secretion via gastrin release
  • However, recent RCTs suggest nasogastric feeding may be non-inferior in mild-moderate pancreatitis
  • I would trial NG feeding first, and switch to NJ if not tolerated (abdominal pain, nausea, vomiting)

Formula Selection:

  • Standard polymeric formula is first-line (no benefit of elemental formulas in pancreatitis)
  • Consider low-fat formula (\u003c30% calories from fat) if she develops steatorrhea or severe fat malabsorption, though evidence for benefit is limited

Contraindications to EN in Pancreatitis:

  • Ileus, abdominal compartment syndrome, bowel ischemia
  • If present, delay EN until resolved

Pancreatic Enzyme Replacement (if chronic pancreatitis with exocrine insufficiency):

  • May require pancrelipase (Creon) supplementation via feeding tube to improve fat absorption"

Examiner: "On day 5, she develops 8 episodes of watery diarrhea. Your approach?"

Expected Response: "Diarrhea is very common in ICU patients on EN (20-68% incidence). My systematic approach:

1. Clinical Assessment:

  • Digital rectal exam (exclude fecal impaction with overflow - common with opioids)
  • Abdominal exam (distension, tenderness, bowel sounds)
  • Review stool chart (volume, frequency, Bristol type)

2. Review Medications (Most Common Cause):

  • Antibiotics: Disrupts gut microbiome
  • Sorbitol-containing liquid medications: Very common in ICU
  • Magnesium: Antacids, supplements
  • Prokinetics: If she's on metoclopramide or erythromycin
  • Consider stopping non-essential medications

3. Microbiological Testing:

  • C. difficile stool PCR/toxin: High-risk patient (likely antibiotics for aspiration pneumonia, ICU stay, alcohol-associated immune dysfunction)
  • If positive: Isolate, contact precautions, oral vancomycin 125 mg q6h or fidaxomicin 200 mg BD

4. Modify EN Regimen:

  • Reduce rate by 50% and gradually re-escalate over 24-48h
  • Continue EN if possible (unless \u003e2 L/day or metabolic complications)
  • Consider adding soluble fiber (guar gum) to bulk stool
  • Switch to peptide-based formula only if malabsorption suspected (chronic pancreatitis with exocrine insufficiency)

5. Pharmacological:

  • Loperamide 2-4 mg PO q6h if C. diff negative
  • Pancreatic enzyme replacement (Creon) if chronic pancreatitis with steatorrhea

Do NOT stop EN unless severe diarrhea causing metabolic acidosis, electrolyte derangements, or perianal breakdown. Stopping EN risks gut atrophy, bacterial translocation, and further delays nutritional recovery in this already malnourished patient."

Examiner: "She improves and is extubated on day 7. She is managing small amounts orally but unable to meet nutritional needs. What is your plan?"

Expected Response: "I would continue EN as supplemental feeding alongside oral intake:

1. Reassess Nutritional Needs:

  • Dietitian review to quantify oral intake (typically 30-50% of needs initially post-extubation)
  • Calculate deficit between oral intake and target (25-30 kcal/kg, 1.2-1.5 g protein/kg now she's recovering)

2. Continue NG Feeding:

  • Transition to nocturnal EN (overnight continuous infusion, e.g., 10pm-6am) to avoid interfering with daytime oral intake
  • Allows her to participate in meals, therapy, mobilization during the day
  • Gradually wean EN as oral intake improves (assessed daily by dietitian)

3. Optimize Oral Intake:

  • High-protein oral supplements (e.g., Ensure Plus, Fortisip) between meals
  • Encourage small frequent meals (6 meals/day rather than 3 large)
  • Modify diet texture if dysphagia (speech pathology swallow assessment)

4. Long-Term Access:

  • If unable to meet nutritional needs orally by 4-6 weeks, consider PEG (percutaneous endoscopic gastrostomy) for long-term home EN
  • Requires MDT discussion (patient, family, dietitian, gastroenterologist)

5. Address Alcohol Use Disorder:

  • Addiction medicine consult for ongoing management, relapse prevention
  • Thiamine 100 mg PO daily long-term to prevent Wernicke-Korsakoff syndrome
  • Nutritional rehabilitation is part of addiction recovery"

Examiner: "Excellent. Thank you."

References

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Further Reading

ANZICS Guidelines:

  • Australian and New Zealand Intensive Care Society Clinical Trials Group Position Statement on Intensive Care Nutrition (2020)

International Guidelines:

  • ESPEN Guideline on Clinical Nutrition in the ICU (Singer et al., 2019) - PMID: 30348463
  • ASPEN/SCCM Guidelines for Nutrition Support in Critically Ill Adults (McClave et al., 2016) - PMID: 26773077

Landmark Trials:

  • EPaNIC Trial (Casaer et al., 2011) - PMID: 21714640
  • EDEN Trial (Rice et al., 2012) - PMID: 22307571
  • NUTRIREA-2 Trial (Reignier et al., 2013) - PMID: 23321763
  • EAT-ICU Trial (Allingstrup et al., 2017) - PMID: 28936788

Review Articles:

  • Chapman MJ, Peake SL, Bellomo R, et al. Energy-dense versus routine enteral nutrition in the critically ill. N Engl J Med. 2018;379(19):1823-34. PMID: 30280928
  • Heyland DK, Dhaliwal R, Jiang X, Day AG. Identifying critically ill patients who benefit the most from nutrition therapy: the development and initial validation of a novel risk assessment tool. Crit Care. 2011;15(6):R268. PMID: 22082149

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