What is Enteral Nutrition (EN) and how is it used in patients with a functioning gastrointestinal tract who are unable to consume food orally?

What is Enteral Nutrition (EN)?

Enteral nutrition (EN) is the delivery of nutrients via feeding tubes beyond the esophagus to patients with a functioning gastrointestinal tract who cannot meet their nutritional requirements through normal oral intake. 1, 2

Definition and Core Concept

• EN encompasses tube feeding delivered through various access routes (nasogastric, nasojejunal, gastrostomy, jejunostomy) to provide complete nutrition when oral intake is inadequate 1, 3
• The fundamental requirement is a functional gastrointestinal tract that can absorb nutrients 1, 4
• EN is distinct from oral nutritional supplements (ONS), which are consumed by mouth, though both fall under the broader category of enteral feeding 1

Primary Indications

EN should be initiated when patients cannot meet 60% of their nutritional requirements orally for more than 7-10 days, or when complete inability to eat is anticipated for more than one week. 1

Specific clinical scenarios include:

• Neurological conditions impairing swallow function (stroke, amytrophic lateral sclerosis, Parkinson's disease) 3
• Mechanical ventilation and altered mental status preventing oral intake 3
• Malnutrition or nutritional risk with inadequate oral intake (<10 kcal/kg/day or deficit of 600-800 kcal/day) 1
• Head and neck cancer, gastrointestinal malignancies, and Crohn's disease 1

Why EN is Preferred Over Parenteral Nutrition

EN reduces infectious complications by approximately 30-36% compared to parenteral nutrition and should always be the first-line route when the gut is functional. 4, 5

Key advantages:

• Maintains gut barrier function and mucosal integrity, reducing bacterial translocation 4, 5
• Significantly more cost-effective than parenteral nutrition while providing equal or superior outcomes 4
• Reduces hospital length of stay by nearly one day when initiated early 4
• Lower rates of septic complications, organ failure, and need for surgical interventions 4, 5

Timing of Initiation

In critically ill patients, EN should be started within 24-48 hours of admission if hemodynamically stable, even before full nutritional assessment is complete. 1, 5

• All ICU patients not expected to resume full oral diet within 3 days require EN 1, 5
• Surgical patients unable to eat for more than 3 days postoperatively should receive EN 1
• Delay of 7-14 days for preoperative EN is justified only in severely malnourished patients (weight loss >10-15%, BMI <18.5, albumin <30 g/L) 1

Formula Selection

Standard polymeric whole-protein formulas are appropriate for most patients, as specialized formulas show no consistent clinical advantage in general populations. 1, 5

• Commercial formulas are strongly preferred over kitchen-prepared feeds due to superior safety, consistent nutritional content, and reduced infection risk 5
• Disease-specific formulas lack robust evidence for most conditions 2
• Immune-modulating formulas (arginine, nucleotides, omega-3 fatty acids) may benefit trauma patients and mild sepsis (APACHE II <15) but are contraindicated in severe sepsis 1

Delivery Methods

Gastric feeding via nasogastric tube is the preferred initial route, as it is more physiological than post-pyloric feeding. 2

Route selection algorithm:

• Nasogastric tube: First-line for short-term feeding (<4-6 weeks) 2
• Post-pyloric (nasojejunal): Reserved for high aspiration risk or gastric intolerance 1, 2
• Gastrostomy/jejunostomy: When EN duration exceeds 4-6 weeks 1, 2
• Intermittent bolus feeding: More physiological when tolerated 2
• Continuous infusion: For severely diseased gut or intolerance to bolus feeds 2

Energy and Protein Targets

During acute critical illness, limit energy provision to 20-25 kcal/kg/day to avoid overfeeding; increase to 25-30 kcal/kg/day during recovery phase. 1, 5

• Protein requirements: 1.2-2.0 g/kg/day depending on clinical condition 5
• Start at low flow rates (10-20 ml/hour) and advance gradually over 5-7 days 5
• Energy provision exceeding 25 kcal/kg/day during acute phase worsens outcomes 1, 5

Critical Pitfalls to Avoid

Never default to parenteral nutrition simply because enteral feeding seems "difficult"—the evidence overwhelmingly supports attempting EN first even in challenging cases. 4

• Overfeeding during acute illness (>25 kcal/kg/day) increases complications and mortality 1, 5
• Delaying EN initiation beyond 24-48 hours in ICU patients loses the window for optimal benefit 4, 5
• Stopping feeds for high gastric residuals without clinical signs of intolerance is unnecessary 5
• Failing to monitor for refeeding syndrome in malnourished patients can cause life-threatening electrolyte disturbances 5, 6

When Parenteral Nutrition is Indicated

Parenteral nutrition should only be used when EN is contraindicated (intestinal obstruction, mesenteric ischemia, abdominal compartment syndrome) or fails to meet >60% of requirements after 3-7 days in severely malnourished patients. 1, 5

• Unrepaired anastomotic leaks or high-output fistulas without distal feeding access 1
• Severe malabsorption or intractable vomiting despite optimal medical management 1
• Supplemental parenteral nutrition may be added if EN alone cannot meet requirements after adequate trial 1