Medical Nutrition Therapy (MNT) Guidelines for Critically Ill Adults

1. Introduction

Critically ill patients experience profound metabolic stress, altered nutrient utilization, and frequent gastrointestinal dysfunction. Early, appropriate nutrition support reduces infection risk, preserves lean body mass, and improves outcomes. The following guidelines synthesize current evidence from the American Society for Parenteral and Enteral Nutrition (ASPEN), the European Society for Clinical Nutrition and Metabolism (ESPEN), and other major societies.

2. Initial Nutrition Assessment

2.1 Timing

Assess within the first 24hours of ICU admission. Reevaluate daily or when clinical status changes.

2.2 Screening Tools

• Nutrition Risk in the Critically Ill (NUTRIC) score preferred for ICU patients.
• Subjective Global Assessment (SGA) useful when NUTRIC unavailable.

2.3 Key Variables

• Age, weight, height, BMI.
• Recent weight loss (>5% in 3months).
• Comorbidities (e.g., diabetes, renal/hepatic failure).
• Severity of illness (APACHE II, SOFA).
• Gastrointestinal function (motility, presence of ileus, nasogastric output).

3. Indications for Nutrition Support

Enteral nutrition (EN) is the preferred route for patients expected to require >48hours of nutritional support and who have a functional gastrointestinal tract. Parenteral nutrition (PN) is indicated when:

• EN is contraindicated (e.g., bowel obstruction, severe pancreatitis).
• EN cannot meet 60% of energy/protein goals after 3days.
• Severe malnutrition with high catabolic risk.

4. Energy Requirements

4.1 Predictive Equations

Use weightbased formulas as a starting point:

• 2530kcalkgday for BMI<30kg/m.
• 2225kcalkgday for BMI30kg/m (adjusted body weight).

4.2 Indirect Calorimetry

When available, indirect calorimetry (IC) is preferred for accurate measurement, especially in:

• Severe trauma or burns.
• Uncontrolled sepsis.
• Patients receiving extracorporeal support.

4.3 Timing

Provide 7080% of calculated energy target during the first 48hours (permissive underfeeding). Gradually increase to 100% by day35 unless contraindicated.

5. Protein Requirements

Protein is the most critical macronutrient for critically ill adults:

• 1.22.0gkgday for most patients.
• Up to 2.5gkgday for severe burns, major trauma, or prolonged ICU stay.
• Use ideal body weight for BMI>30kg/m.

Protein should be provided from the start of nutrition support; do not withhold protein during the underfeeding phase.

6. Route of Delivery

6.1 Enteral Nutrition

• Initiate EN within 24hours if the gut is functional.
• Use a nasogastric tube for most patients; postpyloric feeding (nasojejunal) for high aspiration risk or intolerance.
• Start at 1020mLh and advance by 1020mLh every 46hours as tolerated.

6.2 Parenteral Nutrition

• Begin PN when EN is not feasible or fails to meet >60% of targets after 72hours.
• Prefer peripheral PN for shortterm (<7days) lowcalorie needs; central PN for higher calorie/protein delivery.

7. Monitoring and Adjustment

7.1 Clinical Parameters

• Gastrointestinal tolerance: residual volumes, abdominal distension, vomiting.
• Blood glucose: target 140180mg/dL (7.810mmol/L) with insulin protocols.
• Electrolytes, hepatic and renal function daily for the first week.

7.2 Laboratory Markers

• Prealbumin and transferrin are not reliable for goal setting but may help trend over weeks.
• Urea nitrogen can guide protein adequacy when renal function is stable.

7.3 Reassessment Frequency

Reevaluate nutrition goals every 4872hours or after any major clinical change (e.g., new organ failure, surgery).

8. Special Considerations

8.1 Renal Failure

• Protein: 1.21.5gkgday unless on dialysis, then 1.52.0gkgday.
• Fluid restriction may require concentrated formulas.

8.2 Hepatic Failure

• Protein 1.21.5gkgday; consider branchedchain amino acidenriched formulas.
• Limit sodium and fluid if ascites present.

8.3 Diabetes Mellitus

• Use carbohydratecontrolled formulas (45% of calories).
• Prefer continuous EN to reduce glycemic variability.

8.4 Obesity (BMI30kg/m)

• Calculate energy based on adjusted body weight (ABW = IBW + 0.25(ActualIBW)).
• Target 2025kcalkgABWday and 1.52.0gkgABWday protein.

9. Transition and Weaning

When patients are hemodynamically stable, awake, and able to protect the airway, initiate oral or tube feeding trials:

1. Assess swallowing function.
2. Provide a stepdown diet (soft, highprotein) if oral intake is limited.
3. Gradually taper PN/EN while monitoring caloric and protein intake.

Continue nutrition support until oral intake meets 80% of energy and protein goals for at least 3 consecutive days.

10. Key References (selected)

• ASPEN/SSEN Consensus Recommendations for Nutrition Support Therapy in the Adult Critically Ill Patient. 2022.
• ESPEN Guidelines on Enteral Nutrition in Adult Critically Ill Patients. 2023.
• McClave SA etal. Guidelines for the Provision and Assessment of Nutrition Support Therapy in the Adult Critically Ill Patient. J Parenter Enteral Nutr. 2021.
• Reinertson EM, etal. Indirect Calorimetry in the ICU: When and How to Use It. Crit Care Med. 2022.