Metabolism and Nutrition Therapy in Burn Patients

Introduction

Burn injuries trigger profound metabolic changes that dramatically increase nutritional requirements. Major burns cause hypermetabolism that can persist for months after injury, making proper nutritional support critical for optimal healing. Nutrition therapy aims to support wound healing, maintain lean body mass, modulate hypermetabolic response, and reduce complications.

This guide explores the metabolic changes following burn injuries and evidence-based nutritional interventions for healthcare providers managing burn patients.

Metabolic Response to Burn Injury

Severe burn injuries induce significant physiological changes:

• Hypermetabolism: Resting energy expenditure can increase by 100-200% above normal, primarily due to increased heat production, gluconeogenesis, and protein breakdown.
• Hypercatabolism: Marked increase in protein catabolism resulting in rapid loss of lean body mass without nutritional intervention.
• Insulin resistance: Impaired glucose utilization despite increased insulin secretion, often requiring close monitoring.
• Inflammatory response: Release of cytokines and stress hormones including cortisol, catecholamines, and glucagon.
• Elevated core temperature: Due to altered hypothalamic set-point and increased heat production.

The hypermetabolic response peaks approximately 7-14 days post-injury and can persist for up to 12-24 months, depending on burn severity and patient management.

Nutritional Assessment in Burn Patients

Comprehensive nutritional assessment forms the foundation of effective therapy:

Initial Assessment

• Burn size (% TBSA) and depth classification
• Pre-injury nutritional status and body weight
• Height and current weight measurements
• Comorbidities affecting nutrition (e.g., diabetes, malnutrition)
• Gastrointestinal function and history
• Past medical and surgical history

Ongoing Monitoring

• Regular weighing with consistency (same time of day, equipment, clothing)
• Monitoring nitrogen balance studies
• Assessment of prealbumin, transferrin, and other biochemical markers
• Measurement of resting energy expenditure when possible
• Tracking wound healing progress
• Documentation of tolerance to nutritional support

Regular reassessment is essential as nutritional needs change throughout different phases of burn recovery.

Energy Requirements in Burn Patients

Accurately determining energy needs is critical to avoid both underfeeding (exacerbating catabolism) and overfeeding (increasing complications). Several equations can estimate needs:

• Curreri formula: 25 kcal/kg + 40 kcal/% TBSA burn
• Harris-Benedict equation: Multiplied by activity (1.2-1.3) and injury (1.5-2.0) factors
• Schofield equation: With appropriate injury factors
• Indirect calorimetry: The gold standard when available

Energy requirements typically range from 25-35 kcal/kg/day in pediatric patients and 30-40 kcal/kg/day in adults, though individual variation is substantial. In the early acute phase, requirements may be lower, with gradual increases as hypermetabolism peaks around 7-14 days post-injury.

Protein Requirements

Protein needs increase dramatically after burn injury to support tissue repair, immune function, and minimize lean body mass loss:

• Adults: 2.0-3.0 g/kg/day
• Pediatrics: 3.0-4.0 g/kg/day
• Additional 10-20% for patients with significant infections or extensive wound care

High-biological-value proteins such as whey, casein, soy, and complete protein blends should constitute the majority of protein intake. Amino acid supplementation, particularly glutamine and arginine, may offer additional benefits in wound healing and immune function.

Nitrogen balance studies can guide protein adequacy (goal of +2 to +4 g/day). Markers such as prealbumin can also help monitor nutritional status, though interpretation must consider the inflammatory state.

Carbohydrate Requirements

Carbohydrates provide the primary energy source during the hypermetabolic phase and help spare protein from being used for energy:

• Providing approximately 55-60% of total calories as carbohydrates
• Maintaining glucose levels at moderate targets (140-180 mg/dL)
• Employing insulin therapy when needed to control hyperglycemia
• Limiting simple sugars while ensuring adequate complex carbohydrates

Managing carbohydrate intake to avoid excessive infusion rates (>5 mg/kg/min) helps reduce carbon dioxide production and minimize potential respiratory complications.

Lipid Requirements

Fats provide essential fatty acids and concentrated energy, with specific considerations in burn patients:

• Providing 20-25% of total calories as lipids
• Ensuring adequate omega-3 fatty acids to modulate inflammation
• Monitoring serum triglycerides to prevent hypertriglyceridemia
• Incorporating medium-chain triglycerides when malabsorption is present

Lipid emulsions for parenteral nutrition should include both long-chain triglycerides and omega-3 fatty acids to support immune function and wound healing while minimizing inflammatory responses.

Route of Nutritional Support

Enteral nutrition (EN) is the preferred route for nutritional support in burn patients whenever possible:

Enteral Nutrition

Benefits include:

• Preservation of gut mucosal integrity and barrier function
• Modulation of immune response
• Reduced infection risk compared to parenteral nutrition
• Lower cost and fewer complications

Initiation within 6-12 hours post-injury (or admission) when stable is recommended, even before surgical interventions. Early enteral feeding helps attenuate the hypermetabolic response and improves outcomes.

Parenteral Nutrition

Indicated when:

• Enteral access is not feasible
• Gastrointestinal function is significantly impaired
• Inadequate nutrition via enteral route despite maximum efforts
• Specific contraindications to enteral feeding exist

When parenteral nutrition is necessary, supplementing with minimal trophic enteral feeds (10-20 mL/hr) can help maintain gut integrity even if not meeting full nutritional requirements.

Vitamins and Minerals

Burn patients have increased requirements for numerous micronutrients due to accelerated losses and increased utilization:

Key Micronutrients

• Vitamin C: 500-1000 mg daily critical for collagen synthesis and wound healing
• Vitamin A: 10,000-25,000 IU daily supports epithelial growth and immune function
• Zinc: 20-40 mg daily essential for enzyme function, protein synthesis, and wound healing
• Copper: 2-4 mg daily important for cross-linking collagen
• Selenium: 200-400 mcg daily supports antioxidant defenses
• Vitamin D: 800-1000 IU daily may help modulate inflammation
• B vitamins: 2-3 times RDA important for energy metabolism

Trace elements should be included in all parenteral nutrition formulations and supplemented in enteral formulas when higher doses are needed.

Fluid and Electrolyte Management

Burn patients experience significant fluid shifts and electrolyte imbalances requiring careful monitoring:

• Adequate hydration to support wound healing and prevent hypovolemia
• Monitoring and correcting electrolytes, particularly sodium, potassium, phosphorus, and magnesium
• Adjusting fluid volumes based on insensible losses from burn wounds, fever, and ventilatory support
• Monitoring for signs of hypervolemia, especially during resuscitation phase

During the acute resuscitation phase, fluid management follows established burn formulas (e.g., Parkland, Brooke), with subsequent adjustments based on clinical response and ongoing losses.

Immunonutrition

Specific nutrients that modulate immune function may improve outcomes in burn patients:

• Arginine: 17-23 g/day supports wound healing and immune function
• Glutamine: 0.3-0.5 g/kg/day primary fuel for enterocytes and immune cells
• Omega-3 fatty acids: EPA/DHA 2-3 g/day modulates inflammation
• Nucleotides: Supports immune cell proliferation
• Antioxidants: Vitamin C, E, selenium reduces oxidative stress

Immunonutrition formulas containing combinations of these nutrients may reduce infection rates, shorten hospital stay, and improve wound healing, particularly in patients with burns >30% TBSA.

Pharmacological Interventions

Several pharmacological approaches can help modulate the hypermetabolic response:

• Oxandrolone: An anabolic steroid (10-20 mg twice daily) shown to improve lean body mass, wound healing, and shorten hospital stay
• Propranolol: Beta-blocker (1-2 mg/kg/day) reduces cardiac work, lipolysis, and resting energy expenditure
• Recombinant human growth hormone: May improve nitrogen balance, though concerns about hyperglycemia exist
• Insulin: Intensive insulin protocols to maintain moderate glycemia improve protein synthesis
• Metformin: May improve insulin sensitivity in long-term recovery

These interventions should be individualized based on patient characteristics and closely monitored for side effects.

Special Considerations

Pediatric Patients

Children have higher metabolic rates and smaller energy reserves, requiring:

• More aggressive nutritional support relative to body size
• Higher protein requirements per kilogram
• Increased carbohydrate needs to support brain development
• Formula selection appropriate for developmental stage
• Long-term growth monitoring after discharge

Elderly Patients

Older adults may experience:

• Reduced lean body mass reserves
• Decreased metabolic adaptation
• Potential for sarcopenia exacerbation
• Greater difficulty with oral intake
• Higher risk of complications

Pregnant Patients

Pregnant burn patients require:

• Increased protein and micronutrients to support fetal development
• Close monitoring of fetal well-being
• Balanced nutrition to support both maternal recovery and fetal growth

Post-Acute and Rehabilitation Phase

Nutritional needs continue during rehabilitation and scar remodeling:

• Gradual transition from specialized formulas to oral diet
• Continued high protein intake (1.5-2.0 g/kg/day) for wound healing and scar remodeling
• Maintenance of adequate energy to support increased activity
• Supplementation with vitamin C, A, zinc, and other wound-supporting nutrients
• Addressing potential eating difficulties and dysphagia
• Education on sustainable nutrition for long-term recovery

Scar tissue formation continues for up to 2 years post-burn, making ongoing nutritional support important during rehabilitation and outpatient follow-up.

Conclusion

Optimal nutrition therapy is a cornerstone of burn care, significantly affecting patient outcomes. The complex metabolic alterations induced by severe burns require systematic nutritional assessment, careful calculation of energy and protein needs, early enteral nutrition whenever possible, and appropriate supplementation.

Advancements in understanding the hypermetabolic response have led to evidence-based approaches that include targeted micronutrient supplementation, immunonutrition, and pharmacological modulation of catabolism. Individualized nutrition plans, regularly reassessed throughout the continuum of burn care, help maintain lean body mass, support wound healing, improve immune function, and ultimately enhance survival and quality of life for burn patients.

As research continues to elucidate the complex interactions between metabolism, nutrition, and recovery in burn patients, treatment approaches will continue to evolve, further improving outcomes for this vulnerable patient population.