How does the pathophysiology of burn injury relate to fluid resuscitation?

Burn Injury Pathophysiology and Fluid Resuscitation

Severe burn injuries require immediate fluid resuscitation with balanced crystalloids such as Lactated Ringer's solution at 20 mL/kg in the first hour to address the pathophysiological changes of burn shock and reduce morbidity and mortality. 1

Pathophysiology of Burn Shock

Burn injury triggers a cascade of pathophysiological changes that necessitate prompt fluid resuscitation:

• Immediate vascular changes:

  • Severe burn injuries induce early hypovolemic shock due to inflammation, capillary leak syndrome, and alterations in the microcirculation 2
  • The nadir of cardiac output appears within the first 4 hours post-injury 2
  • Massive fluid shifts occur from intravascular to interstitial spaces due to increased capillary permeability
  • Endothelial glycocalyx layer damage ("burn endotheliopathy") is a key mechanism in burn shock pathophysiology 3

• Systemic inflammatory response:

  • Release of inflammatory mediators causes vasodilation
  • Increased vascular permeability leads to protein-rich fluid extravasation
  • Edema formation in both burned and non-burned tissues

Fluid Resuscitation Approach

Initial Resuscitation

• First hour management:
  • Administer 20 mL/kg balanced crystalloid solution in the first hour, regardless of visible burn area 1
  • Adults with ≥15% total body surface area (TBSA) burns and children with ≥10% TBSA require this immediate fluid bolus 2
  • Establish IV access in unburned areas when possible 1

Ongoing Resuscitation

• Formula-based approach:

  • Use Parkland formula as a starting point (2-4 mL/kg/%TBSA for first 24 hours) 1
  • Children require higher fluid volumes (approximately 6 mL/kg/%TBSA) due to higher body surface area/weight ratio 1
  • Half of calculated 24-hour volume given in first 8 hours post-burn, remainder over next 16 hours

• Fluid choice:

  • Balanced crystalloids are recommended as first-line fluid 2, 1
  • Lactated Ringer's solution is preferred due to its electrolyte composition being closer to plasma 2
  • Normal saline should be avoided as primary resuscitation fluid due to risk of hyperchloremic metabolic acidosis and acute kidney injury 2
  • Special considerations:
    • Normal saline is preferred in patients with traumatic brain injury to maintain plasma osmolality 1
    • Hartmann solution should be avoided in patients with crush syndrome or rhabdomyolysis due to potassium content 1

Monitoring and Endpoints

• Primary endpoints:

  • Hourly urine output: 0.5-1 mL/kg/hour in adults, 1-2 mL/kg/hour in children 1
  • Higher urine output (1-2 mL/kg/hour) needed with myoglobinuria 1

• Additional monitoring:

  • Arterial lactate concentration
  • Hemodynamic parameters
  • Echocardiography when available

Avoiding Complications

Under-resuscitation Risks

• Organ hypoperfusion
• Multiple organ dysfunction
• Death

Over-resuscitation ("Fluid Creep") Risks

• Respiratory failure
• Compartment syndromes (abdominal, extremity)
• Excessive edema formation
• Increased morbidity and mortality 4

Balanced Approach

• Titrate fluid to clinical response rather than rigidly following formula calculations 1
• Goal: Provide the least amount of fluid necessary to maintain adequate organ perfusion 4
• Monitor for intra-abdominal hypertension, which may require escharotomy within 48 hours if circulatory impairment occurs 2

Special Considerations

• Albumin use:

  • Consider albumin administration after the first 24 hours post-burn to maintain plasma colloid osmotic pressure 5
  • Aim to maintain plasma albumin concentration around 2.5 ± 0.5 g/100 mL 5

• Adjunctive therapies:

  • High-dose ascorbic acid has been investigated to limit fluid requirements, though results are mixed 3
  • Plasma administration is being studied as an alternative resuscitation strategy 3

The pathophysiological understanding of burn shock has evolved significantly, leading to improved resuscitation strategies that balance the need for adequate organ perfusion while minimizing the complications of excessive fluid administration. Modern approaches focus on personalized fluid management rather than rigid formula-based protocols.