16.2 Thermal Burns & Frostbite

16.2 Thermal Burns & Frostbite

Core Clinical Principle: Burns and frostbite are thermal injuries whose final depth is often not obvious on day one. Burn care depends on judging depth and size accurately, starting weight- and size-based fluid resuscitation for major burns, choosing topical agents by depth and location, and excising and grafting deep burns early. Frostbite care depends on rapid rewarming in warm water, early consideration of thrombolysis or iloprost for severe injuries, and patience: amputation waits until tissue clearly demarcates.

Wound specialists usually see these patients after initial resuscitation, when questions shift to depth reassessment, dressing selection, graft planning, scar control, and when to refer to a burn center. The American Burn Association referral criteria include partial-thickness burns over about 10% TBSA, any full-thickness burn, burns of the face, hands, feet, genitalia, perineum, or major joints, electrical and chemical burns, inhalation injury, and burns in patients with major comorbidities or in children at hospitals without pediatric expertise.

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Thermal Burns: Depth Assessment & Pathophysiology

Burn trauma produces acute coagulation necrosis of the skin and underlying tissues. Accurate assessment of burn depth is essential to determine fluid resuscitation requirements, predict scarring, and select reconstructive interventions.

Burn Depth Classification

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|                              JACKSON'S THREE ZONES OF THERMAL INJURY                            |
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| 1. ZONE OF COAGULATION (Central)                                                                |
|    • Point of maximum thermal contact; irreversible cellular protein denaturation and necrosis  |
|    • Completely non-viable tissue; requires surgical debridement or excision                    |
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| 2. ZONE OF STASIS (Intermediate)                                                                |
|    • Surrounds zone of coagulation; characterized by severe microvascular hypoperfusion        |
|    • Tissue is potentially salvageable, but exquisitely vulnerable to progressive ischemia,    |
|      hypotension, edema, and bacterial desiccation -> Converts to irreversible necrosis!       |
|    • TARGET OF RESUSCITATION: Timely IV fluids and topical antimicrobials prevent conversion   |
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| 3. ZONE OF HYPEREMIA (Outer Perimeter)                                                          |
|    • Peripheral zone of prominent vasodilatation driven by local inflammatory mediators        |
|    • High microvascular blood flow; tissue usually recovers unless sepsis or hypoperfusion occur |
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Burn Size Estimation: The Rule of Nines & Resuscitation Dynamics

Accurate quantification of total percentage of Total Body Surface Area (%TBSA) burned is required to guide systemic fluid administration. Only partial-thickness and full-thickness burns are included in the %TBSA calculation; superficial (first-degree) burns with erythema alone are excluded.

The Rule of Nines (Adult Patient)

• Head and Neck: 9% total (4.5% anterior, 4.5% posterior)
• Anterior Torso (Trunk): 18% (chest 9%, abdomen 9%)
• Posterior Torso (Trunk): 18% (upper back 9%, lower back/buttocks 9%)
• Each Upper Extremity: 9% each (entire right arm 9%, entire left arm 9%)
• Each Lower Extremity: 18% each (entire right leg 18%, entire left leg 18%; anterior leg 9%, posterior leg 9%)
• Perineum & Genitalia: 1%
• Palmar Method: The patient's entire palm (including fingers) represents approximately 1% of their TBSA, useful for assessing patchy or scattered burn distributions.

Burn Fluid Resuscitation Formulas (ATLS and Parkland)

In burns exceeding about 20% TBSA in adults, capillary leak produces hypovolemia and burn shock. The Advanced Trauma Life Support (ATLS, 10th edition) starting estimate for adult thermal burns is 2 mL lactated Ringer's × body weight (kg) × %TBSA over 24 hours (3 mL for children; 4 mL for high-voltage electrical injury). The historical Parkland formula used 4 mL:

$\text{Total 24-Hour Volume (mL of Lactated Ringer's)} = 4\text{ mL} \times \text{Weight (kg)} \times \%\text{TBSA}$

CRITICAL PARKLAND FLUID ADMINISTRATION TIMELINE
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1. FIRST 8 HOURS:
   • Administer exactly 50% (half) of the total calculated 24-hour volume within the
     first 8 hours calculated from the TIME OF INJURY (NOT the time of emergency
     department or clinic arrival!).

2. SUBSEQUENT 16 HOURS:
   • Administer the remaining 50% (half) of the calculated volume evenly over the
     next 16 hours.

3. CLINICAL TITRATION ENDPOINT:
   • The calculated volume is merely an initial guide! Fluid infusion rates MUST be
     titrated hourly to maintain an objective urine output:
     - Adult Target: about 0.5 mL/kg/hour (30 to 50 mL/hour).
     - Pediatric Target (≤30 kg): about 1 mL/kg/hour.
     - Over-resuscitation risks 'fluid creep' leading to pulmonary edema, extremity
       compartment syndrome, and abdominal compartment syndrome.
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Topical Antimicrobial Selection in Burn Management

Burn eschar is avascular, so systemic antibiotics reach it poorly and are not given prophylactically; topical antimicrobials and early excision are the main defenses against burn wound infection:

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Frostbite: Cold Thermal Trauma & Limb Salvage Protocols

Frostbite is a severe, localized cold thermal injury that occurs when tissue temperature drops below the freezing point (approximately -0.55°C / 31°F). It represents a dual pathophysiological injury: primary direct cellular freezing followed by secondary progressive microvascular thrombosis and reperfusion injury.

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|                        PATHOPHYSIOLOGICAL PHASES OF FROSTBITE INJURY                            |
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| 1. PRE-FREEZE PHASE & CELLULAR COOLING                                                          |
|    • Cutaneous vasoconstriction (sympathetic reflex) shunts blood away from extremities         |
|    • Endothelial cooling impairs active cellular transport and alters membrane permeability      |
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| 2. FREEZE-THAW (DIRECT CELLULAR) INJURY                                                         |
|    • Extracellular ice crystal nucleation begins in interstitial spaces                         |
|    • Osmotic fluid shift: Water is drawn from cells into interstitium -> Cellular dehydration   |
|    • Intracellular hyperosmolality + collapse -> Intracellular ice crystals form               |
|    • Mechanical shear and puncture of cell membrane and organelle lipid bilayers -> Cell death  |
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| 3. VASCULAR STASIS & THROMBOSIS (INDIRECT REPERFUSION INJURY)                                   |
|    • Thawing restores transient blood flow -> Delivers oxygen, generating toxic free radicals   |
|    • Severe endothelial cell necrosis, sloughing, and exposed subendothelial collagen            |
|    • Massive platelet aggregation, erythrocyte sludging, and fibrin microthrombi formation      |
|    • Release of potent vasoconstrictors: Thromboxane A2 (TxA2) and Prostaglandin F2α (PGF2α)     |
|    • Progressive microvascular occlusion -> Complete dermal capillary shutdown -> Wet/Dry Gangrene|
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Clinical Classification of Frostbite

Historically divided into four degrees analogous to burns, frostbite is now often described as superficial versus deep; the Cauchy classification grades severity after rewarming by the extent of cyanosis on the digits. The traditional degrees are:

Acute Resuscitation & Rapid Active Rewarming Protocol

The foundational intervention for acute frostbite is rapid active rewarming:

RAPID ACTIVE REWARMING PROTOCOL (STANDARD OF CARE)
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1. TIMING & FIELD CAUTION:
   • NEVER rewarm if there is ANY risk of REFREEZING during transport or evacuation!
     Walking on thawed frozen feet or undergoing a freeze-thaw-refreeze cycle causes
     severe mechanical and microvascular tissue injury that is worse
     than delayed thawing.
   • NEVER rub, massage, or apply snow to frostbitten tissue! Ice crystals mechanically
     shear, lacerate, and destroy fragile cellular architectures.

2. WATER BATH SPECIFICATIONS:
   • Submerge the affected limb in a circulating water bath maintained precisely at
     37°C to 39°C (98.6°F to 102.2°F), the range recommended by the Wilderness Medical Society.
   • Use an objective thermometer—do NOT rely on subjective touch! Temperatures >40-42°C
     induce thermal scald burn injury on insensate skin; temperatures <37°C prolong
     deleterious cold exposure.

3. DURATION & CLINICAL ENDPOINT:
   • Rewarming takes 15 to 30 minutes (up to 45 minutes for deep extremity freezes).
   • Continue immersion until the distal extremity thaws: skin becomes soft, pliable,
     and a bright erythematous flush (reperfusion flare) extends to digital tips.
   • Severe, excruciating reperfusion pain occurs during thawing; preemptive parenteral
     analgesia (for example, IV opioids) is needed.

4. DRY HEAT CONTRAINDICATION:
   • Slow rewarming (e.g., ambient room air, dry blankets) and dry direct radiant heat
     (campfires, car heaters, radiant lamps, heating pads) should be AVOIDED
     due to prolonged tissue ischemia, uneven heating, and devastating thermal burn risk.
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Microvascular Thrombolysis (tPA): The 24-Hour Window

In severe frostbite (Cauchy Grade 3 or 4, or deep injuries with hemorrhagic blisters, cyanosis, and absent digital perfusion), endovascular thrombosis rapidly produces irreversible tissue necrosis.

• Evidence & Mechanism: Intravenous or intra-arterial recombinant tissue plasminogen activator (tPA / alteplase) dissolves fibrin microthrombi within small digital vessels, restoring microcirculatory patency to ischemic beds.
• The Therapeutic Window: tPA is considered for severe frostbite within 24 hours of rewarming, and earlier treatment is associated with better salvage. After about 24 hours, benefit becomes unlikely because thrombosis and tissue injury are established.
• Protocol:
  • Vascular imaging (angiography or technetium-99m three-phase bone scan) is performed to document digital perfusion deficits.
  • tPA is given by catheter-directed intra-arterial infusion or by an intravenous protocol (institutional regimens vary, and systemic doses are capped), usually with heparin to reduce re-thrombosis.
  • In a retrospective comparison (Bruen et al., 2007), digital amputation occurred in about 10% of tPA-treated patients versus 41% of historical controls.
• Iloprost: Intravenous iloprost (Aurlumyn) was FDA-approved in February 2024 to reduce the risk of finger or toe amputation in adults with severe frostbite, and it is an alternative or adjunct when tPA is contraindicated.
• Contraindications: Presentation >24 hours post-thaw, concurrent major polytrauma, intracranial hemorrhage, active internal bleeding, or recent major surgery.

Delayed Amputation ("Frostbite in January, Amputate in July")

A central surgical principle in frostbite is avoiding premature debridement or early amputation:

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PRACTICE POINT: DELAYED AMPUTATION IN FROSTBITE
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"FROSTBITE IN JANUARY, AMPUTATE IN JULY!"

Early surgical excision of blackened, mummified frostbitten tissue should be
avoided unless infection forces it.

Pathophysiology of the Mummified Eschar:
  • Severe frostbite produces a dry, black, leathery, mummified carapace that
    acts as a protective biologic dressing.
  • Beneath this desiccated superficial shell, capillary neovascularization,
    collagen remodeling, and re-epithelialization proceed slowly from deep viable
    margins over 1 to 3 months (and up to 6 months).
  • Tissue that appears completely dead, black, and non-viable in week 2 frequently
    sheds as a superficial crust, revealing healthy, pink, viable dermis and functional
    pulp underneath.

Conservative Management Protocol:
  • Keep the eschar clean and dry; drain or debride clear blisters selectively
    and generally leave hemorrhagic blisters intact.
  • Apply non-adherent sterile dressings, dry gauze, and digital web separation.
  • Maintain strict elevation, avoid weight-bearing, and initiate physical therapy.
  • Allow spontaneous auto-amputation or elective delayed surgical amputation only
    after definitive, clear, anatomical demarcation between viable and non-viable
    tissue is fully established (typically 6 to 12 weeks post-injury).

EXCEPTIONS REQUIRING EARLY SURGERY:
  • Emergent debridement or open guillotine amputation is warranted ONLY if the
    patient develops acute invasive wet gangrene, suppurative tenosynovitis, or
    rapidly ascending systemic sepsis, or compartment syndrome requires fasciotomy.
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Clinical Traps

Trap 1: Counting Superficial Burns in %TBSA

Including areas of simple erythema inflates the calculated fluid volume and drives over-resuscitation ("fluid creep"). Count only partial- and full-thickness burns, then titrate to urine output rather than the formula.

Trap 2: Starting the 8-Hour Clock at Arrival

The first half of the 24-hour estimate is given in the first 8 hours from the time of injury. A patient who arrives 2 hours after the burn has only 6 hours left to receive that half.

Trap 3: Thawing Frostbite Before Evacuation

Thawing tissue that may refreeze during transport causes worse injury than staying frozen. Rewarm only when refreezing can be prevented, and never rub the tissue or use dry heat.