Updated: 4/10/2017

Frostbite

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Introduction
  • Definition
    • extensive soft tissue damage associated with exposure to temperatures below freezing point
  • Epidemiology
    • demographics
      • males (m:f = 10:1)
      • age 30-50 years
    • risk factors
      • host factors
        • alcohol abuse
        • mental illness
        • peripheral vascular disease
        • peripheral neuropathy
        • malnutrition
        • chronic illness
        • tobacco use
        • race
          • African descent more likely to sustain frostbite than Caucasians who have better cold induced vasodilatation
        • smoking
          • reduces nitric oxide (vasodilator)
          • potentiates thrombosis by increasing fibrinogen levels and platelet activity
      • environmental factors
        • degree of cold temperature
          • risk of frostbite is low at > -10°C
          • risk of frostbite is high at < -25°C
        • duration of exposure
        • windchill
          • tissues at -18°C freeze in 1h at windspeed of 10mph
          • tissues at -18°C freeze in 10min at windspeed of 40mph
        • altitude >17,000 feet
        • contact with conductive materials (water, ice, metal)
  • Pathophysiology
    • with hypothermia (CBT <35°C) circulation shunted from periphery to maintain core body temperature (CBT)
    • cardiac effects
      • basal metabolic rate, HR and cardiac output drop
      • myocardial irritability (abnormal EKG)
    • neurological effects
      • disorientation, coma
      • shivering (anaerobic) until CBT drops below 30-32°C
      • below 30-32°C, shivering stops and muscle rigidity ensures (like rigor mortis)
        • resembles death (absent respirations, dilated pupils, muscle rigidity)
        • must be rewarmed before pronounced dead (“no one is dead until warm and dead”)
    • limbs (4 phases)
      • phase I (cooling and freezing)
        • vasoconstriction/vasospasm followed by transient arteriovenous shunting (hunting response) of cycles of vasodilatation/vasoconstriction every 10min
          • those who do not have this response are more prone to cold injury
          • with persistent cold, cycles cease and temperature in tissue drops to freezing point of tissue (<-2°C)
          • ice crystals
            • extracellular ice crystals causes sludging/stasis and intracellular dehydration (because of osmotic gradient)
            • intracellular ice crystals destroy cell membranes
          • interstitial crystallization is exothermic, maintains latent heat to keep limb above freezing temperature
          • when crystallization is complete, limb temperature falls to ambient temperature
      • phase II (rewarming)
        • reverses freezing process
        • limb absorbs heat, intra/extracellular ice crystals melt
        • intracellular swelling occurs
        • endothelial cells of capillaries become permeable
          • fluid extravasation leads to blisters/edema
          • important to prevent re-freezing (freeze-thaw has severe effects on tissues)
      • phase III (progressive tissue injury)
        • inflammation, stasis/thrombosis, tissue necrosis
        • diminished prostaglandin E2 (vasodilator, antiplatelet)
        • elevated prostaglandin F2a and thromboxane B2 (vasoconstrictors, platelet-aggregating)
    • phase IV (resolution)
      • complete healing with no symptoms
      • healing with sequelae
      • early tissue necrosis/gangrene
    • cell biology
      • leads to movement of water from intracellular location to extracellular location 
      • cellular dehydration leads to cell death
    • biochemistry
    •  
      •  ice crystal formation occurs within the extracellular fluid at -2 to -15°C
      • sensory nerve dysfunction occurs at -10°C
  • Associated conditions
    • frostnip
      • mildest cold exposure injury
      • only affects superficial layers of skin (blanching, numbness) but no dermis damage
      • reversible
    • chilblain (pernio)
      • occurs in cold, nonfreezing temperatures in dry conditions
      • burning sensation, with pruritus, swelling, erythema
      • may have blisters, ulceration
      • resolves in 2 weeks
      • may leave chronic vasculitis esp in young/middle-aged women
    • trench foot (immersion foot)
      • military personnel
      • prolonged wet nonfreezing condition <10°C
    • frostbite   
      • results in localized/extensive tissue necrosis
      • may require amputation
    • hypothermia
      • when core body temperature is affected
      • can be fatal
  • Prognosis
    • the severity is increased with
      • alcohol consumption/intoxication
      • contact of skin with metal or ice
      • elevated wind chill factor
Presentation
  • Physical exam
    • hypothermia (mild, 32-35°C; moderate, 28-32°C; severe, <28°C)
      • tachycardia followed by bradycardia, decreased cardiac output, arrythymia (atrial and ventricular fibrillation)
      • decreased respiratory rate
        • CO2 retention leads to hypoxia/respiratory acidosis
      • disorientation, comatose
    • frostbite (similar to burns)
      • traditional classification
        • 1st degree – central whitish area with surrounding erythema
        • 2nd degree – clear/cloudy blisters within 24h
        • 3rd degree – hemorrhagic blisters / hard black eschars
        • 4th degree – tissue necrosis
      • newer classification
        • superficial (1st and 2nd degree) has good prognosis
        • deep (3rd and 4th degree) has poor prognosis
      • blisters form 6-24 hours after rewarming
        • superficial lesions present as clear blisters 
        • deeper lesions form hemorrhagic blisters which may be painless 
Imaging
  • MRI
    • T2-weighted images shows enhanced signal in necrotic muscles because of disrupted cell membranes and increased extracellular fluid
  • Serial bone scans (99mTc)  
    • can be used to evaluate the severity of the soft-tissue damage
    • 1st scan at 2 days after initial injury
      • absence of uptake has poor prognosis but may not indicate necrosis
    • 2nd scan at 5 days after initial injury
      • normal blood/bone pool = treat expectantly
      • diminished blood/bone pool = observation, with potential early debridement
      • absent blood/bone pool = early debridement or amputation
Treatment for Hypothermia
  • protect patient from further exposure to freezing temperature
  • rewarming 
    • only after confirmation that the patient can be maintained in a constant warm environment (avoid freeze-thaw cycles)
    • external-surface rewarming (for mild hyperthermia)
      • passive
        • dry clothes and warm room
      • active
        • disadvantage is too-rapid vasodilatation leads to metabolic waste rushing to core, leading to paradoxical drop in core temperature (“afterdrop”) that can worsen arrythmia
        • heat lamps, radiant heaters, heating blanket, immersion in warm water with cardiac monitoring
    • internal-core rewarming (for moderate and severe hypothermia)
      • warmed oxygen, warm IV fluid
      • body cavity lavage (invasive)
      • cardiac bypass
        • requires systemic heparinization
      • continuous arteriovenous rewarming
        • blood from femoral arterial catheter into fluid heat exchanger
        • returns to body through subclavian venous catheter
        • achieves 1°C every 15min
    • avoid alcohol/sedatives
      • dulls shivering response and further lowers CBT
Treatment for Frostbite
  •  Nonoperative
    • prevention  
      • footwear thermal insulation is the most important factor for protection against cold induced injury
    • protect limb from mechanical trauma e.g. walking, rubbing
      • pad/splint, wrap with blanket for transportation
    • initial resuscitation with warm IV fluids, tetanus prophylaxis, NSAIDS, silver sulfadiazine ointment or topical antibiotics to open wounds, rapid rewarming
      • indications
        • superficial frostbite
      • water bath 40-42°C with mild antibacterial agent x 30min
        • successful when skin becomes pliable and red-purple
        • avoid repetitive freeze-thaw cycles
      • IV analgesia / conscious sedation
      • wound care with topical aloe vera, extremity elevation and splinting 
    • IV antibiotics
      • if secondarily infected
    • rehabilitation
      • whirlpool hydrotherapy
      • PT and OT for preserve joint motion
  • Adjunctive (low molecular weight dextran, anticoagulants, tissue plasminogen activator)
    • intravenous tPA within 24h reduces rate of digital amputations
      • indications
        • no blood flow on bone scan
        • 2nd or 3rd degree (NOT superficial frostbite)
      • contraindications
        • general contraindications
          • alcoholic patients (risk of bleeding from concomitant head injuries)
          • active internal bleeding
          • intracranial hemorrhage/surgery within past 3 months 
          • concurrent trauma
          • major surgery within previous 14 days
          • known aneurysm or vascular malformation
          • known bleeding diathesis
          • pregnancy
          • labile hypertension 
        • cold-related contraindications
          • > 24 hours of cold exposure
          • warm ischemia times >6h 
          • multiple freeze-thaw cycles
    • hyperbaric oxygen (anecdotal evidence)
  • Operative
    • immediate surgical escharotomy
      • circumferentially constrictive lesion of digit
    • fasciotomy 
      • for compartment syndrome
    • debride clear blisters and apply aloe vera
      • reduces high levels of prostaglandin F2 and thromboxane B2
    • drain/aspirate hemorrhagic blisters (represents deep injury) but leave intact  
      • prevents dessication of underlying dermis
    • late debridement/amputation for necrosis
      • “frostbite in January, amputate in July”
      • after demarcation occurs at 1-3months  
    • surgical sympathectomy
      • reduces duration of pain and time to demarcation of tissue
      • does not reduce extent of necrosis
Complications
  • Adults
    • persistent pain (50%)
      • intolerable in 15%
    • cold intolerance
    • vasospastic disease (Raynauds phenomenon, cold sensitivity, persistent color changes, hyperhidrosis)
      • treatment
        • calcium channel blockers, vasodilators, beta blockers, surgical sympathetectomy
          • indications
            • late, persistent vasospastic disease 
    • neuropathy (cold/heat hypersensitivity, hypesthesia, paresthesia)
      • decreased motor/sensory NCV
      • treatment
        • decompression e.g. carpal tunnel release
    • musculoskeletal (osteopenia)
      • subchondral bone loss (frostbite arthropathy), joint contractures esp in DIPJ > PIPJ of hands and feet
      • treatment
        • joint arthroplasty, resection arthroplasty
  • Children
    • premature growth plate closure
      • 1-2 years after exposure
      • secondary to chondrocytic injury
    • joint laxity, angular deformities, short digits, excess skin, degenerative joint changes
      • seen after age 10 in patients with prior frost bite injuries
      • treatment
        • physeal arrest, osteotomy, arthrodesis
 

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(OBQ12.26) A 22-year-old college student presents with significant finger pain after coming into contact with liquid nitrogen in his chemistry lab. A clinical photo of the affected finger in shown in Figure A. What is the most appropriate next step in treatment? Review Topic

QID: 4386
FIGURES:
1

Blister debridement and hyperbaric oxygen therapy

6%

(314/5295)

2

Drainage of the blister with the overlying skin left intact

54%

(2853/5295)

3

Full thickness blister and skin debridement with local flap coverage

15%

(779/5295)

4

MRI scan of the digit to assess degree of soft tissue damage

9%

(455/5295)

5

Wet to dry twice-daily dressing changes to the digit

16%

(860/5295)

L 4

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