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Hypothermia/Cold Injuries

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Topic updated on 11/01/16 2:38pm

Snapshot
  • EKG - Osborn waves in hypothermiaAn 87-year-old homeless military veteran is found unconscious in an alleyway in the middle of January. He was wearing a shirt, a sweater, a pair of pants, and a peacoat. He is brought by ambulance to the ED, where vitals are quickly obtained; his blood pressure is 100/50 mmHg, pulse is 50/min, and SaO2 is 92% on RA. Rectal temperature of 87.6°F (30.8°C) is measured. Naloxone was administered enroute by paramedics with no recovery of mental status. The patient is intubated and mechanically ventilated with warm humidifed O2. IV normal saline is infused at room temperature. Initial EKG monitoring reveals sinus bradycardia with no J-point variations or ST-T wave changes. A second EKG is completed and reveals the findings above. The trauma bay temperature is increased to 82°F (27.8°C). The patient's clothing is quickly cut and replaced with a dry blanket Bair Hugger. No evidence of cold injury is observed. Rectal temperature decreases to 85°F (29.4°C). The patient is transferred to the intensive care unit.
Introduction
  • Hypothermia is core temperature below 95°F (35°C)
    • mild: 90 - 95°F (32 - 35°C)
    • moderate: 82 - 90°F (28 - 32°C)
    • severe: < 82°F (< 28°C)
  • Mechanism of hypothermia depends on location
    • 4 mechanisms of heat loss
      • radiation - emission of electromagnetic energy
      • convection - transfer of heat to air or water
      • conduction - transfer of heat to solid object
      • evaporation - vaporization of water
    • radiation is main mechanism of heat loss in surgical setting (i.e. OR) due to increased exposure of body surface area
    • conduction/convection are main mechanisms of heat loss in accidental hypothermia
  • Cold-associated injuries along spectrum
    • frostnip
      • local paresthesia without permanent tissue injury
    • pernio
      • inflammatory lesion especially in cold and damp environment
    • immersion foot (nonfreezing cold injury)
      • inflammatory lesion with potential permanent tissue injury
    • frostbite (freezing cold injury)
      • inflammatory lesion due to intra- and extracellular ice crystal formation
        • requires debridement, antibiotics, tetanus vaccination
Presentation
  • Predisposing factors to hypothermia
    • age (particularly very young and very old)
    • lack of housing
    • drug overdose
    • alcohol ingestion
    • trauma
    • cold water immersion/sports
  • Symptoms and signs based on hypothermia severity
    • mild: tachycardia
      • normal mental status
      • + shivering
    • moderate: bradycardia, tachycardia with Osborn (J) waves on EKG
      • altered mental status
      • - shivering
    • severe: ventricular fibrillation/asystole, unconscious
    • arrhythmia is the most common cause of death from hypothermia
Evaluation and Management
  • Primary and secondary survey with resuscitation
    • if patient presents with cardiac arrest in setting of hypothermia:
      • best initial step: rewarm body
      • next step: ACLS algorithm based on arrhythmia (VFib / PEA )
        • however, if any pulse exists, do NOT perform CPR
        • do NOT treat new supraventricular arrhythmia pharmacologically
    • rewarming strategy is based on hypothermia severity, but goal is at least 0.9°F/hour
      • mild: passive external rewarming
        • elevate room temperature to 82°F (27.8°C)
        • remove wet clothes and replace with dry blanket
      • moderate: active external and internal rewarming
        • active external: warm blanket, warm bath
          • warm trunk before extremities to lower risk of "afterdrop" event
            • warming of extremities -> vasodilation -> cool blood moves from extremities to core -> cardiac arrest
        • active internal: warmed IV infusion and warmed, humidified oxygen
      • severe: same as for moderate hypothermia with possible extracorporal options
        • peritoneal and pleural irrigation with warmed fluids
        • cardiopulmonary bypass
        • peritoneal dialysis with warmed fluids
    • physical exam must document cardiovascular and neurological status, and evidence of cold-assciated skin injuries
  • Investigations
    • based on major complications of hypothermia, including coagulopathy, acidosis, arrhythmia, and FEN derangements
      • coagulation: CBC, PT/INR/PTT
      • acidosis: ABG, lactate
      • arrhythmia: 12-lead EKG
        • Osborn J-waves
          • distortion of early repolarization in V2-V5 at beginning of ST segment
          • can be confused for ischemic injury
          • not sensitive, specific, or prognostic
      • FEN: electrolytes, BUN/Cr, glucose, Ca2+, Mg2+
    • radiography
      • CXR may show evidence of aspiration pneumonia/pulmonary edema
  • Frostbite-specific management
    • immersion in 104-105°F (40 - 40.5°C) water for 10-30 minutes every day
      • provide pain medications!
    • cleaning and debridement
    • tetanus prophylaxis
    • NO prophylactic antibiotics

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