Wilderness Medicine

Hypothermia (Accidental): Treatment
Initial Steps (see also ACLS hypothermic algorithm)

• Assess scene
  • Hypothermia suspected
• Extricate patient from scene, protect from wind chill and further heat loss
  • Avoid rough handling and abrupt movements
  • Maintain horizontal position if able
  • Remove wet clothing
  • Apply dry clothing and/or insulating blankets
• Assess for responsiveness, airway, breathing, and circulation
  • Assess carotid or femoral pulse for up to 60 seconds before declaring pulseless
• Cardiac monitoring and core temperature measurement if able
• If obvious injury incompatible with life present, consider termination of resuscitation
  • Severe trauma with nonsurvivable injuries
  • Frozen solid, e.g., noncompressible torso, frozen airway

• Unresponsive or urgent airway protection needed?
  • Yes: intubate or place airway adjunct device if able
    • Warm, humidified oxygen
• Core temperature
  • ≥ 32 to 35°C: Mild hypothermia (Hypothermia I)
    • Provide warm environment and clothes, warm, sweet oral fluids if awake and able to swallow, and encourage movement/activity
    • If trauma, comorbidities, or altered mental status present treat as moderate hypothermia
  • ≥ 28 to 32°C: Moderate hypothermia (Hypothermia II)
    • Active external rewarming methods
      • Hot water bottles or chemical heat packs to neck, groin, axilla (insulate to avoid thermal burns)
      • Forced air warming system
    • Minimally invasive rewarming methods
      • Warm intravenous (IV) fluids (40°C)
    • Minimize movements to avoid dysrhythmias
  • < 28°C: Severe hypothermia (Hypothermia III)
    • Active external and minimally invasive rewarming methods as above
    • Transfer to hospital with extracorporeal life support (ECLS) capabilities is recommended due to risk of ventricular dysrhythmias and cardiac arrest
    • Transfer to nearest hospital if no ECLS within 6 hours
    • In-hospital, invasive rewarming methods:
      • Extracorporeal blood rewarming first line (V-V ECMO, V-A ECMO, cardiopulmonary bypass, hemodialysis)
      • Thoracic lavage
      • Peritoneal lavage
      • Bladder lavage
      • Gastrointestinal lavage

• Start CPR
• Secure airway
  • Heated, humidified oxygen
• Attach defibrillator pads and perform continuous cardiac monitoring
• Obtain intravenous (IV) or intraosseous (IO) access
• Core temperature
  • < 30°C:
    • Continue chest compressions
    • Ventricular fibrillation (VF) or ventricular tachycardia (VT): perform up to a maximum of 3 defibrillation attempts, if still in VF or VT withhold further shocks until core temperature > 30°C
    • Pulseless electrical activity (PEA) or asystole: epinephrine and other IV meds not recommended until core temp > 30°C; if epinephrine given recommend increasing dosing interval from every 3-5 minutes to every 6-10 minutes
      Rewarm using invasive and external rewarming techniques
  • ≥ 30 to 32°C:
    • Continue chest compressions and defibrillation if indicated according to ACLS protocols
    • Consider increasing the interval between medication dosing due to peripheral vasoconstriction
    • Rewarm using invasive and external rewarming techniques
  • ≥ 32°C: continue CPR according to ACLS/PALS protocols, consider termination of resuscitation if no improvement
• Continue active rewarming until core temp ³ 32°C
• Transfer to hospital with ECLS capabilities
• Monitor for hypoglycemia and treat with dextrose as needed
• Consider hyperkalemia treatments (calcium, bicarbonate, dextrose and insulin) as rewarming occurs or in cases of crush injury, compartment syndrome, or prolonged immobilization
• Follow standard post-ROSC procedures according to institutional protocols

• Cardiac arrest
• Core temperature < 30°C
• Systolic blood pressure < 90 mmHg
• Ventricular dysrhythmia

• Peripheral pulses may be difficult to palpate due to vasoconstriction
• Decreases in heart rate and blood pressure are expected physiological responses to hypothermia, and treatment should focus on rewarming if pulses are present
• Muscular rigidity may mimic rigor mortis but is not a reliable sign of death in a severely hypothermic patient
• Central nervous system depression occurs as hypothermia severity worsens and may manifest as altered mental status, ataxia, areflexia, or loss of pupillary and corneal reflexes. Neurological impairment is not a reliable indicator of prognosis while hypothermic.
• As rewarming occurs, IV fluid requirements may increase due to vasodilation and dehydration from cold-induced diuresis
• Afterdrop, a paradoxical decrease in temperature after rewarming is initiated, may occur due to increased circulation of colder, peripheral blood
• Rescue collapse (cardiac arrest that occurs during extrication or transport) may occur and may involve multifactorial processes including hypovolemia, myocardial irritability leading to dysrhythmia, and metabolic derangements

• Unable to provide continuous chest compressions
  • Consider alternating periods with and without CPR if severe hypothermia present
  • Core temperature < 28°C
    • Alternate 5 minutes of CPR and ≤ 5 minutes without CPR
  • Core temperature < 24°C
    • Alternate 5 minutes of CPR and ≤ 10 minutes without CPR
• Children
  • Prolonged resuscitation may be indicated as children are more likely to tolerate hypoxic brain insult than adults, and good neurological outcomes have been reported after prolonged CPR
• Drowning
  • Cardiac arrest after submersion unlikely to benefit from prolonged resuscitation
    • Cardiac arrest is most often due to hypoxia while normothermic and brain death occurs prior to hypothermia
    • However, cases have been reported in both adults and children involving submersion injuries with hypothermia and cardiac arrest that resulted in survival with favorable neurologic outcome
  • Cardiac arrest after immersion (trapped in cold water but able to breath) more likely to have a good outcome after prolonged resuscitation
    • Cardiac arrest presumably due to hypothermia rather than hypoxia
• Avalanche burial
  • Hypothermia will likely take at least 35 minutes to develop after avalanche burial
  • Cardiac arrest after avalanche burial more often due to trauma or asphyxia than hypothermia
  • Patient in cardiac arrest recovered after < 35 minutes of avalanche burial unlikely to benefit from prolonged resuscitation
  • If suspected hypothermic cardiac arrest after ³ 35 minutes of burial and no obvious trauma or asphyxiation (snow-packed airway) it is reasonable to pursue rewarming and prolonged resuscitative efforts

1. Auerbach, Paul S., Benjamin B, et al. Field Guide to Wilderness Medicine. Fifth edition. Philadelphia: Elsevier, 2019.
2. Paal P, Pasquier M, Darocha T, et al. Accidental Hypothermia: 2021 Update. Int J Environ Res Public Health. 2022;19(1):501.
3. Paal P, Gordon L, Strapazzon G, et al. Accidental hypothermia-an update : The content of this review is endorsed by the International Commission for Mountain Emergency Medicine (ICAR MEDCOM). Scand J Trauma Resusc Emerg Med. 2016;24(1):111.
4. Vanden Hoek TL, Morrison LJ, Shuster M, et al. Part 12: cardiac arrest in special situations: 2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation. 2010;122(18 Suppl 3):S829–61.
5. Brown DA. Hypothermia. In: Tintinalli JE, Ma O, Yealy DM, Meckler GD, Stapczynski J, Cline DM, Thomas SH. eds. Tintinalli's Emergency Medicine: A Comprehensive Study Guide, 9e. McGraw Hill; 2020.

1. Binckley, Shannon, MD
2. Portouw, Steven, MD, FAAEM, FAWM