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Accidental Hypothermia - WMS Treatment Algorithm

Note: There is no standalone WMS "2024 update" specifically for hypothermia as of June 2026. The 2019 version remains the current WMS CPG. It is supplemented here by the 2025 ELSO ECMO guideline.

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STEP 0 - SCENE SAFETY & UNIVERSAL PRECAUTIONS

• Ensure rescuer safety first
• Prevent further cooling in ALL patients before any other intervention
• Remove from cold/wet environment; remove wet clothing gently
• Keep patient horizontal to avoid "rescue collapse" (orthostatic hypotension)
• Insulate with vapor barrier + sleeping bag/blanket (especially head, neck, trunk)

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SWISS STAGING SYSTEM (Clinical Field Diagnosis)

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STEP 1 - INITIAL ASSESSMENT (ALL PATIENTS)

1. Check for breathing and pulse for up to 60 seconds (hypothermia causes profound bradycardia and slow breathing - do not assume death prematurely)
2. Assess consciousness (GCS, verbal response)
3. Assess shivering (present, diminished, absent)
4. ECG/cardiac monitoring if available (look for J/Osborn waves, VF)
5. Core temp if equipment available (esophageal preferred; rectal acceptable)

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STAGE HT I - MILD (35-32°C)

• Handle gently; sit or lie down for at least 30 minutes
• Insulate with vapor barrier (especially head/neck) + sleeping bag
• Apply active external heat to axillae, chest, groin (chemical heat packs, warm water bottles - cover with cloth to prevent burns)
• Warmed, high-calorie food and drink if patient is alert and no aspiration risk
• Allow gentle exercise/movement if improving after warming period
• Evacuate if no improvement within 30 minutes or clinical deterioration

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STAGE HT II - MODERATE (32-28°C)

• Gentle handling is critical - sudden movement can precipitate VF
• Keep strictly horizontal
• No food or drink (aspiration risk)
• Full body insulation with vapor barrier
• Active external rewarming to trunk (axillae, chest, neck, groin) - avoid limbs to prevent "after-drop"
• Warm IV/IO fluids (43°C) if available
• Continuous cardiac monitoring - high risk for VF
• Supplemental warm humidified O2 if available
• Careful evacuation to hospital with rewarming capability

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STAGE HT III - SEVERE (28-24°C)

• Airway management: gentle orotracheal intubation if airway compromised (use caution - stimulation can trigger VF)
• Warm humidified O2 (42-46°C) via ventilator/BVM
• Warm IV fluids 43°C
• Cardiac instability: SBP <90 mmHg or HR <30 bpm = transfer immediately to ECLS-capable center
• VF management:
  • Attempt defibrillation up to 3 shocks
  • If VF persists, defer further shocks until core temp >30°C
  • Withhold epinephrine if Temp <30°C
  • If Temp >30°C: epinephrine every 6-10 minutes (extended interval vs. normothermic protocol)
• Urgent transfer to ECLS/ECMO-capable center

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STAGE HT IV - CARDIAC ARREST (<24°C)

CPR Decision:

CPR Protocol:

• Standard compression:ventilation ratio (30:2 or continuous with advanced airway)
• Continuous CPR during transport; use mechanical CPR device (e.g., LUCAS) if prolonged transport or difficult terrain
• Intermittent CPR (5 min on, 5 min off) only if continuous CPR is impossible

Drug Protocol:

ECMO/ECLS - PRIMARY REWARMING FOR HT IV:

• VA-ECMO (venoarterial) or cardiopulmonary bypass (CPB) is the preferred rewarming method for hypothermic cardiac arrest
• Rewarming rate: 4-10°C/hour
• Continue CPR throughout transport to ECLS center
• Transfer criteria: patient with hypothermic arrest, no non-survivable injury, potassium <12 mmol/L

Potassium as Futility Marker:

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STAGE HT V - DECLARE DEATH / WITHHOLD RESUSCITATION

• Serum potassium >12 mmol/L (cell lysis indicates lethal tissue damage)
• Non-survivable injuries (decapitation, chest crushed, rigor mortis with no hypothermia)
• Avalanche burial >60 minutes + in cardiac arrest + obstructed airway on extrication
• Prolonged asphyxia clearly preceding the hypothermia

Core WMS principle: "No one is dead until warm and dead" - a patient should not be pronounced dead until rewarmed to 30-35°C with persistent cardiac arrest.

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REWARMING METHODS SUMMARY

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KEY EVIDENCE UPDATES (2024-2025)

• ELSO 2025 (PMID: 41128452): Formalizes VA-ECMO as standard of care for hypothermic cardiac arrest in ECLS-capable centers; recommends continuous CPR during inter-hospital transport
• K+ >12 mmol/L remains the most robust futility marker (supported across WMS, ERC, ILCOR)
• Epinephrine withholding below 30°C is an important distinction from standard ACLS - drug metabolism is severely impaired and epinephrine can trigger VF
• Osborn/J-waves on ECG are pathognomonic of hypothermia but do not correlate with severity or predict VF
• Avalanche-specific: burial >60 min + arrest + airway obstruction = very poor prognosis; add K+ check before ECMO

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