Hypothermia Summary

Classification

  • Mild: 32-35°C (conscious, shivering)
  • Moderate: 28-32°C (impaired consciousness)
  • Severe: <28°C (unconscious)
  • Cardiac arrest: <24°C

Key Principles

  • Check for signs of life for up to 1 minute
  • "No one is dead until warm and dead"
  • Handle gently to prevent VF
  • Consider afterdrop during transport

ALS Modifications

  • Withhold drugs until ≥30°C
  • Double drug intervals at 30-35°C
  • Defibrillate per protocol
  • If VF persists after 3 shocks, delay until ≥30°C

Rewarming Strategy

  • Stage I: Passive external
  • Stage II-IV: Active external + internal
  • Severe: Consider ECLS if K+ <8 mmol/L
  • VA-ECMO preferred method

ECG Findings

  • Osborne (J) waves
  • Prolonged intervals
  • Bradycardia
  • Arrhythmias

Complications

  • Cardiac arrhythmias
  • Infection/pneumonia
  • Coagulopathy
  • Electrolyte abnormalities

Critical Points

  • Use low-reading thermometer
  • Avoid hyperthermia during rewarming
  • Large IV fluid volumes needed
  • Consider HOPE/ICE scores for prognosis

Hypothermia

Comprehensive guide to classification, diagnosis, and management of accidental hypothermia

Definition and Classification

Hypothermia is defined as a body core temperature below 35°C. Early recognition and appropriate management are crucial for patient survival.

Temperature-Based Classification

Severity Temperature Range Clinical Features
Mild 32 - 35°C Conscious, shivering, alert
Moderate 28 - 32°C Impaired consciousness, no shivering
Severe < 28°C Unconscious, vital signs present
Cardiac Arrest < 24°C No or minimal vital signs
Irreversible < 13.7°C Death due to irreversible hypothermia

Swiss Staging System

Stage I

  • Mild hypothermia
  • Conscious, shivering
  • Core temperature 32-35°C

Stage II

  • Moderate hypothermia
  • Impaired consciousness without shivering
  • Core temperature 28-32°C

Stage III

  • Severe hypothermia
  • Unconscious, vital signs present
  • Core temperature 24-28°C

Stage IV

  • Cardiac arrest or low flow state
  • No or minimal vital signs
  • Core temperature < 24°C

Stage V

  • Death due to irreversible hypothermia
  • Core temperature < 13.7°C

Diagnosis

Accidental hypothermia may be under-diagnosed in countries with a temperate climate. When thermoregulation is impaired (e.g., elderly and very young) hypothermia may follow a mild insult.

Risk Factors

Temperature Measurement

Recommended Methods

  • Lower third of esophagus (correlates well with heart temperature)
  • Tympanic measurement using thermocouple (reliable alternative)

Not Recommended

  • Bladder and rectal temperatures (lag behind core temperature)
  • Infrared tympanic thermometers (not designed for low temperatures)

Note: Once in hospital, use a consistent core temperature measurement site throughout resuscitation and rewarming.

Decision to Resuscitate

"No one is dead until warm and dead" - Cooling decreases cellular oxygen consumption by about 6% per 1°C decrease in core temperature, providing protective effects on the brain and vital organs.

Key Principles

When to Withhold CPR (Prehospital)

CPR should only be withheld if:

  • Clear signs of lethal injury or irreversible death
  • Valid DNACPR decision
  • Conditions unsafe for rescuer
  • Avalanche burial ≥ 60 min and airway packed with snow and asystole

ALS Modifications in Hypothermia

Initial Assessment

Modified Approach
  1. Check for signs of life for up to 1 minute
  2. Palpate a central artery and assess cardiac rhythm
  3. If any doubt, start CPR immediately
  4. Do not delay careful tracheal intubation where indicated
  5. Once CPR underway, confirm hypothermia with low-reading thermometer

Drug Administration

Temperature Drug Protocol
< 30°C Withhold adrenaline and other CPR drugs
30-35°C Double intervals between drug doses (adrenaline every 6-10 minutes)
≥ 35°C Apply standard drug protocols

Defibrillation Protocol

  • If VF detected, defibrillate according to standard protocols
  • If VF persists after 3 shocks, delay further attempts until core temperature ≥ 30°C
  • CPR and rewarming may have to be continued for several hours
  • Use HOPE or ICE scores for prognostication

Rewarming Strategies

General Principles

All Patients

  • Remove from cold environment
  • Prevent further heat loss
  • Rapid transfer to hospital
  • Handle carefully to prevent VF

Special Considerations

  • Remove wet clothes while minimizing movement
  • Patients with mild hypothermia can mobilize
  • Beware of afterdrop during transport
  • Non-shivering patients cool faster

Rewarming Techniques

Passive External Rewarming

  • Remove wet clothes and dry body
  • Mobilize conscious individuals
  • Full body insulation
  • Warm environment

Active External Rewarming

  • Warm blankets
  • Heating pads
  • Warm baths
  • Forced warm air (Bair Hugger)

Active Internal Rewarming

  • Warm intravenous fluids
  • Warm humidified oxygen
  • Peritoneal lavage
  • Extracorporeal life support (ECLS)

ECLS Indications

Consider ECLS rewarming where available for:

  • Core temperature < 32°C AND
  • Potassium < 8 mmol/L

Veno-arterial ECMO (VA-ECMO) is the preferred method.

ECG Changes in Hypothermia

Characteristic ECG findings in hypothermia include prolonged intervals, bradycardia, and distinctive Osborne waves.

Common ECG Findings

Osborne Wave

The Osborne wave (also called J wave) is a distinctive electrocardiographic finding seen in hypothermia, appearing as a positive deflection at the junction between the QRS complex and ST segment.

Complications

Cardiac

  • Cardiac arrhythmias (<30-32°C)
  • Ventricular fibrillation
  • Asystole

Respiratory

  • Aspiration pneumonia
  • Pulmonary edema
  • Respiratory failure

Other Complications

  • Infection
  • Pancreatitis
  • Bleeding diathesis/coagulopathy
  • Bladder atony
  • Frostbite
  • Electrolyte abnormalities (hyperkalemia, hypoglycemia)

Post-Resuscitation Care

  • Continuous hemodynamic monitoring essential
  • Large volumes of IV fluids required during rewarming
  • Avoid hyperthermia during and after rewarming
  • Once ROSC achieved, use standard post-resuscitation care