What is the recommended assessment and management for a patient presenting with hypothermia, including severity classification, rewarming methods, hemodynamic support, and treatment of arrhythmias?

Hypothermia Assessment and Management

Severity Classification

Hypothermia classification must be based on core body temperature measurement, not clinical presentation alone, as symptoms can be misleading. 1

Temperature-Based Classification

• Cold stress (35-37°C): Alert patient, possibly shivering 2
• Mild hypothermia (32-35°C): Altered responsiveness, shivering present 2
• Moderate hypothermia (28-32°C): Decreased responsiveness, shivering may be absent, bradycardia develops 2
• Severe hypothermia (<28°C): Unresponsive, appears lifeless, high risk for ventricular fibrillation 2, 3
• Profound hypothermia (<24°C): Cessation of shivering, slow heart rate and breathing, extreme cardiac instability 2

Trauma-Specific Classification

For trauma patients, use slightly different thresholds: mild (34-36°C), moderate (32-34°C), severe (<32°C), as even mild hypothermia significantly increases mortality from 7% to 43% 2, 3

Temperature Monitoring

Use esophageal or bladder thermometry with a low-reading thermometer capable of measuring below 35°C for accurate core temperature assessment. 3, 4

• Oral probes are acceptable alternatives when properly placed in the sublingual pouch 2, 4
• Tympanic infrared probes may be used when oral measurement is not feasible 4
• Avoid axillary measurements as they read 1.5-1.9°C below actual core temperature 4
• Pulmonary artery catheters are most accurate but impractical in most settings due to complications 2

Initial Management: All Severity Levels

Immediately remove the patient from cold environment, remove all wet clothing, and protect from further heat loss using insulation from ground, head/neck covering, and wind shielding with plastic or foil layers plus dry insulating blankets. 2

Rewarming Strategies by Severity

Cold Stress and Mild Hypothermia (32-35°C)

Use passive rewarming with blankets combined with active external rewarming methods. 2, 4

• Move to warm environment and allow passive rewarming 2
• Apply forced-air warming blankets, heating pads, or radiant heaters 4
• Provide high-calorie foods or drinks if patient is alert and can safely swallow 2
• Monitor for deterioration and protect from falls due to altered responsiveness 2, 4

Moderate Hypothermia (28-32°C)

This is a medical emergency requiring activation of emergency response system, gentle handling to avoid triggering arrhythmias, and aggressive active rewarming using all available methods. 2

• Continue all measures for mild hypothermia 4
• Apply forced-air warming blankets (increases rewarming rate to 2.4°C/hour vs 1.4°C/hour with passive methods) 4
• Administer warmed intravenous isotonic crystalloid 3, 4
• Provide humidified, warmed oxygen 4
• Handle patient gently to prevent arrhythmia precipitation 2
• Never use cold IV fluid boluses in accidental hypothermia 4

Severe and Profound Hypothermia (<28°C)

Requires active core rewarming methods in addition to all external rewarming measures, with consideration of invasive strategies. 3, 4

• Continue all measures for moderate hypothermia 4
• Consider body cavity lavage (peritoneal, thoracic, bladder) with warmed fluids 5, 6
• Consider extracorporeal rewarming (hemodialysis achieves 1.9°C/hour rewarming rate, ECMO for cardiac arrest) 6, 7
• Activate emergency response system immediately 2, 4
• Handle extremely gently as severe hypothermia carries 84.9% mortality risk 3

Rewarming Device Safety

Place insulation between any heat source and skin, follow manufacturer instructions, and frequently monitor for burns and pressure injuries. 2

Rewarming Targets

Target a minimum core temperature of 36°C before considering the patient stable, but cease active rewarming at 37°C as higher temperatures are associated with increased mortality. 3, 4

• Monitor core temperature every 5-15 minutes depending on severity 4
• Watch for rewarming shock, rebound hyperthermia, and electrolyte abnormalities 4

Cardiac Arrhythmia Management

Defibrillation Approach

If ventricular fibrillation or ventricular tachycardia is present, attempt defibrillation immediately regardless of temperature. 2

• After initial shock, it is reasonable to perform further defibrillation attempts according to standard ACLS algorithm concurrent with rewarming 2
• The hypothermic heart may respond better to defibrillation than previously believed, with animal studies showing successful defibrillation at temperatures as low as 30°C 2

Medication Use

Consider using vasopressors (epinephrine or vasopressin) during cardiac arrest even in severe hypothermia, as animal studies show 62% ROSC vs 17% with placebo. 2

• Previous recommendations to withhold medications below 30°C are being challenged by newer evidence 2
• Antiarrhythmic medications have not shown benefit in hypothermic arrest 2
• Be aware of potential drug accumulation due to reduced metabolism 2

Bradycardia Management

Monitor bradycardia but recognize it may be physiologically beneficial during hypothermia; avoid aggressive treatment unless hemodynamically unstable. 4

Hemodynamic Support

Administer warmed isotonic crystalloid intravenously for volume resuscitation in moderate to severe hypothermia. 3, 4

• Hypothermia causes impaired diastolic relaxation and cardiovascular compromise even at mild levels 3
• Monitor for coagulopathy as hypothermia impairs platelet function 3, 4
• Watch for rewarming shock during active rewarming 4

Special Considerations

Cardiac Arrest

If the hypothermic patient has no signs of life, begin CPR immediately without delay. 2

• Pulse may be slow or difficult to detect 2
• Continue resuscitation efforts during rewarming as profound hypothermia patients have survived with good neurologic outcomes 2
• After ROSC, continue warming to 32-34°C and maintain according to standard post-arrest guidelines 2

Hypothermia Wrap Technique

For patients with decreased responsiveness wearing damp (not saturated) polyester fleece who cannot be moved to warm environment, use hypothermia wrap technique with chemical heat blankets, plastic/foil layers, and insulative blankets. 2

Body-to-Body Rewarming

Do not use body-to-body rewarming as it is not beneficial over other active rewarming techniques such as chemical heat packs or forced air systems. 2

Critical Pitfalls to Avoid

• Never rely on clinical presentation alone for severity classification—a patient can appear alert with severe hypothermia (core temperature 25°C) 1
• Never use axillary temperature measurements as they significantly underestimate core temperature 4
• Never rewarm above 37°C as hyperthermia worsens outcomes 3, 4
• Never handle moderate-to-severe hypothermia patients roughly as this can precipitate fatal arrhythmias 2
• Never use passive rewarming alone for temperatures below 33°C 4