What are the management strategies for hypothermia based on severity grade and body temperature?

Management of Hypothermia by Temperature and Severity Grade

Hypothermia management follows a tiered, temperature-based approach with three severity grades: mild (32-35°C), moderate (28-32°C), and severe (<28°C), each requiring progressively more aggressive rewarming strategies with a target of 36°C and cessation at 37°C. 1, 2

Classification System

The American Heart Association and American College of Critical Care define hypothermia severity as follows: 1, 3

• Cold stress: 35-37°C 1
• Mild hypothermia: 32-35°C 1, 3
• Moderate hypothermia: 28-32°C 1, 3
• Severe hypothermia: <28°C 1, 3
• Profound hypothermia: <24°C 1

Normothermia is defined as 37 ± 0.5°C, and this classification system was adopted universally due to the profound negative physiological impact below 32°C. 3

Temperature Monitoring

Use oral or esophageal probes for accurate core temperature measurement when pulmonary artery catheters are not warranted. 1 Tympanic infrared probes serve as acceptable alternatives when oral measurement is not feasible. 1 Avoid axillary measurements as they consistently read 1.5-1.9°C below actual core temperature, leading to inaccurate treatment decisions. 1 Pulmonary artery catheters, while most accurate, are not recommended routinely due to technical complexity and complications including arrhythmias and perforation. 1, 3

Management Algorithm by Severity

Level 1: Mild Hypothermia (32-35°C)

Implement passive rewarming with environmental control and external insulation. 1, 2

• Remove wet clothing immediately 1, 2
• Move patient to warm environment 1, 2
• Cover with two warm blankets 1, 2
• Shield from wind and insulate from ground 1
• Cover head and neck to minimize heat loss 1
• Provide high-calorie foods or warm drinks if patient is alert 1
• Monitor temperature every 15 minutes 3
• Increase environmental temperature 1, 2

Level 2: Moderate Hypothermia (28-32°C)

Continue all Level 1 measures and add active external rewarming methods. 1, 2

• Apply forced-air warming blankets (e.g., Bair Hugger) which increase rewarming rates to approximately 2.4°C/hour compared to 1.4°C/hour with passive blankets alone 1
• Use heating pads, radiant heaters, or water-circulating warming blankets 1, 2
• Administer warmed intravenous fluids 1, 2
• Provide humidified, warmed oxygen 1, 2
• Monitor temperature every 5 minutes 3, 1
• Implement cardiac monitoring for arrhythmias, particularly bradycardia 1

Critical threshold: Temperatures below 34°C compromise blood coagulation, with each 1°C decrease causing a 10% reduction in coagulation factor function. 2

Level 3: Severe Hypothermia (<28°C)

Continue all Level 1 and Level 2 measures and consider active core rewarming methods. 1, 4

• Activate emergency response system 1
• Handle patient gently to avoid triggering ventricular fibrillation 1, 4
• Consider invasive strategies including: 3
  • Body cavity lavage with warmed fluids 2
  • Extracorporeal life support (ECLS) for cardiac arrest or imminent arrest 5
• Monitor temperature every 5 minutes continuously 4
• Maintain continuous cardiac monitoring 4

Patients with temperature <28°C, ventricular arrhythmia, or systolic blood pressure <90 mmHg should be transferred directly to an ECLS center. 5

Rewarming Targets and Endpoints

Target a minimum core temperature of 36°C before transferring patients between units, and cease rewarming at 37°C. 1, 2, 4 Temperatures above 37°C are associated with poor outcomes and increased mortality. 3, 2 This prevents rebound hyperthermia while ensuring adequate warming before transfer to units where hypothermia management may not be a priority. 3

Monitoring During Rewarming

Monitor continuously for complications including: 1, 4

• Cardiac arrhythmias (bradycardia may be physiologically beneficial) 1
• Coagulopathy 1, 4
• Rewarming shock 1
• Electrolyte abnormalities 1
• Hyperglycemia 1
• Burns from improper use of active external rewarming devices 1

Prehospital Management

Implement Level 1 strategies immediately in all trauma or exposure patients, even without core temperature measurement. 2 Early organized prehospital hypothermia protocols reduce hypothermia incidence from 19% to 3%. 2 First responders should focus on managing life-threatening injuries while simultaneously initiating passive rewarming until hospital arrival. 3

Critical Pitfalls to Avoid

Do not use cold IV fluid boluses for accidental hypothermia (only indicated for therapeutic hypothermia). 1 Do not rely on passive rewarming alone at 33°C or below—active measures are required. 1 Avoid rapid active warming in post-cardiac arrest patients. 2 Hypothermia is frequently overlooked during initial resuscitation; emphasis should be on prevention first, as it becomes increasingly difficult to rewarm patients once significant heat is lost. 2

Special Considerations for Trauma

In trauma patients, heat loss increases to 400 kcal/h (compared to 60-75 kcal/h normally), making even mild hypothermia clinically significant. 3 Warming strategies should continue throughout transfers to CT, operating room, or ICU based on equipment availability and feasibility. 3 Techniques should be used in combination and escalated to more invasive levels if hypothermia is inadequately controlled. 3