From the Guidelines
Hypothermia is categorized into four stages: cold stress, mild hypothermia, moderate hypothermia, and severe hypothermia, with core body temperatures ranging from 35-37°C, 32-35°C, 28-32°C, and below 28°C, respectively. The stages of hypothermia are characterized by distinct signs and symptoms, including shivering, altered level of responsiveness, and decreased level of responsiveness 1.
Stages of Hypothermia
- Cold stress (35-37°C): characterized by alertness and possible shivering, with passive rewarming often being adequate in healthy individuals 1.
- Mild hypothermia (32-35°C): marked by altered level of responsiveness and shivering, requiring protection from harm and passive and active rewarming methods 1.
- Moderate hypothermia (28-32°C): involves decreased level of responsiveness, with or without shivering, and is considered a medical emergency requiring gentle handling, activation of the emergency response system, and all available passive and active rewarming methods 1.
- Severe hypothermia (below 28°C): presents with unresponsiveness, potentially appearing lifeless, and profound hypothermia (below 24°C) is characterized by cessation of shivering, slow heart rate, and breathing, with a high risk for irregular heart rhythm and cardiac arrest 1.
Treatment and Management
Treatment strategies should be tailored to the severity of hypothermia, with mild cases requiring passive rewarming, moderate cases needing active external rewarming, and severe cases necessitating hospitalization with internal rewarming techniques 1.
From the Research
Stages of Hypothermia
The stages of hypothermia are typically classified based on the core body temperature. According to the study 2, the Swiss staging model for hypothermia uses the following temperature ranges:
- Stage 1: <35-32 °C (95-90 °F)
- Stage 2: <32-28 °C (<90-82 °F)
- Stage 3: <28-24 °C (<82-75 °F)
- Stage 4: below 24 °C (75 °F)
Clinical Features and Management
The management of hypothermic patients differs from that of euthermic patients, and advance knowledge about hypothermia is prerequisite to optimal management 3. The evaluation and management of accidental hypothermia involve initial evaluation and stabilization, selection of a rewarming strategy, and criteria for withholding or withdrawing support.
Temperature Ranges and Clinical Stages
The study 2 found that predicting core body temperature using clinical indicators is a difficult task, and there are important overlaps among the four stage groups with respect to core temperature. The lowest observed temperature for each stage was:
- Stage 1: 28.1 °C
- Stage 2: 22 °C
- Stage 3: 19.3 °C
- Stage 4: 13.7 °C
Definition of Hypothermia
Hypothermia is defined as a core body temperature of <35°C 4, 3, 5. Accidental hypothermia occurs when endogenous temperature control mechanisms are incapable of maintaining core body temperature within physiologic limits and core temperature becomes dependent on ambient temperature 5.