Criteria

Clinical staging for accidental hypothermia: the original Swiss system[46]​​[47]

  • Stage 1

    • Estimated core temperature of 90°F to 95°F (32°C to 35°C).

    • Clear consciousness with shivering.

  • Stage 2

    • Estimated core temperature of <90°F to 82°F (<32°C to 28°C).

    • Impaired consciousness without shivering.

  • Stage 3

    • Estimated core temperature of <82°F to 75°F (<28°C to 24°C).

    • Unconsciousness.

    • ECG: ventricular fibrillation or asystole.

  • Stage 4

    • Estimated core temperature classically 75°F to 57°F? (24°C to 13.7°C?).

    • Apparent death; vital signs absent.

    • ECG: asystole.

  • Stage 5*

    • Estimated core temperature of <57°F? or <48°F? (<13.7°C? or <9°C?).

    • Death due to irreversible hypothermia.

*NB: Hypothermia V (HT V) was later removed from subsequent revisions of the Swiss classification system due to uncertain cutoff temperatures based on historic survival records.[47]

Clinical staging for accidental hypothermia: the revised Swiss system[47]

The revised Swiss system uses risk of cardiac arrest in order to stage accidental hypothermia, rather than core temperature.[47]​ It also incorporates the AVPU scale (alert, verbal, pain, unresponsive) to assess a patient’s level of responsiveness instead of using shivering as a stage-defining sign. The revised Swiss system has been designed to simplify clinical staging in the field.

  • Stage 1

    1. "Alert" from AVPU.

    2. Risk of hypothermic cardiac arrest: low.

  • Stage 2

    1. "Verbal" from AVPU.

    2. Risk of hypothermic cardiac arrest: moderate.

  • Stage 3

    1. "Painful" or "Unconscious" from AVPU.

    2. Vital signs present.

    3. Risk of hypothermic cardiac arrest: high.

  • Stage 4

    1. "Unconscious" from AVPU.

    2. No detectable vital signs.

    3. Hypothermic cardiac arrest.

The Wilderness Medical Society: accidental hypothermia classification[48]

  • Mild

    • Estimated core temperature of 95°F to 90°F (35°C to 32°C).

    • Normal mental status, shivering, but not functioning normally and unable to care for self.

  • Moderate

    • Estimated core temperature of 90°F to 82°F (32°C to 28°C).

    • Abnormal mental status with shivering, or abnormal status without shivering, but conscious.

  • Severe/profound

    • Estimate core temperature of <82°F (<28°C).

    • Unconscious.

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