Hypothermia
Accidental hypothermia is a core temperature below 35°C: cooling leaves an irritable myocardium that handling alone can tip into arrest, while protecting the brain enough that prolonged resuscitation still works.
Definition
Accidental hypothermia is an unintentional fall in core body temperature below 35°C. It is primary when cold exposure is the cause and secondary when illness, injury or drugs defeat heat production or thermoregulation. Severity is graded by the Swiss staging system on consciousness and vital signs, with a core temperature attached where one can be measured.
First principles
Stage on consciousness when you cannot measure a temperature
The Swiss staging system grades severity on consciousness and vital signs, so it works before any thermometer arrives. Stage one (mild) is conscious and shivering, roughly 35 to 32°C. Stage two (moderate) is impaired consciousness, with shivering reduced or absent, roughly 32 to 28°C. Stage three (severe) is unconscious with a pulse or breathing present, roughly 28 to 24°C. Stage four is apparent death with no vital signs, usually below 24°C, although some patients still have vital signs below that. Those temperatures are estimates, not thresholds, and published versions of the table band them differently. Shivering usually means the core is above 30°C, the band in which hypothermic cardiac arrest is unlikely.
This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.