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Stage hypothermia on the Swiss HT I-IV scale, get the right rewarming steps, wind chill and frostbite times, plus what never to do.
Hypothermia is a core body temperature below 35 °C (95 °F), and the Swiss staging system grades it from HT I to HT IV using signs a rescuer can see without a thermometer: shivering and alert, drowsy with shivering stopped, unconscious with vital signs, and no vital signs at all. This checklist stages the casualty, orders the rewarming actions for that stage, estimates how long each rewarming method needs to get back above 35 °C, and computes the 2001-standard wind chill and frostbite risk for the conditions you are working in.
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The Swiss HT I–IV system was designed for exactly the situation where no core probe exists.
Published rates show why passive shelter at about 1 °C per hour cannot substitute for hospital rewarming.
Conditions are scored with the 2001 wind chill index and its published frostbite exposure times.
Below a core temperature of 35 °C (95 °F). The Swiss stages then run 35–32 °C for mild (HT I, conscious and shivering), 32–28 °C for moderate (HT II, drowsy, shivering has stopped), 28–24 °C for severe (HT III, unconscious with vital signs) and below 24 °C for HT IV, apparent death from cold.
Rubbing pushes cold, acidic blood from the limbs back to a cold and electrically irritable heart, which can trigger a fatal rhythm, and it damages any tissue that is already frozen. Rewarm the trunk — chest, armpits, back — keep the casualty horizontal and handle them gently.
A warm sweet drink helps only someone who is fully alert and still shivering, because it fuels the shivering that is doing the actual rewarming. Anyone drowsy or unconscious must not be given anything by mouth, and a hot bath or shower is dangerous in moderate or severe cases because rapid skin vasodilation can drop blood pressure sharply. Alcohol is never appropriate.
Not necessarily. Pulse and breathing can become extremely slow and hard to detect in severe hypothermia, and people have been resuscitated after prolonged cold cardiac arrest, which is why rescuers check breathing for a full 60 seconds and continue CPR while rewarming. The decision to stop is a clinical one made in hospital, not in the field.