Hypothermia is a drop in core body temperature below 35°C. In the mountains it develops insidiously — it starts with shivering and fatigue, and by the time it enters the moderate stage the victim stops cooperating and often does not realize they are in mortal danger. This article shows how to recognize the early signs, why the Swiss Staging classification is key to treatment decisions, and which field mistakes to avoid.
In a nutshell — hypothermia stages and symptoms
- HT I (35–32°C, mild) — shivering, agitation, tachycardia, blue lips
- HT II (32–28°C, moderate) — shivering ceases, impaired consciousness, bradycardia
- HT III (28–24°C, severe) — unconscious, basic life functions preserved
- HT IV (<24°C, extreme) — “apparent death”, cardiac arrest
- Axillary or tympanic temperature measurement in the field is unreliable — clinical judgment rules
Swiss Staging — why this classification
ICAR MEDCOM (International Commission for Alpine Rescue, Medical Commission) recommends the Swiss clinical staging instead of relying on temperature measurement alone. Practical reason: thermometers reaching core temperature (esophageal, rectal, bladder) are unavailable in the field, and axillary or tympanic measurements can differ from true core temperature by as much as 3–5°C.
Swiss Staging is based on clinically observable features: presence or absence of shivering, level of consciousness, cardiovascular and respiratory function. It is a model built by alpine physicians for alpine physicians and rescuers — not for hospital intensive care.
HT I — mild hypothermia (35–32°C)
Clinical signs
- Intense shivering — body tries to generate heat via muscle tremor
- Elevated heart rate and respiratory rate
- Peripheral vasoconstriction — pale, cold hands and feet
- Blue lips, sometimes fingers
- Agitation and increased activity (body is “fighting”)
- Coordination impairment — difficulty zipping a jacket, opening a backpack
- Minimal or no cognitive impairment
Field questions that help confirm diagnosis
- “Get a match out of your pocket” — fine finger motor control is significantly impaired already in HT I
- “What day is today? What’s your name? Where are we?” — orientation preserved but answers slower
- “Walk along this line” — motor coordination impaired
HT II — moderate hypothermia (32–28°C)
- Shivering stops — this is a clinical watershed, a sign that the body can no longer compensate
- Psychomotor slowing, drowsiness, apathy
- Confusion, disorientation
- Paradoxical undressing — victim feels a heat surge and removes clothing (peripheral vasoconstriction fails, blood rushes to skin)
- Muscle rigidity, gait disturbance
- Bradycardia, shallow breathing
- Disorientation to time and place
Paradoxical undressing is a classic, dangerous sign — the victim removes a hat, unzips a jacket, in extreme cases trousers. A half-naked body found in snow can lead to a misread of assault at autopsy. Knowledge of this mechanism allows rescuers to correctly interpret the scene.
Why stopping shivering is so important
Shivering is the body’s largest natural “heat generator” — it can increase heat production by 500% over resting metabolism. When the victim stops trembling despite low ambient temperature, it means muscle glycogen has been depleted and compensatory mechanisms are failing. From this moment on the body slides into hypothermia without its own brake.
HT III — severe hypothermia (28–24°C)
- Unconscious, but basic life functions preserved
- Pulse slow and hard to feel — sometimes only at carotid
- Shallow, slow breathing (3–5/min), may appear absent
- Pupils dilated, light response weakened or absent
- Muscle rigidity, no reflexes
- High risk of ventricular fibrillation from any stimulation
At this stage every movement of the victim must be minimal and precise — sudden handling or chest compressions can trigger VF in the cold myocardium. If the patient is breathing with pulse — do not perform chest compressions. Exception: documented cardiac arrest.
HT IV — extreme hypothermia (<24°C)
- Cardiac arrest (VF or asystole) or “apparent death” state
- No response to stimuli
- No palpable pulse or breathing
- Pupils widely dilated, no light response
- Whole-body rigidity
Cardinal rule of deep hypothermia: nobody is dead until warm and dead. Metabolism is so slowed that the brain can survive up to an hour without circulation. Literature describes full neurological recovery after CPR lasting >6 hours — with ECMO rewarming in intensive care.
Common diagnostic mistakes
- Axillary temperature in HT II+ — vasoconstriction distorts measurement; axillary reading can be several degrees higher than core
- Trusting “I feel fine” in HT II — confusion masks self-assessment; patients routinely insist they are “just a bit cold”
- Mistaking shivering for “emotional shaking” — in an avalanche victim post-extraction, shivering is often attributed to stress while HT I is already setting in
- Underestimating exposure time — at 0°C with 5 m/s wind, 30 min of sitting in wet clothing suffices to develop HT I
- Assumption “if they can talk, they’re fine” — speech is preserved into HT III; a patient may still converse at core 28°C
When to call for help
Practical rule: any suspicion of HT II or deeper — call for help immediately, before starting medical interventions. Helicopter evacuation from HT III/IV requires coordination with an ECMO-capable hospital (extracorporeal circulation). This information must reach the dispatcher at the moment of the call, not after the team arrives.
Emergency numbers in Poland:
- 112 — European emergency number
- TOPR: 601 100 300 — Tatra mountains
- GOPR: 985 — other Polish mountain ranges
More on step-by-step management — Hypothermia in the mountains — full guide and Hypothermia wrap — building field insulation.
Frequently asked questions
Why do hypothermic people undress themselves?
This phenomenon is called paradoxical undressing and occurs in moderate hypothermia (HT II, 32–28°C). Severe thermoregulation disruption causes the brain to receive false overheating signals — the victim feels a heat surge and instinctively removes clothing. Neurologically: peripheral vasoconstriction fails, blood rushes to the skin, creating illusory warmth. It is a sign of advanced hypothermia requiring immediate evacuation.
When does shivering stop and is that a good sign?
Shivering typically stops at core temperature 32°C (HT I → HT II transition). This is NOT a good sign — it indicates muscle glycogen depletion and compensatory failure. From that moment the body cannot produce its own heat and cannot recover spontaneously. Immediate insulation, escort to warmer location, and hospital evacuation are mandatory.
Can axillary temperature assess hypothermia?
In the field — no. Peripheral vasoconstriction in hypothermia distorts axillary and tympanic measurements by 1–5°C. Accurate core temperature requires esophageal, rectal, or bladder thermometers — hospital equipment. Mountain medicine practice uses Swiss Staging based on observable signs: shivering, consciousness, cardiorespiratory function.
How fast does hypothermia develop?
Depends on conditions. In wet clothing at 0°C with 5 m/s wind, first HT I signs may appear in 30–60 min. In 5°C water (falling into a cold stream, river crossing), HT II may develop in 15–30 min. Extremely fast cooling occurs with avalanche burial — rate ~3°C/h, HT II reached in about 60 min.
Can hypothermia be distinguished from hypoglycemia in the field?
It can be tricky — both cause confusion, weakness, tremor, cold sweats. Key differences: hypoglycemia gives tachycardia, warm dry skin, responds to carbohydrates in 10–15 min. Hypothermia gives bradycardia in moderate stage, cool skin, no food response. If in doubt on expedition: give carbohydrates (banana, energy gel) — if hypoglycemia, symptoms resolve; if hypothermia, no harm done and you start thermal insulation regardless.
References
- Brown DJ, Brugger H, Boyd J, Paal P. Accidental hypothermia. N Engl J Med. 2012;367(20):1930–1938.
- Paal P, Pasquier M, Darocha T, et al. Accidental hypothermia: 2021 update. Int J Environ Res Public Health. 2022;19(1):501.
- Auerbach PS, Cushing TA, Harris NS (eds). Auerbach’s Wilderness Medicine, 7th ed. Elsevier, 2016.
- ICAR MEDCOM guidelines — alpine-rescue.org.
Disclaimer: This article is for informational purposes only and does not replace individual medical consultation. In life-threatening situations call local mountain rescue (Poland: 112, TOPR 601 100 300, GOPR 985).