Heat illness, hypothermia and frostbite: the AU general practice approach

Temperature-extreme emergencies are uncommon in everyday general practice but concentrated around predictable Australian triggers: heatwaves, bushfire seasons, alpine recreation, marathon and sporting events, and occupational heat exposure. Their fatality rate is directly related to speed of recognition and cooling or rewarming. Heat-related death is the leading natural-hazard killer in Australia — greater than deaths from bushfires, floods, cyclones, and storms combined — with the 2009 South-East Australian heatwave killing 374 people from heat alone in Victoria (Doherty Institute). The GP’s prevention role — identifying high-risk patients before heatwaves, reviewing thermoregulation-impairing medications, and educating patients and carers about recognition — is as important as the acute management protocol.

A. Core clinical — the AU general-practice framework

Definitions and spectrum

Hyperthermia spans a spectrum:

• Heat cramps — painful muscle spasms during or after exertion in heat; benign; treat with rest and oral electrolyte replacement.
• Heat exhaustion — core temperature 37–40°C with intact mental state; profuse sweating, weakness, headache, nausea, tachycardia, and orthostasis; reverses with cooling and rehydration without progressing to heatstroke if managed promptly.
• Heatstroke — core temperature >40°C with central nervous system (CNS) dysfunction (delirium, ataxia, seizures, or coma) (Bouchama NEJM 2022). Two clinical phenotypes:
  • Classical (non-exertional) — slow onset over days during a heatwave; elderly, frail, comorbid patients; anhidrosis common at presentation; mortality 10–50%.
  • Exertional — rapid onset during sustained effort in heat; young athletes, military trainees, labourers; sweating often intact; mortality <5% with rapid cooling.

Hypothermia is defined as core temperature below 35°C. The Wilderness Medical Society (WMS) Swiss staging system classifies it clinically:

• HT-I (32–35°C) — alert, shivering, ataxia, “the umbles” (fumbles, mumbles, stumbles, grumbles).
• HT-II (28–32°C) — impaired consciousness, shivering ceases, bradycardia, J-waves (Osborn waves) on ECG, paradoxical undressing.
• HT-III (24–28°C) — unconscious but vital signs present; VF risk rising sharply.
• HT-IV (<24°C) — apparent death, no detectable vital signs; potentially survivable with ECMO rewarming.
• HT-V — confirmed irreversible death.

Cold injury: frostnip (superficial reversible freezing), frostbite (true tissue freezing with ice-crystal formation, classified 1st–4th degree by depth), and non-freezing cold injury (trench foot — prolonged wet cold without freezing).

History

Heat illness: determine the time course of exposure (acute exertional vs days of heatwave at home), hydration status, presence or absence of sweating (profuse in heat exhaustion and exertional heatstroke; absent — anhidrosis — in classical heatstroke), and any mental state change. Medication history is critical: anticholinergics (TCAs, antipsychotics, antihistamines), neuroleptics, diuretics, beta-blockers, lithium, serotonergic agents, and recreational drugs (MDMA/amphetamines, cocaine) all impair thermoregulation.

Hypothermia: establish the type of cold exposure (water immersion = rapid onset; alpine found-down = slower; wet vs dry conditions), duration, alcohol or substance use (peripheral vasodilation accelerates heat loss; impaired judgement including paradoxical undressing is a common presentation), and any underlying condition that predisposes to hypothermia — hypothyroidism, hypoglycaemia, Addison’s disease, or sepsis.

Examination

Core temperature measurement with a rectal or oesophageal probe is mandatory — oral, axillary, and tympanic readings are unreliable in temperature extremes. For hypothermia, a low-reading thermometer capable of recording to at least −20°C is required.

For heatstroke: GCS, orientation, and ability to follow commands — any altered mental state with core temperature >40°C = heatstroke. Note anhidrosis (absent sweating in classical phenotype). ECG (ischaemia, sinus tachycardia). Check urine for brown discolouration (myoglobinuria = rhabdomyolysis).

For hypothermia: cardiac rhythm (bradycardia, AF, J-waves, VF risk), neurological status. Fixed dilated pupils may be present in severe hypothermia without indicating brain death — do not declare death on this finding alone. Assess for frozen tissue.

Investigations

Heat illness: bedside blood glucose (exclude hypoglycaemia as a mimic or coexisting condition), venous or arterial blood gas (metabolic acidosis, lactate), FBC, UEC, LFT (transaminitis universal in heatstroke — AST/ALT often >1,000 U/L), CK (rhabdomyolysis), troponin (cardiac injury), coagulation screen (DIC risk), urinalysis (myoglobinuria), ECG, and blood glucose.

Hypothermia: rectal temperature with low-reading thermometer, ECG (J-waves, AF, QT prolongation), blood gas — potassium >12 mmol/L in pulseless severe hypothermia is a poor prognostic marker for ECMO rewarming candidacy (Brown NEJM 2012), FBC, UEC, glucose, LFT, coagulation, lipase (pancreatitis complication), TFTs and cortisol (myxoedema and Addisonian crisis as aetiological factors), and toxicology.

B. Heat illness — recognition and treatment hierarchy

Heatstroke management

eTG and the WMS Heat Illness guideline 2024 converge on the following:

Exertional heatstroke:

1. Recognise immediately — core temperature >40°C + altered mental state in the setting of exertion.
2. Cold-water immersion (CWI) — the gold standard; immerse to the neck (or torso minimum) in cold water with ice; target core temperature <39°C within 30 minutes: this achieves mortality under 1% (Casa et al. 2015) versus approximately 50% if cooling is delayed beyond 2 hours. Remove from water when temperature reaches 38.5–39°C.
3. Cool first, transport second — where on-site CWI capacity exists and the diagnosis is certain, complete cooling before evacuation; this saves lives.
4. Airway and supplemental oxygen; intubate if GCS <8 or inability to protect airway.
5. IV access with Hartmann’s solution; titrate to MAP and urine output.
6. Treat seizures with benzodiazepines (midazolam 5 mg IV or lorazepam 2–4 mg IV).
7. Avoid antipyretics — the mechanism of heatstroke is environmental and circulatory failure, not cytokine-mediated hypothalamic resetting; paracetamol is ineffective and can worsen hepatic injury; NSAIDs worsen acute kidney injury. Dantrolene has no role (it treats malignant hyperthermia, not heatstroke).
8. Category-1 transfer to ICU — multi-organ failure (rhabdomyolysis, AKI, DIC, ARDS, hepatic failure) is expected.

Classical (non-exertional) heatstroke in elderly patients during a heatwave:

• Move from heat to an air-conditioned environment.
• Evaporative cooling plus ice packs to neck, axillae, and groin — preferred because CWI is logistically challenging and poorly tolerated in frail elderly patients. Method: continuous tepid spray plus electric fan. Target core temperature <39°C within 30 minutes.
• Same airway, fluid, seizure, and transfer management as for exertional heatstroke.
• Identify the triggering circumstance — loss of air conditioning access, social isolation, dementia, thermoregulation-impairing medications.

Differential diagnosis

Several conditions mimic heatstroke and require specific management:

• Neuroleptic malignant syndrome (NMS) — antipsychotic exposure; lead-pipe rigidity; autonomic instability; days-to-weeks course; extremely elevated CK.
• Serotonin syndrome — serotonergic drug exposure; clonus, hyperreflexia, mydriasis; rapid onset.
• Malignant hyperthermia — volatile anaesthetic or suxamethonium exposure; intraoperative; treat with dantrolene.
• Thyroid storm — hyperthyroid history, AF, GI symptoms, suppressed TSH.
• Anticholinergic toxicity — “hot as a hare, dry as a bone, blind as a bat, mad as a hatter” — no sweating, urinary retention, dilated pupils.
• Sepsis — identifiable source; may coexist with heatstroke in vulnerable patients.

C. Hypothermia and cold injury

Hypothermia management

WMS Hypothermia guideline 2024 and Resuscitation Council UK ALS Hypothermia algorithm 2021 guide management:

Mild (HT-I, 32–35°C):

• Remove from cold; remove wet clothing.
• Passive external rewarming — insulating blankets, warm room.
• Warm sweet drinks orally if alert.
• Monitor core temperature until >35°C; hospital transfer if comorbidities present or any concern.

Moderate (HT-II, 28–32°C):

• Active external rewarming — Bair Hugger or forced-air warming blanket.
• Warm humidified oxygen via mask or endotracheal tube.
• Warm IV fluids (Hartmann’s at 40–42°C).
• Continuous cardiac monitoring (VF risk); minimal patient handling — rough movement can trigger VF in a cold heart.
• Ambulance transfer with telemetry to hospital.

Severe (HT-III/IV, <28°C):

1. If pulseless: begin CPR (palpate pulse for at least 60 seconds or use Doppler — the heart rate may be extremely slow).
2. Withhold drugs and limit defibrillation to one attempt until core temperature reaches 30°C — drugs accumulate without effect; defibrillation is rarely successful below 30°C.
3. “No one is dead until warm and dead” — survival with good neurological outcome has been reported after more than 6 hours of CPR plus ECMO rewarming (Walpoth NEJM 1997). Continue resuscitation throughout active rewarming.
4. Active core rewarming — ECMO or cardiopulmonary bypass achieves a rewarming rate of approximately 9°C/hour and is first-choice for HT-IV with cardiac arrest (Brown NEJM 2012). Peritoneal or pleural lavage with warm saline is an alternative if ECMO is unavailable.
5. Potassium >12 mmol/L in pulseless severe hypothermia identifies pre-arrest tissue damage and is a marker of poor ECMO candidacy — this may guide the decision to cease resuscitation.
6. Category-1 transfer to an ECMO-capable centre. Do not declare death until core temperature ≥32°C, unless obvious lethal injury is present.

Frostbite management

Key field principle: do not rewarm if refreezing is possible — a freeze-thaw-refreeze cycle causes more tissue damage than sustained cold.

When definitive rewarming is available:

1. Rapid rewarming in 37–39°C circulating water for 15–30 minutes until tissue is pliable and erythematous; add antibacterial soap.
2. Analgesia — IV opioids; rewarming is intensely painful.
3. Tetanus prophylaxis.
4. Topical aloe vera plus ibuprofen post-rewarming to reduce thromboxane-mediated inflammation.
5. Leave haemorrhagic blisters intact; clear-fluid blisters may be drained.
6. Iloprost or tPA within 24 hours for severe deep frostbite (3rd–4th degree) significantly reduces amputation rates (Bruen Arch Surg 2007) — requires referral to a burns or plastics unit.
7. Delay debridement and amputation 1–3 months until demarcation is clear — “frostbite in January, amputate in July.”
8. Refer to ANZBA pathway for severe frostbite on functional areas (same pathway as deep partial-thickness burns).

D. Australian operations

GP prevention role in heatwaves

The BOM Heatwave Service provides three-day rolling severity forecasts (low/severe/extreme) by region. GPs are embedded in state heat-health plans — Victoria, NSW, South Australia, Queensland, Western Australia, and Tasmania all have coordinated heat-health responses:

• Before each summer: identify housebound elderly and high-risk chronic-disease patients on the practice list; review and consider temporary suspension of thermoregulation-impairing medications (anticholinergics, neuroleptics, diuretics, beta-blockers, lithium) during extreme heat events.
• During a heatwave: check in with isolated elderly patients by phone; advise access to cooled community spaces (libraries, shopping centres). NSW Health Beat the Heat and VIC Department of Health heat health resources are useful patient handouts.
• Advise adequate hydration, thin breathable clothing, and avoidance of mid-day exertion.

Athletes and event organisers: acclimatisation — 10–14 days graded exposure — reduces heat illness incidence by approximately 70%. On-site cold-water immersion capability at marathon, endurance cycling, and football events should be standard. Wet-bulb globe temperature (WBGT) monitoring guides work–rest cycles.

MBS operational items

• MBS 23 (Level B) — in-hours assessment of mild heat illness or post-event review.
• MBS 36/44 (Level C/D) — prolonged consult for chronic-disease patients requiring pre-heatwave medication review and a documented heat action plan.
• MBS 707/715/721/723 — chronic disease management, 75+ health assessment, and care planning: appropriate vehicles for heatwave-vulnerability identification in at-risk patients.
• MBS 597/598 (urgent after-hours) — home-visit assessment of housebound elderly during a severe heatwave, under the sustained-substantial-care criteria.

Notification and reporting

Heat-related deaths are not directly notifiable but warrant coronial referral when death occurs during a heatwave with a likely causal link. Occupational heat illness resulting in serious injury is notifiable to the relevant state SafeWork authority under work-health-and-safety legislation.

E. Special populations

Elderly and frail adults. Classical heatstroke predominantly kills elderly, frail, housebound patients. The combination of impaired thirst sensation, polypharmacy (anticholinergics, diuretics, beta-blockers), and lack of air conditioning is the typical fatal triad. Pre-summer medication review is the highest-yield GP intervention for reducing heatwave mortality in this group.

Pregnant patients. Pregnant women — particularly in the third trimester — have impaired thermoregulation and are at increased risk during heatwaves. Counsel reduced outdoor activity during heat events, prioritise cool environments, and maintain adequate hydration. Reduced foetal movement in the setting of heat warrants same-day assessment.

Infants. Immature thermoregulation and complete dependence on carers make infants highly vulnerable. Never leave infants in closed vehicles. Overheating is also a SIDS risk factor — light clothing, cool rooms, avoiding face covering.

Homeless individuals. At extreme risk during both heatwaves and cold snaps. GPs connected to street health services play a critical role in ensuring access to cooling and warming centres, and in the identification of hypothermia during cold periods.

Athletes and military personnel. Exertional heatstroke predominantly affects this group. Return-to-sport protocols after exertional heatstroke require haematological clearance and graded heat exposure. Counsel coaches and sports medicine staff on “cool first, transport second” and the importance of on-site CWI capability at summer events.

Alpine and wilderness recreationalists. Hypothermia risk is real in Tasmanian and alpine Victorian/NSW environments. Advise filing a trip plan and expected arrival time with parks authorities, wearing layered waterproof clothing, avoiding alcohol before alpine exposure, carrying emergency shelter, and knowing the early signs — “the umbles” in a companion means extracting immediately.

When to escalate

Immediate 000 / category-1 hospital transfer:

• Core temperature >40°C with any altered mental state = heatstroke; do not wait for bloodwork.
• Core temperature <32°C, or any pulseless patient found cold — treat as HT-IV until proven otherwise.
• Suspected NMS or malignant hyperthermia — ICU-level care required.
• Any severe frostbite requiring iloprost or tPA — burns or plastics unit.

Urgent same-day assessment:

• Suspected moderate heat exhaustion not resolving with 30 minutes of oral cooling and rehydration.
• Any elderly patient with new confusion during a heatwave, even without a measured core temperature.
• Found-down patient with hypothermia risk and any comorbidity.

What this article is and is not

This is general health information drawn from Australian and international clinical guidelines — eTG heat-related illness and hypothermia modules, WMS Heat Illness and Hypothermia guidelines 2024, ANZBA, and BOM Heatwave Service — and major published evidence including Bouchama NEJM 2022, Walpoth NEJM 1997, and Brown NEJM 2012. It is not personal medical advice and does not create a doctor–patient relationship. Decisions about acute management are made in real time by the treating clinician with direct access to the patient.

For Australian heat-health consumer resources: NSW Health Beat the Heat, VIC Department of Health heat health, BOM Heatwave Service.

For a life-threatening emergency: call 000 immediately.

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Sources cited

1. Therapeutic Guidelines (eTG) — Heat-related illness
2. Therapeutic Guidelines (eTG) — Hypothermia
3. Australian Bureau of Meteorology — Heatwave Service
4. NSW Health — Beat the Heat
5. VIC Department of Health — Heat Health
6. ANZBA — Australian and New Zealand Burn Association
7. Doherty Institute — heat-related mortality in Australia
8. Wilderness Medical Society — Heat Illness Practice Guideline 2024
9. Wilderness Medical Society — Hypothermia Practice Guideline 2024
10. Resuscitation Council UK — ALS Hypothermia Algorithm 2021
11. Bouchama A. Classical and Exertional Heat Stroke (NEJM 2022)
12. Casa DJ et al. Cold-water immersion for exertional heatstroke (Exerc Sport Sci Rev 2015)
13. Walpoth BH et al. Outcome of survivors of accidental deep hypothermia (NEJM 1997)
14. Brown DJA et al. Accidental hypothermia (NEJM 2012)
15. Bruen KJ et al. Thrombolytic therapy for frostbite injury (Arch Surg 2007)