Key Facts

Environmental emergencies result from exposure to extreme temperatures, altitude, water, or electrical energy. Core temperature measurement (oesophageal or rectal) is essential for accurate assessment of hypothermia and hyperthermia.

Epidemiology

Hypothermia accounts for approximately 300-500 deaths per year in England and Wales. Heat-related deaths are increasing with climate change. Drowning is a leading cause of accidental death in children. Lightning strikes cause approximately 0-3 deaths per year in the UK.

Aetiology

• Hypothermia: Environmental exposure (outdoor, immersion), urban hypothermia (elderly, homeless, intoxication), iatrogenic (prolonged surgery, massive transfusion)
• Hyperthermia: Heatstroke (exertional — young athletes; classic — elderly in heatwaves), NMS, serotonin syndrome, malignant hyperthermia, drug-induced
• Drowning: Swimming, fall into water, boating accidents, bath (children/epilepsy)
• Altitude: Mountaineering, trekking above 2500m

Pathophysiology

Hypothermia slows metabolic rate, reduces oxygen consumption, and provides neuroprotection. Below 30°C, the myocardium becomes increasingly irritable (risk of VF). Below 28°C, metabolic rate falls to ~50% of normal. Drugs and defibrillation may be ineffective until patient is warmed.

Heatstroke causes direct thermal cellular injury, systemic inflammatory response, DIC, rhabdomyolysis, and multi-organ failure. Core temperature >40°C for >2 hours is associated with high mortality.

Hypothermia

• Mild (32-35°C): Shivering, confusion, ataxia, tachycardia
• Moderate (28-32°C): Shivering ceases, bradycardia, hypotension, reduced consciousness, J waves on ECG
• Severe (<28°C): Coma, VF/asystole, fixed dilated pupils (may be reversible)

Heatstroke

• Core temp >40°C with CNS dysfunction
• Confusion, delirium, seizures, coma
• Hot, dry skin (classic) or sweating (exertional)
• Tachycardia, hypotension, tachypnoea

Drowning

• Hypoxia is the primary insult — aspiration and/or laryngospasm
• Hypothermia may co-exist (neuroprotective)
• Cardiac arrest — primarily from hypoxia

Red Flags

• Core temp <28°C — severe hypothermia; VF risk; warm before pronouncing death
• Core temp >41°C — extreme hyperthermia; active cooling URGENTLY
• Submersion >30 min in warm water — likely poor outcome
• Altered consciousness after diving — consider decompression sickness, AGE

Bedside

• Core temperature: Oesophageal (most accurate) or rectal; tympanic unreliable in hypothermia
• ECG: J (Osborn) waves in hypothermia; arrhythmias
• Blood glucose: Both hypothermia and hyperthermia affect glucose
• ABG: pH, lactate, electrolytes

Bloods

• FBC, U&Es, LFTs, coagulation: Organ function; DIC screening in heatstroke
• CK: Rhabdomyolysis (hypothermia, heatstroke, electrical injury)
• Troponin: Cardiac injury
• Blood cultures: If infection precipitant suspected

Imaging

• CXR: Drowning (pulmonary oedema), hypothermia (aspiration)
• CT head: If altered consciousness not explained by temperature

Special Tests

• Serial core temperature: Monitor rewarming/cooling rate

Hypothermia

• Mild: Passive external rewarming (remove wet clothes, blankets, warm environment)
• Moderate: Active external rewarming (Bair Hugger, warm blankets) + warm IV fluids (40°C)
• Severe: Active internal rewarming (warm IV fluids, warm humidified O2, bladder irrigation, peritoneal lavage); consider ECMO if cardiac arrest
• Cardiac arrest in hypothermia: Continue CPR; withhold adrenaline and defibrillation if <30°C; limit to 3 shocks if <30°C then rewarm to >30°C before repeating

Heatstroke

• Immediate cooling: Remove clothing; ice packs to neck, axillae, groin; cold water immersion if available; evaporative cooling (fan + tepid water spray)
• Target: Core temp <39°C within 30 minutes
• IV fluids: Cool 0.9% NaCl
• Dantrolene 1mg/kg IV: If temperature refractory (also used in MH and NMS)
• Benzodiazepines: For seizures and shivering (shivering generates heat)
• ICU: For multi-organ support (DIC, rhabdomyolysis, AKI, liver failure)

Drowning

• Ventilation and oxygenation: Priority — start rescue breaths in water if safe
• Continue CPR: Especially if cold water — hypothermia may be neuroprotective
• Intubation: If GCS ≤8
• PEEP: For pulmonary oedema (5-10 cmH2O)

Referral Criteria

• Severe hypothermia with cardiac arrest — ECMO centre transfer
• Heatstroke — ICU admission
• Drowning with respiratory failure — ICU
• Decompression sickness — hyperbaric oxygen centre

• Hypothermia: Survival reported after core temp <14°C with ECMO rewarming; 'nobody is dead until warm and dead'
• Heatstroke mortality: ~10-50% depending on cooling time; highest with delayed treatment
• Drowning: Survival depends on submersion time, water temperature, and hypoxia duration; cold water submersion in children has reported survivals after >30 min
• Lightning strike: ~90% survival; cardiac arrest often transient (asystole self-resolves)

Hypothermia Management Summary

Heatstroke vs Heat Exhaustion