Emergency Medicine: Environmental emergencies

• Temperature: Thermoregulation | Accidental Hypothermia | Cardiac Arrest in Hypothermia | Frostbite and Non-freezing Cold Injury | Heat Exhaustion and Heat Stroke | Other Causes of Hyperthermia
• Water, electricity and gas: Drowning | Electrical Injuries and Lightning | Carbon Monoxide Poisoning
• Bites and stings: Snake Bites — the Adder and Exotic Snakes | Marine Stings and Insect Stings | Tick Bites and Lyme Disease
• Pressure and altitude: Diving Emergencies | Altitude Illness
• Revision: Environmental Emergencies at a Glance | Spot the Diagnosis | Exam-style Scenarios | Key Points | Guidelines and Further Reading

🌡️ Environmental emergencies — heat, cold, drowning, electrical injury, bites and stings, diving and altitude . Environmental emergencies are uncommon but often affect young, previously healthy people (and frail older people in heatwaves and cold snaps), and the correct treatment is very specific: rapid cooling in heat stroke, careful rewarming and prolonged resuscitation in hypothermia, oxygen and recompression for divers, descent at altitude. Getting it right early saves lives and limbs.
Your four questions for every environmental emergency: What was the exposure — and how long? Is there a time-critical intervention (cooling, rewarming, oxygen, antivenom, recompression, descent)? Are there hidden injuries or complications (trauma, rhabdomyolysis, arrhythmia, ARDS)? Who should I call for specialist advice (TOXBASE, NPIS, hyperbaric unit, burns)?

Thermoregulation

• Core temperature is kept at about 37°C (36–37.5°C) by the hypothalamus, balancing heat production (metabolism, muscle activity, shivering) and heat loss.
• Heat loss — radiation (most at rest), evaporation (sweating — main route in heat and exercise; ineffective in high humidity), conduction (cold water — 25 times faster than air), convection (wind).
• Responses to cold — peripheral vasoconstriction, shivering (increases heat production several-fold), behavioural (clothing, shelter).
• Responses to heat — peripheral vasodilatation, sweating (up to 1–2 L an hour in acclimatised people — salt and water loss), reduced activity.
• Who is at risk:
  • Extremes of age — older people (reduced thirst, shivering and sweating; immobility; medications) and infants.
  • Drugs — alcohol, sedatives, antipsychotics, anticholinergics (reduce sweating), diuretics, beta-blockers, sympathomimetics (cocaine, amphetamines, MDMA).
  • Illness — sepsis, hypothyroidism, hypoglycaemia, stroke, spinal cord injury, burns, skin disease, dementia.
  • Social — homelessness, isolation, fuel poverty, outdoor workers, athletes, military.
• Measuring core temperature — tympanic or oral thermometers are unreliable at extremes — use oesophageal (intubated), rectal or bladder probes; low-reading thermometers for hypothermia.

Accidental Hypothermia

• Definition — core temperature under 35°C.
• Causes — environmental exposure (mountains, cold water immersion, homeless people, older people at home after a fall — "long lie"), alcohol and drugs, sepsis, hypothyroidism, hypoglycaemia, stroke, trauma.
• Staging (clinical — Swiss staging, used when core temperature can't be measured):

  Stage	Clinical features	Approximate core temperature	Key risks
  I (mild)	Conscious, shivering, confused	32–35°C	Poor judgement
  II (moderate)	Impaired consciousness, shivering stops	28–32°C	Arrhythmias (AF), bradycardia
  III (severe)	Unconscious, vital signs present	Under 28°C	VF (rough handling), hypotension
  IV	No vital signs	Usually under 24°C	Cardiac arrest

• Features — confusion, slurred speech, ataxia, cold pale skin, bradycardia and hypotension, slow breathing, fixed dilated pupils in severe cases (don't assume death); paradoxical undressing.
• ECG — bradycardia, J (Osborn) waves at the end of the QRS, prolonged PR, QRS and QT, AF, then VF or asystole; shivering artefact.
• Investigations — glucose, U&E (potassium), CK (rhabdomyolysis after long lie), amylase, clotting (cold coagulopathy — lab tests at 37°C may underestimate it), blood gas (correct for temperature per local practice), TFTs, cortisol, toxicology, blood cultures, CT if trauma.
• Rewarming:
  • Handle gently and keep horizontal (rough handling and sudden upright posture can trigger VF and collapse).
  • Remove wet clothes; insulate (blankets, foil, hat).
  • Mild — passive rewarming (blankets, warm room), warm sweet drinks if alert.
  • Moderate and severe — active external rewarming (forced warm air blankets), warmed IV fluids (38–42°C), warmed humidified oxygen; aim for about 1–2°C per hour.
  • Haemodynamically unstable or arrest — active internal rewarming — extracorporeal life support (ECMO or cardiopulmonary bypass), or warm pleural or peritoneal lavage if ECLS isn't available.
• Afterdrop — continued fall in core temperature during rewarming as cold peripheral blood returns.
• Rewarming complications — hypotension (vasodilatation — give fluids), arrhythmias, hyperkalaemia, hypoglycaemia, pulmonary oedema.
• Treat the cause — sepsis, hypoglycaemia, hypothyroidism (myxoedema coma), drugs; older people — falls assessment, social care.

Cardiac Arrest in Hypothermia

• "No one is dead until warm and dead" — hypothermia protects the brain; full neurological recovery has followed prolonged CPR and ECLS rewarming.
• Check for signs of life for up to 1 minute (pulses are hard to feel; use ECG, end-tidal CO₂, ultrasound).
• CPR — standard compression and ventilation rates; mechanical CPR devices for prolonged resuscitation and transport.
• Modified ALS (Resuscitation Council UK / ERC):
  • Under 30°C — give up to 3 shocks for VF or pulseless VT; if unsuccessful, delay further shocks until above 30°C; withhold adrenaline and amiodarone until above 30°C.
  • 30–35°C — shock as normal; give drugs at double the usual interval (e.g. adrenaline every 6–10 minutes).
  • Above 35°C — standard ALS.
• Transfer for ECLS rewarming — patients in hypothermic arrest (or unstable — systolic BP under 90, ventricular arrhythmias, core temperature under 28°C) should go to a centre with extracorporeal rewarming, with CPR continuing during transfer.
• Prognosis — very high potassium (over 12 mmol/L) suggests asphyxia or death before cooling — survival unlikely; the HOPE score estimates survival with ECLS (age, sex, mechanism, CPR duration, potassium, temperature).
• Avalanche victims — burial over 60 minutes with an obstructed airway and asystole has a poor outlook.
• Stopping resuscitation — generally only after rewarming (or when clearly non-survivable injuries, potassium very high, or a frozen chest).

⚠️ Safety Pearl: In hypothermic cardiac arrest under 30°C, give a maximum of 3 shocks and hold adrenaline until the core temperature is above 30°C. Keep going with good CPR and arrange extracorporeal rewarming — decisions to stop are made warm.

Frostbite and Non-freezing Cold Injury

• Frostbite — freezing of tissue (fingers, toes, nose, ears, cheeks) — mountaineers, homeless people, intoxication, Raynaud's, smokers, diabetes.
  • Superficial — white, numb skin that becomes red and blistered (clear blisters) on rewarming — usually recovers.
  • Deep — hard, white or grey-blue, haemorrhagic blisters, no sensation — tissue loss.
• Treatment:
  • Treat hypothermia first; don't rewarm if there's a risk of refreezing (freeze–thaw–refreeze is worse).
  • Rapid rewarming in a water bath at 37–39°C for 15–30 minutes until soft and pink — very painful — give strong analgesia.
  • Don't rub the area or use dry heat; protect blisters (aspirate clear blisters per specialist advice; leave haemorrhagic ones); dressings, elevation, tetanus.
  • Iloprost (IV prostacyclin) or thrombolysis within 24–48 hours for severe frostbite — specialist centres.
  • Delay amputation — demarcation takes weeks ("frostbite in January, amputate in July"); technetium bone scan or MRI helps predict tissue loss.
• Non-freezing cold injury ("trench foot", immersion foot) — prolonged exposure to cold and wet above freezing (military, homeless, festival-goers) — numbness, pain, swelling, hyperaemia, long-term cold sensitivity and neuropathic pain — dry, warm gradually, elevate, analgesia (amitriptyline for neuropathic pain).
• Chilblains (pernio) — itchy, red-purple lesions on toes and fingers after cold exposure — keep warm; nifedipine if severe; consider lupus (chilblain lupus) if persistent.

Heat Exhaustion and Heat Stroke

• Spectrum of heat illness — heat cramps → heat syncope → heat exhaustion → heat stroke.
• Heat exhaustion — core temperature usually under 40°C, normal mental state; fatigue, headache, nausea, dizziness, thirst, sweating, tachycardia — move to a cool place, oral or IV fluids and salt, rest, cooling; recover within hours.
• Heat stroke — a medical emergency (mortality up to 10–50%):
  • Core temperature 40°C or more with CNS dysfunction (confusion, agitation, ataxia, seizures, coma); sweating may be present or absent.
  • Exertional heat stroke — young, fit people exercising in heat (marathon runners, military recruits, festival-goers on stimulants).
  • Classic (non-exertional) heat stroke — older and frail people during heatwaves (often found at home), chronic illness, drugs (anticholinergics, diuretics, antipsychotics).
  • Complications — rhabdomyolysis, AKI, DIC, acute liver failure, ARDS, hypoglycaemia, electrolyte disturbance, multi-organ failure.
• Treatment — "cool first, transport second":
  • Cold water immersion (ice water bath) — the most effective method, especially for exertional heat stroke — cools at about 0.15–0.2°C per minute.
  • If immersion isn't possible — evaporative cooling (spray with water and fan), ice packs to the neck, axillae and groins, cooled IV fluids, cooling blankets; intravascular cooling in ICU.
  • Stop active cooling at about 38.5–39°C (avoid overshoot hypothermia); continuous core temperature monitoring.
  • ABCDE, oxygen, IV fluids (careful — risk of pulmonary oedema in older people), glucose, benzodiazepines for seizures, agitation and shivering.
  • Antipyretics don't work (the hypothalamic set point is normal); dantrolene isn't effective for heat stroke.
  • Monitor CK, U&E, LFTs, clotting, glucose, urine output; ICU if severe.
• Prevention — UKHSA heat-health alerts and heatwave plans (check on vulnerable people, cool rooms, fluids, medication review — diuretics, anticholinergics); acclimatisation and hydration for athletes and the military.

Other Causes of Hyperthermia

• Exertional collapse with hyperthermia at an event — also consider hyponatraemia (overdrinking — exercise-associated hyponatraemia) and cardiac causes.

Drowning

• Drowning — respiratory impairment from submersion or immersion in liquid — a leading cause of accidental death in children and young men in the UK (alcohol, rivers, coastal waters, swimming pools, baths in infants and people with epilepsy).
• Pathophysiology — hypoxia is the key problem — breath-holding, laryngospasm, aspiration → surfactant loss, atelectasis, pulmonary oedema (ARDS) → hypoxic cardiac arrest. Fresh vs salt water makes little clinical difference.
• Cold water immersion — cold shock (gasping, hyperventilation, arrhythmias) in the first minutes, swim failure, then hypothermia.
• Resuscitation (Resuscitation Council UK):
  • Rescue safely; remove from water horizontally if possible.
  • Open the airway and give 5 initial rescue breaths (oxygen as soon as possible) — then 30:2 CPR; compression-only CPR is less effective (hypoxic arrest).
  • Cervical spine immobilisation only if there's a history of diving, water slides, trauma or alcohol with signs of injury (spinal injury is rare).
  • Vomiting is common — suction, recovery position.
  • Prolonged resuscitation in cold water drowning (hypothermia — see above).
• Hospital care — oxygen, CPAP or NIV, intubation and lung-protective ventilation if needed; chest X-ray; ABG; glucose; electrolytes; temperature; look for causes (seizure, arrhythmia — long QT and swimming (LQT1), alcohol, drugs, trauma, non-accidental injury in infants).
• Antibiotics aren't routine (only if contaminated water or signs of infection).
• Discharge — asymptomatic patients with normal observations, oxygen saturation and chest examination after a period of observation (typically 4–8 hours) can be discharged with advice; symptomatic patients are admitted (delayed deterioration).
• Prognosis — depends on submersion time (over 10 minutes poor), time to effective CPR, water temperature, age.

Electrical Injuries and Lightning

• Factors — voltage, current type (AC causes tetanic muscle contraction — "can't let go"; DC throws the victim), pathway (hand-to-hand through the heart is most dangerous), duration, resistance (wet skin lowers resistance).
• Low voltage (under 1,000 V — household mains 230 V AC):
  • Usually minor burns; risk of VF at the time of the shock.
  • Asymptomatic patients with a normal ECG after a domestic shock can usually be discharged.
• High voltage (1,000 V or more — power lines, railways, industrial):
  • Deep tissue damage far greater than skin burns suggest (entry and exit wounds) — rhabdomyolysis, myoglobinuric AKI, compartment syndrome (fasciotomy), fractures and dislocations (muscle contraction, falls), spinal injury.
  • Arrhythmias, myocardial injury; later — cataracts, neurological problems.
  • Burns centre referral; fluids aiming for high urine output; CK; ECG monitoring.
• Lightning (very high voltage, very brief):
  • Cardiac arrest (asystole) and respiratory arrest (brainstem) — the heart may restart before breathing — prolonged ventilation can save lives.
  • Reverse triage at multiple-casualty lightning strikes — treat the apparently dead first (those still conscious are likely to survive).
  • Lichtenberg figures (fern-like skin marks — not burns), keraunoparalysis (temporary limb paralysis with pale, pulseless limbs), tympanic membrane rupture, cataracts, burns from metal objects.
• Scene safety — isolate the power before touching the victim (high voltage — stay at least 18 metres away until isolated).
• ECG monitoring (usually 24 hours) — loss of consciousness, abnormal ECG or arrhythmia, high voltage, significant burns, chest pain, pregnancy (fetal monitoring — fetal death can occur even with minor maternal shocks).
• Tasers — mainly injuries from falls and barbs; ECG if cardiac symptoms; consider drugs and excited delirium.

Carbon Monoxide Poisoning

• Sources — faulty boilers, gas fires and cookers, blocked flues, barbecues and generators indoors, car exhausts, house fires (with cyanide).
• Mechanism — CO binds haemoglobin about 240 times more avidly than oxygen (carboxyhaemoglobin — COHb) and shifts the oxygen dissociation curve left; impairs mitochondrial function.
• Features — headache (commonest), nausea, dizziness, fatigue, confusion — "flu-like" illness — several people (and pets) in the same household affected, better when away from home; severe — syncope, seizures, coma, chest pain and myocardial ischaemia, metabolic acidosis; "cherry red" skin is rare.
• Diagnosis — COHb on a co-oximeter blood gas (venous is fine); pulse oximetry is falsely normal (can't distinguish COHb); smokers may have COHb up to about 10%; levels fall after oxygen, so correlate with time since exposure.
• Treatment:
  • High-flow 100% oxygen via a tight-fitting non-rebreather mask (or intubation) — shortens the CO half-life from about 4–5 hours in air to about 1–1.5 hours.
  • ECG and troponin; treat seizures; consider cyanide toxicity in fires (lactate over 8–10 — hydroxocobalamin).
  • Hyperbaric oxygen — evidence is uncertain — discuss with a hyperbaric centre (e.g. loss of consciousness, neurological signs, pregnancy).
• Complications — delayed neuropsychiatric syndrome (days to weeks — memory, personality, parkinsonism); fetal risk in pregnancy (fetal Hb binds CO more avidly — prolonged oxygen).
• Prevention — CO alarms; gas appliances serviced by a Gas Safe engineer; tell the patient not to return home until the source is identified (inform the gas emergency service).

Snake Bites — the Adder and Exotic Snakes

• The adder (Vipera berus) — the UK's only native venomous snake — zig-zag pattern on its back; bites mostly in summer when people handle or tread on them; deaths are very rare.
• Features:
  • About half of bites are "dry" (no venom).
  • Local — pain, swelling, bruising spreading up the limb, lymphangitis.
  • Systemic envenoming — vomiting, abdominal pain, diarrhoea, hypotension (can be early and recurrent), angioedema, tachycardia, ECG changes, leucocytosis, metabolic acidosis, raised CK, coagulopathy (rare).
• Management:
  • Immobilise the limb (splint) and keep the patient calm; remove rings and watches; no tourniquets, incisions, suction or ice.
  • Mark the edge of swelling with times; observe (admit for at least 24 hours if any signs of envenoming); bloods — FBC, U&E, CK, clotting, glucose; ECG.
  • Antivenom (ViperaTAb) — for systemic envenoming (hypotension, persistent vomiting, ECG changes, leucocytosis, acidosis, raised CK, coagulopathy) or rapidly spreading local swelling (e.g. beyond the wrist or ankle within 4 hours of a hand or foot bite) — discuss with TOXBASE / NPIS; anaphylaxis risk (be prepared).
  • Tetanus; analgesia; antibiotics only if infection.
• Exotic snakes (pets, zoos, travellers) — identify the species; contact NPIS — antivenoms held at specialist centres (e.g. Liverpool, London); some cause neurotoxicity (ptosis, paralysis — elapids) — airway support.
• Scorpion and spider bites — UK spiders rarely cause more than local reactions (false widow — local pain and occasionally infection).

Marine Stings and Insect Stings

• Weever fish (UK beaches — sand shallows) — intense pain after treading on the venomous spines — immerse in hot water (as hot as tolerable — about 40°C — without scalding) for 30–90 minutes (heat-labile venom), analgesia, remove spines, tetanus.
• Jellyfish:
  • UK species — mild to moderate pain and wheals — rinse with seawater (not fresh water — fires remaining stinging cells), remove tentacles with tweezers or a card, hot water immersion for pain, analgesia, antihistamine.
  • Vinegar — for box jellyfish (tropical); may worsen Portuguese man-of-war stings.
• Sea urchin spines — hot water, remove accessible spines, X-ray for retained spines near joints.
• Bee and wasp stings:
  • Local reactions — remove a bee sting quickly by scraping; cold compress, analgesia, antihistamine; large local reactions (over 10 cm) — short oral steroid course if severe; not usually cellulitis (antibiotics rarely needed).
  • Anaphylaxis — IM adrenaline (see Immunology chapter); refer for venom immunotherapy.
  • Multiple stings (swarms) — toxic reactions (rhabdomyolysis, haemolysis, AKI).
  • Stings in the mouth or throat — airway swelling risk.
• Caterpillars (oak processionary moth — urticating hairs — rash, eye irritation, asthma).

Tick Bites and Lyme Disease

• Ticks — common in grassland, woodland and moorland (deer); feed for days; risk of transmission rises the longer they are attached.
• Tick removal — fine-tipped tweezers or a tick-removal tool, grasping close to the skin and pulling steadily upwards without twisting or crushing; clean the site; don't use heat, oils or chemicals.
• No prophylactic antibiotics after a tick bite in the UK (NICE NG95); advise watching for a rash or flu-like illness for 3 months.
• Lyme disease (Borrelia burgdorferi):
  • Erythema migrans — an expanding red rash (often with central clearing — "bull's-eye") at the bite site, usually from 1–4 weeks (range 3–30 days) after the bite — clinical diagnosis — treat without testing.
  • Other features — flu-like illness; later — facial nerve palsy (can be bilateral), meningitis, radiculopathy, carditis (heart block), arthritis (knee), acrodermatitis chronica atrophicans.
  • Treatment (NICE NG95) — doxycycline for 21 days (amoxicillin in pregnancy and children under 9 where doxycycline isn't suitable); IV ceftriaxone for some neurological and cardiac disease.
  • Serology (ELISA then immunoblot) when there's no erythema migrans — may be negative early (repeat at 4–6 weeks).
• Tick-borne encephalitis — rare in the UK (some cases reported) — more common in Europe — vaccine for travellers at risk.
• Prevention — cover skin, insect repellent (DEET), check for ticks after outdoor activity, prompt removal.

Diving Emergencies

• Physics — pressure rises by 1 atmosphere every 10 metres of seawater; gas volume changes inversely with pressure (Boyle's law) and more gas dissolves in tissues at depth (Henry's law).
• Barotrauma — damage from pressure changes in air spaces:
  • Ears (commonest) — ear pain, tympanic rupture, inner ear barotrauma (vertigo, hearing loss — ENT).
  • Sinuses, teeth, mask squeeze.
  • Pulmonary barotrauma — breath-holding during ascent → lung over-expansion → pneumothorax, pneumomediastinum, arterial gas embolism.
• Decompression illness (decompression sickness plus arterial gas embolism) — nitrogen bubbles form on ascent:
  • Decompression sickness — usually within minutes to 24 hours of surfacing — joint pain ("the bends" — shoulders, elbows), skin mottling and itch, neurological (spinal cord — limb weakness, numbness, bladder dysfunction; confusion), "chokes" (cough, chest pain, breathlessness), fatigue.
  • Arterial gas embolism — within minutes of surfacing — stroke-like symptoms, collapse, cardiac arrest.
  • Risk factors — deep or long dives, rapid ascent, missed decompression stops, repeated dives, flying soon after diving, PFO, dehydration, cold, exertion.
• Treatment:
  • 100% oxygen via a non-rebreather mask (washes out nitrogen) — regardless of saturation.
  • Lie flat; IV or oral fluids; treat pneumothorax (chest drain before recompression).
  • Recompression in a hyperbaric chamber — contact the national diving emergency advice line (UK diving doctors) early, even if symptoms improve with oxygen.
  • Transport by road or low-flying aircraft (low cabin altitude); no Entonox (expands gas spaces).
  • Bring the dive computer and dive buddy information.
• Nitrogen narcosis ("rapture of the deep") — at depth; resolves on ascent; oxygen toxicity (seizures) with enriched gas mixes.
• Advice — avoid flying for at least 24 hours after diving (longer after DCI).

Altitude Illness

• Cause — falling barometric pressure at altitude reduces inspired oxygen (at 5,500 m it's about half sea level) → hypoxia; occurs above about 2,500 metres, especially with rapid ascent.
• Acute mountain sickness (AMS) — 6–12 hours after ascent — headache plus anorexia or nausea, fatigue, dizziness, poor sleep (Lake Louise score) — rest, don't ascend further until better, analgesia, antiemetic; descend if no improvement; acetazolamide helps.
• High-altitude cerebral oedema (HACE) — severe AMS progressing to ataxia (heel-to-toe walking), confusion, drowsiness, coma — immediate descent, oxygen, dexamethasone (e.g. 8 mg then 4 mg 6-hourly), portable hyperbaric bag (Gamow bag) if descent impossible.
• High-altitude pulmonary oedema (HAPE) — 2–4 days after ascent — breathlessness on exertion then at rest, cough (frothy, sometimes pink sputum), reduced exercise tolerance, crackles, cyanosis — the commonest cause of altitude death — immediate descent, oxygen, nifedipine (modified release), keep warm, minimal exertion.
• Prevention:
  • Gradual ascent — above 3,000 m, increase sleeping altitude by no more than about 300–500 m a day, with a rest day every 3–4 days; "climb high, sleep low".
  • Acetazolamide (e.g. 125 mg twice daily) — carbonic anhydrase inhibitor (causes a metabolic acidosis that stimulates breathing) — for rapid ascent or previous AMS; side effects — tingling, polyuria, altered taste of fizzy drinks; avoid in sulfonamide allergy.
  • Dexamethasone (AMS/HACE) and nifedipine (previous HAPE) prophylaxis in selected people.
  • Avoid alcohol and sedatives; adequate fluids.
• Patients with heart and lung disease — pre-travel assessment (hypoxic challenge test before flying — commercial aircraft cabins are pressurised to about 1,800–2,400 m).

Environmental Emergencies at a Glance

Spot the Diagnosis