Environmental, Wilderness & Hyper/Hypothermic Emergencies

Resuscitation Quick Ribbon (First 2 Minutes)

Severe Hypothermia:Core temp < 28°C | Active internal rewarming | 'Not dead until warm and dead' (>= 32–35°C)

Heat Stroke:Core temp > 40°C + AMS | Immediate ICE WATER IMMERSION | Goal < 39°C | NO antipyretics!

Frostbite:Rapid warm water rewarming (37–39°C for 15–30 min) | IV tPA within 24h if Grade 3–4

HAPE / HACE:IMMEDIATE DESCENT | HAPE: Nifedipine 30 mg ER + O2 | HACE: Dexamethasone 8 mg IV + O2

Crotalinae (Rattlesnake):CroFab antivenom 4–6 vials IV for advancing swelling or coagulopathy | NO tourniquets!

Bottom-Line Clinical Pearl

In severe hypothermic cardiac arrest (core temp < 30°C), withhold multiple shocks and epinephrine until core temperature reaches >= 30°C, and continue CPR until warmed to >= 32–35°C ('nobody is dead until warm and dead'). For heat stroke (core temp > 40°C with encephalopathy), immediate whole-body cold water immersion provides the fastest cooling rate (~0.2°C/min); antipyretics are completely contraindicated. In rattlesnake envenomation, administer CroFab antivenom immediately for advancing edema or coagulopathy.

1. Accidental Hypothermia & Rewarming Protocols

Hypothermia is defined as a core body temperature < 35°C (95°F). Standard thermometers only read down to 34°C; diagnosis requires a low-reading flexible esophageal (preferred in intubated patients), rectal, or bladder thermistor probe.

Swiss Stage	Core Temp	Clinical Features	Rewarming Strategy
Stage I (Mild)	32–35°C (90–95°F)	Conscious, shivering, tachycardia, cold diuresis	Passive external rewarming: dry clothes, warm blankets, warm sweet oral fluids, warm ambient room (24°C).
Stage II (Moderate)	28–32°C (82–90°F)	Impaired consciousness, shivering ceases, bradycardia, Osborn (J) waves on ECG	Active external rewarming: forced-air warming blanket (Bair Hugger) to TRUNK ONLY (rewarming extremities first causes vasodilation, peripheral pooling, and core temperature afterdrop).
Stage III (Severe)	24–28°C (75–82°F)	Unconscious, profound hypotension, slow AF or junctional rhythm, pulmonary edema	Active internal rewarming: warmed IV crystalloids (40–42°C), humidified heated oxygen (42–46°C), warm thoracic or peritoneal bladder lavage.
Stage IV (Cardiac Arrest)	< 24°C (< 75°F)	No vital signs, ventricular fibrillation or asystole	Veno-Arterial (VA) ECMO or cardiopulmonary bypass is the gold standard rewarming method (warms 6–9°C/hr). Continuous CPR until core temp >= 32–35°C.

Resuscitation Rule — 'Not Dead Until Warm and Dead': If core temp < 30°C: Defibrillate once at max energy; if VF/pVT persists, defer further shocks until core temp > 30°C. Withhold epinephrine and antiarrhythmics until > 30°C (drugs pool in hypothermic circulation without metabolism and cause lethal toxicity on rewarming). Between 30–35°C, double the epinephrine dosing interval to q6–10min. Resuscitation cannot be declared futile until core temp reaches 32–35°C (unless potassium > 10–12 mEq/L or obvious lethal traumatic injury).

2. Heat Illness: Heat Exhaustion vs. Heat Stroke

Heat stroke is defined by hyperthermia (core body temperature > 40°C / 104°F) associated with central nervous system dysfunction (encephalopathy, delirium, ataxia, seizures, or coma).

Feature	Heat Exhaustion	Exertional Heat Stroke (EHS)	Classic (Non-Exertional) Heat Stroke
Core Temperature	< 40°C (usually 37–39°C)	> 40°C (> 104°F)	> 40°C (> 104°F)
CNS Function	NORMAL (alert, mild headache/dizziness)	PROFOUND DYSFUNCTION (ataxia, delirium, coma)	PROFOUND DYSFUNCTION (coma, obtundation)
Sweating	Profuse diaphoresis	Profuse diaphoresis present in 50%	Anhidrosis (dry, hot skin; impaired sweating)
Patient Population	Athletes, laborers in hot environments	Young athletes, military recruits during exertion	Elderly, bedridden, lack of AC, anticholinergics
Management	Rest in cool environment, oral/IV rehydration	IMMEDIATE ICE WATER IMMERSION	Evaporative cooling (mist & fans) + ice packs

Cooling Technique & Goals: Ice water immersion provides the fastest cooling rate (~0.2–0.3°C/min). Submerge the patient up to the neck in iced water while continuously monitoring rectal core temperature. Remove patient when core temperature reaches 38.5–39.0°C to prevent hypothermic overshoot. Administer IV Benzodiazepines (Lorazepam 1–2 mg) to control shivering and seizures. CONTRAINDICATION: Antipyretics (Acetaminophen, Aspirin) are ineffective (hypothalamic set point is normal) and worsen coagulopathy and hepatic failure.

3. Frostbite Staging & Thrombolysis

Direct freezing of tissue with extracellular ice crystal formation, microvascular thrombosis, and reperfusion injury. Rapid active rewarming in a warm water bath (37–39°C / 98.6–102.2°F) for 15–30 minutes until tissue is soft, pliable, and erythema returns is mandatory.

Grade	Depth & Clinical Signs	Blister Characteristics	Tissue Loss / Amputation Risk
Grade 1 (Frostnip)	Superficial epidermal freezing, erythema, numbness	No blisters	No tissue loss
Grade 2	Full-thickness epidermis, edema, erythema	Clear blisters containing prostaglandins	Minimal tissue loss; aspirate clear blisters to remove thromboxane
Grade 3	Full-thickness dermis into subcutaneous tissue	Hemorrhagic blisters (indicates subdermal plexus rupture)	Significant amputation risk; leave hemorrhagic blisters intact to prevent infection
Grade 4	Freezing involves muscle, tendon, and bone	Cold, hard, mummified, black eschar	Complete autoamputation / surgical amputation required

Thrombolysis Protocol for Severe Frostbite: In Grade 3 or 4 frostbite presenting < 24 hours from rewarming, intravenous or intra-arterial catheter-directed Alteplase (tPA) restores microvascular patency and dramatically reduces digital amputation rates. Screen for standard thrombolysis contraindications.

4. High-Altitude Illness: AMS, HAPE & HACE

Disorder	Pathophysiology & Altitude	Clinical Presentation	Definitive Treatment
Acute Mountain Sickness (AMS)	Hypobaric hypoxia leading to cerebral vasodilation (> 2,500 m / 8,000 ft)	Headache + >= 1 of: nausea/vomiting, fatigue, dizziness, insomnia	Rest, halt ascent; Acetazolamide 125–250 mg PO BID (carbonic anhydrase inhibitor induces metabolic acidosis -> stimulates ventilation); Ibuprofen for headache.
High Altitude Pulmonary Edema (HAPE)	Non-cardiogenic pulmonary edema from severe patchy hypoxic pulmonary vasoconstriction (> 3,000 m)	Dyspnea at rest, pink frothy sputum, tachypnea, rales, cyanosis; normal heart size on CXR	IMMEDIATE DESCENT (> 1,000 m); high-flow oxygen; portable hyperbaric chamber (Gamow bag); Nifedipine 30 mg ER PO BID (pulmonary vasodilator) or Sildenafil 50 mg PO TID.
High Altitude Cerebral Edema (HACE)	Vasogenic cerebral edema from capillary leakage and blood-brain barrier disruption (> 3,500 m)	Ataxia (MOST SENSITIVE TEST: tandem gait abnormal), confusion, lethargy, encephalopathy, papilledema	IMMEDIATE DESCENT; Dexamethasone 8 mg PO/IM/IV then 4 mg q6h; high-flow oxygen; hyperbaric bag.

5. North American Pit Viper (Crotalinae) Envenomations

Rattlesnakes, copperheads, and cottonmouths possess complex venom containing hemotoxins, metalloproteinases, and neurotoxins that cause severe local tissue necrosis, thrombocytopenia, and hypofibrinogenemia.

Initial Assessment: Measure and mark the leading edge of swelling with an indelible pen every 15–30 minutes. Order baseline CBC, Platelets, PT/INR, Fibrinogen, and CK.
Indications for Antivenom (CroFab): 1) Progression of local tissue swelling across a major joint; 2) Systemic toxicity (hypotension, vomiting, altered mental status, airway swelling); 3) Coagulopathy (platelets < 100,000/uL, fibrinogen < 100 mg/dL, elevated INR).
CroFab Dosing: Initial dose is 4 to 6 vials reconstituted in 250 mL normal saline infused over 60 minutes. Repeat 4–6 vials if swelling or coagulopathy progresses. Once initial control is achieved, administer 2 vials q6h for 3 maintenance doses.
Strict 'Do Nots': DO NOT place tourniquets or constricting bands (worsens local tissue necrosis); DO NOT make incisions or suck the wound; DO NOT apply ice or electric shock.

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