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Core temp < 28°C | Active internal rewarming | 'Not dead until warm and dead' (>= 32–35°C)
Core temp > 40°C + AMS | Immediate ICE WATER IMMERSION | Goal < 39°C | NO antipyretics!
Rapid warm water rewarming (37–39°C for 15–30 min) | IV tPA within 24h if Grade 3–4
IMMEDIATE DESCENT | HAPE: Nifedipine 30 mg ER + O2 | HACE: Dexamethasone 8 mg IV + O2
CroFab antivenom 4–6 vials IV for advancing swelling or coagulopathy | NO tourniquets!
Chilblains = inflammatory skin lesions from cold damp exposure above freezing; Trench Foot = non-freezing immersion foot injury from prolonged wet boots. Treat with warm water soaks and nifedipine.
Intravenous prostacyclin analog (Iloprost) administered within 48 hours of severe grade 3-4 frostbite dramatically reduces digit amputation rates.
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.
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. |
Critical Pitfall / Contraindication
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).
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 |
Critical Pitfall / Contraindication
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.
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 |
Critical Pitfall / Contraindication
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.
| 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. |
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.
Test Your Environmental, Wilderness & Hyper/Hypothermic Emergencies Clinical Acumen
Directly launch an active-recall practice block from our validated question bank with comprehensive explanations and distractor analyses.
Distinguish primary life-threats from mimics. On board exams (COMLEX Level 1, 2-CE, 3 & USMLE), initial stabilizing interventions (airway, IV access, non-invasive ventilation, empiric reversal) always take precedence over diagnostic imaging.
Evaluate autonomic tone: Sympathetic viscerosomatics (T1–L2) cause acute paraspinal tissue texture changes (erythema, bogginess, hypertonicity). Suboccipital release (CN X Vagus) and rib raising normalize autonomic outflow and thoracic cage mechanics.