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This is a clinician-written, evidence-based summary aligned to the USMLE Step 2 CK Content Outline. It is intended for medical students preparing for USMLE Step 2 CK. Management reflects current ACC/AHA, USPSTF, and APA guidelines. Always cross-reference with UpToDate, institutional protocols, and clinical judgment.
The Bottom Line
- Use accurate core temperature: rectal, esophageal, bladder, or low-reading thermometer; oral/tympanic can be misleading.
- Hypothermia: mild 32-35 C, moderate 28-32 C, severe <28 C.
- Handle severe hypothermia gently because movement can precipitate VF.
- Heat stroke = core temperature usually >40 C plus CNS dysfunction; rapid cooling is the treatment.
- Exertional heat stroke: ice-water immersion is best when available; goal is rapid cooling before transport when feasible.
Overview
Life-threatening temperature dysregulation requiring accurate core temperature measurement, supportive care, and rapid rewarming or cooling. Emergency management focuses on early recognition, stabilization, targeted investigation, and prompt definitive therapy while avoiding common pitfalls tested on USMLE Step 2 CK.
Epidemiology
This presentation is encountered in emergency and acute care settings. Risk varies by exposure, comorbidity, age, mechanism, and timeliness of treatment. Morbidity and mortality increase when recognition is delayed or when airway, breathing, circulation, antidotal therapy, or definitive source control is postponed.
Clinical Features
Symptoms
Hypothermia: shivering, fatigue, confusion, ataxia, dysarthria, then lethargy and coma
Heat exhaustion: weakness, dizziness, nausea, headache, sweating, tachycardia, but normal mental status
Heat stroke: confusion, delirium, seizure, coma, collapse, or severe agitation
Exertional heat stroke may have profuse sweating; absence of sweating is not required
Drug exposure: stimulants, anticholinergics, salicylates, antipsychotics, serotonergic agents may cause hyperthermia
Signs
Hypothermia: bradycardia, hypotension, slow respirations, cold skin, J waves on ECG
Severe hypothermia: coma, fixed pupils, apparent death, VF/asystole
Heat stroke: core temperature often >40 C with CNS dysfunction
Rhabdomyolysis signs: muscle tenderness, dark urine, hyperkalemia, AKI
Dry hot skin suggests classic heat stroke or anticholinergic toxicity, but is not necessary for diagnosis
Investigations
First-line
Core temperatureRectal temperature for heat illness; low-reading rectal/esophageal/bladder probe for hypothermia.
ECGHypothermia: bradycardia, Osborne J waves, atrial fibrillation, prolonged intervals, VF. Hyperthermia: tachyarrhythmias and electrolyte effects.
Basic labsGlucose, electrolytes, renal function, CK, LFTs, coagulation studies, lactate, blood gas if severe.
Second-line
UrinalysisMyoglobinuria with rhabdomyolysis; monitor urine output.
Toxicology evaluationConsider salicylates, stimulants, anticholinergics, serotonin syndrome, and neuroleptic malignant syndrome.
Infection/trauma workupSepsis, CNS infection, head injury, and endocrine emergencies can mimic temperature-related illness.
Specialist
Extracorporeal rewarming or critical careFor severe hypothermia with cardiac instability/arrest or refractory severe hyperthermia with organ failure.
1
Hypothermia
- Remove wet clothing, insulate, warm environment, warmed blankets, and forced-air warming.
- Mild hypothermia with shivering: passive external rewarming and warm oral fluids if alert.
- Moderate/severe hypothermia: active external warming plus warmed IV fluids and warmed humidified oxygen.
- Severe hypothermia with instability/arrest: consider ECMO/cardiopulmonary bypass rewarming when available.
- Do not pronounce death until adequately rewarmed unless obvious lethal injury exists.
2
Heat exhaustion
- Stop exertion and move to cool environment.
- Oral or IV fluids depending on severity, vomiting, and electrolyte status.
- Evaporative cooling, ice packs, and rest.
- Monitor for progression; CNS dysfunction means heat stroke.
3
Heat stroke
- Immediate rapid cooling — treatment should not wait for labs.
- Exertional heat stroke: cold-water immersion is most effective when feasible.
- Classic heat stroke: evaporative cooling plus ice packs/cooling blankets; rapid cooling remains essential.
- Stop cooling around 38-39 C to avoid overshoot hypothermia.
- Benzodiazepines for severe shivering, agitation, or seizures; avoid antipyretics.
4
Complication management
- Treat rhabdomyolysis with IV fluids and electrolyte monitoring.
- Correct hyperkalemia, hypoglycemia, acidosis, and coagulopathy.
- ICU admission for heat stroke, severe hypothermia, organ dysfunction, persistent altered mental status, arrhythmia, or shock.
Complications
- Hypothermia arrhythmias: Atrial fibrillation, bradycardia, VF, and asystole
- Rhabdomyolysis: Common in exertional heat stroke and prolonged immobilization
- AKI: From rhabdomyolysis, dehydration, shock, or myoglobinuria
- DIC and hepatic injury: Severe heat stroke may cause coagulopathy and acute liver failure
- Neurologic injury: Persistent cognitive, cerebellar, or coma syndromes after severe heat stroke
USMLE Step 2 CK Exam Tips
- 1Heat stroke = hyperthermia plus CNS dysfunction; treat with immediate cooling.
- 2Antipyretics do not work for heat stroke.
- 3Exertional heat stroke can have sweating — do not require dry skin.
- 4Hypothermia ECG with Osborne J waves is classic but not required.
- 5Severe hypothermia can mimic death; continue resuscitation while rewarming.
- 6Handle severe hypothermia gently to avoid precipitating VF.
- 7Heat exhaustion has normal mental status; altered mental status upgrades to heat stroke.
practicetest your knowledge on hypothermia & hyperthermia / heat strokeApply what you've learnt with USMLE Step 2 CK-style questions from the iatroX Q-Bank — emergency medicine and beyond.
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