Heat-related illnesses

Feature	Heat Cramps	Heat Exhaustion	Heat Stroke
Core Problem	Electrolyte loss	Water & salt loss	Thermoregulatory failure
Core Temp	Normal	< 40°C (104°F)	> 40°C (104°F)
CNS Status	Normal / Alert	Intact (dizzy, headache)	Altered (confusion, seizure, coma)
Skin	Moist	Cool, pale, moist	Hot, dry OR moist
Tx Priority	Electrolyte fluids	Cool down, fluids	Immediate rapid cooling (e.g., ice bath)

1. Heat Cramps

• Pathophysiology/Etiology: Painful, involuntary muscle spasms during or after strenuous activity in the heat. Believed to be caused by electrolyte imbalances (e.g., hyponatremia) from heavy sweating and replacement with hypotonic fluids.
• Clinical Presentation: Affects heavily used muscles (calves, thighs, abdomen). Core body temperature is normal. Patient is alert.
• Management: Rest in a cool environment, gentle stretching of the affected muscle. Oral rehydration with electrolyte-containing fluids (e.g., sports drinks) is preferred. IV normal saline may be needed if oral intake is not possible.

2. Heat Exhaustion

• Pathophysiology/Etiology: The body’s response to an excessive loss of water and salt, usually from profuse sweating. It’s a milder form of heat illness that can progress to heat stroke if untreated.
• Clinical Presentation: Characterized by non-specific symptoms like headache, nausea, vomiting, dizziness, weakness, and heavy sweating. Core body temperature is typically elevated but &lt 40°C (104°F). Crucially, there is no significant CNS dysfunction (e.g., seizures, coma). The skin is often pale and moist.
• Management: Move patient to a cool environment. Aggressive fluid and electrolyte replacement, orally if possible, or with IV fluids if symptoms are severe or there is vomiting.

3. Heat Stroke

• Pathophysiology/Etiology: A medical emergency caused by the failure of the thermoregulatory system, leading to uncontrolled elevation of core body temperature. This hyperthermia causes a systemic inflammatory response, protein denaturation, and can lead to multi-organ failure.
  • Classic (Non-exertional): Affects sedentary individuals, often elderly or with chronic illnesses, during heat waves.
  • Exertional: Occurs in healthy, young individuals during strenuous physical activity in hot/humid conditions.
• Clinical Presentation: The hallmark is a core body temperature > 40°C (104°F) accompanied by CNS dysfunction (e.g., delirium, confusion, seizures, coma). Skin may be hot and dry (classic) or diaphoretic (exertional). Tachycardia and tachypnea are common.
• Diagnosis: Primarily a clinical diagnosis based on rectal temperature and CNS status. Labs may show rhabdomyolysis (↑ CPK, hyperkalemia), transaminitis (elevated AST/ALT), and electrolyte disturbances.
• DDx: Sepsis, meningitis, encephalitis, neuroleptic malignant syndrome, serotonin syndrome, and toxic ingestions (e.g., cocaine, amphetamines).
• Management: This is a true emergency focused on immediate and rapid cooling.
  • ABCs: Ensure airway, breathing, and circulation.
  • Rapid Cooling: The cornerstone of treatment is lowering the core body temperature to ~39°C (102°F) as quickly as possible.
    • Evaporative cooling (spraying with lukewarm water and fanning) is widely used.
    • Ice-water immersion is highly effective, especially for exertional heat stroke.
    • Apply ice packs to axillae, groin, and neck.
  • Supportive Care: IV fluid rehydration and management of complications like seizures (with benzodiazepines), rhabdomyolysis, and organ failure in an ICU setting. Antipyretics (e.g., acetaminophen) are not effective as the pathophysiology is not a change in the hypothalamic set-point.