Heat Illness Summary

Heat Stroke Definition

  • Core temperature ≥ 40.6°C
  • CNS dysfunction (confusion, seizures, coma)
  • Systemic inflammatory response
  • Mortality: 10-50%

Types of Heat Stroke

  • Classic: Elderly, heat waves
  • Exertional: Young athletes, exercise

Emergency Management

  • ABCDE approach first
  • Rapid cooling to <39°C
  • Cooling rate: 0.2-0.35°C/min
  • Monitor core temperature

Cooling Techniques

  • Ice packs (axillae, groin, neck)
  • Evaporative cooling
  • Cold IV fluids
  • Advanced cooling devices

Drug-Induced Hyperthermia

  • Malignant hyperthermia
  • Serotonin syndrome
  • Neuroleptic malignant syndrome
  • Sympathomimetic toxicity

Complications

  • Cardiovascular collapse
  • Renal failure
  • Rhabdomyolysis
  • Coagulopathy
  • ARDS

Other Heat Illnesses

  • Heat cramps: Muscle spasms
  • Heat exhaustion: Systemic symptoms
  • Heat stroke: Medical emergency

Hyperthermia and Heat Stroke

Life-threatening conditions resulting from failure of thermoregulation

Definitions and Physiology

Normal thermoregulation: Body temperature is usually maintained at around 36.5 - 37.5°C, in order to maintain normal enzyme and cell function. Temperature is controlled by the hypothalamus, which monitors body temperature and balances heat production with heat loss.

Hyperthermia

  • Failure of thermoregulation
  • Core temperature exceeds homeostatic mechanisms
  • May be exogenous or endogenous
  • Hypothalamic set point unchanged

Fever vs Hyperthermia

  • Fever: Cytokine-mediated, hypothalamic set point elevated
  • Hyperthermia: Set point unchanged, excessive heat production/insufficient dissipation

Causes of Hyperthermia

Heat Stroke

  • Core temperature ≥ 40.6°C
  • Change in mental state
  • Organ dysfunction
  • Mortality: 10-50%

Types of Heat Stroke

  • Classic non-exertional: Elderly during heat waves
  • Exertional: Young adults during strenuous exercise

Endocrine Causes

Pheochromocytoma

Catecholamine excess causing hypermetabolism

Thyroid Storm

Life-threatening hyperthyroidism

Hypothalamic Dysfunction

Impaired thermoregulatory center

Delirium Tremens

Alcohol withdrawal syndrome

Drug-Induced Hyperthermia

Condition Mechanism Treatment
Malignant Hyperthermia Autosomal dominant disorder of skeletal muscle calcium homeostasis Dantrolene, cooling, supportive care
Serotonin Syndrome Overactivation of serotonin receptors Cyproheptadine, benzodiazepines
Neuroleptic Malignant Syndrome Antipsychotic medication reaction Bromocriptine, dantrolene
Toxidromes Sympathomimetic or anticholinergic Supportive care, specific antidotes

Predisposing Factors for Heat Stroke

Patient Factors

  • Elderly age
  • Obesity
  • Lack of acclimatization
  • Dehydration
  • Cardiovascular disease

Environmental Factors

  • Strenuous exercise
  • High ambient temperature
  • High humidity
  • Poor ventilation

Medical Conditions & Drugs

  • Skin diseases (psoriasis, burns)
  • Endocrine disorders
  • Anticholinergics, sympathomimetics
  • Beta-blockers, calcium channel blockers
  • Alcohol and illicit drugs

Clinical Presentation of Heat Stroke

Diagnostic Criteria: Core temperature ≥ 40.6°C with CNS dysfunction and systemic manifestations.

General Symptoms

  • Extreme fatigue
  • Headache, dizziness
  • Facial flushing
  • Nausea, vomiting, diarrhea
  • Hot, dry skin (sweating in 50% exertional cases)

Cardiovascular

  • Tachycardia
  • Arrhythmias
  • Hypotension
  • High-output cardiac failure

Central Nervous System

  • Confusion, disorientation
  • Seizures
  • Coma
  • Cerebral edema

Systemic Complications

System Complications
Respiratory ARDS, pulmonary edema
Renal Acute kidney injury, rhabdomyolysis
Hepatic Liver failure, elevated transaminases
Hematological DIC, coagulopathy
Metabolic Acidosis, electrolyte disturbances

Emergency Management of Heat Stroke

Primary Goals: ABCDE stabilization and rapid cooling to prevent irreversible organ damage.

Immediate Actions
  1. Transfer to cool environment, lay patient flat
  2. Begin immediate cooling during transfer
  3. Target temperature: <39°C (ideally 38.0-38.5°C)
  4. Achievable cooling rate: 0.2-0.35°C/min
  5. Continuous core temperature monitoring

Cooling Techniques

Simple Methods

  • Cool drinks (if conscious)
  • Fanning undressed patient
  • Tepid water spraying
  • Ice packs (axillae, groin, neck)
  • Watch for shivering response

Advanced Methods

  • Cold water immersion (cooperative patients)
  • Cold IV fluids (4°C normal saline)
  • Intravascular cooling catheters
  • Surface cooling devices
  • Extracorporeal circuits

Important: No specific drugs lower core temperature in heat stroke. Focus on physical cooling methods. If cardiac arrest occurs, continue active cooling during resuscitation.

Other Heat-Related Illnesses

Heat Cramps

  • Clinical features:
    • Heavy sweating during intense exercise
    • Muscle pains or spasms
  • Treatment:
    • Stop physical activity
    • Move to cool place
    • Drink water or electrolyte solutions
    • Wait for cramps to resolve

Heat Exhaustion

  • Clinical features:
    • Heavy sweating
    • Cold, pale, clammy skin
    • Fast, weak pulse
    • Nausea or vomiting
    • Muscle cramps
    • Dizziness, headache, fainting
  • Treatment:
    • Move to cool place
    • Loosen clothing
    • Cool, wet cloths or cool bath
    • Sip water
    • Seek medical attention if vomiting or symptoms worsen

Spectrum of Heat Illness

Condition Core Temperature Key Features Management
Heat Cramps Normal or slightly elevated Muscle spasms only Rest, hydration
Heat Exhaustion 37-40°C Systemic symptoms, no CNS involvement Cooling, medical evaluation
Heat Stroke ≥40.6°C CNS dysfunction, multi-organ failure Emergency cooling, hospitalization