Heat Stroke

Introduction

Heat stroke is defined as an elevated core body temperature - typically exceeding 40.5°C - accompanied by central nervous system dysfunction in the setting of a severe environmental heat load that the body cannot dissipate.

  • Body temperature is maintained within a narrow range by balancing heat load with heat dissipation mechanisms (e.g., sweating and cutaneous vasodilation).
  • Temperature elevation is accompanied by an increase in oxygen consumption and metabolic rate, resulting in hyperpnea and tachycardia.
  • In severe cases, patients develop multi-organ failure and disseminated intravascular coagulation (DIC), which can be fatal.

There are two primary classifications of heat stroke:

  • Nonexertional (classic) heat stroke: Occurs due to an inability to escape hot environments. This primarily affects individuals with underlying chronic medical conditions that impair thermoregulation, as well as the elderly and infants.
  • Exertional heat stroke: Occurs in young, otherwise healthy individuals (e.g., athletes, military personnel) who engage in heavy physical exertion during periods of high ambient temperature and humidity.



Management

The successful management of heat stroke requires early diagnosis, immediate removal from the warm environment, and rapid cooling.

Cooling Techniques

  • Cold Water Immersion (CWI): The fastest and most effective cooling method, considered the gold standard for exertional heat stroke.
    • Place the patient in an immersion tub or other suitable container (e.g., a body bag).
    • Fill the container with water and ice. Ice should cover the entire surface of the water.
    • Medical personnel must circulate the water continuously and continually replenish the ice as it melts.
    • Place towels soaked in ice water on the patient's head and neck.
    • Water temperature should be kept below 15°C; the target range is 2-10°C.
  • Tarp-Assisted Cooling with Oscillation (TACO): An effective alternative method for patients with exertional heat stroke when a tub is unavailable.
    • It consists of wrapping the patient in a tarp filled with ice water while oscillating or gently rocking the tarp to increase water movement.
  • Evaporative and Convective Cooling: The preferred method for nonexertional (classic) heat stroke. It involves spraying the naked patient with a continuous cool mist while using large fans to promote evaporation.
  • Alternative Conductive Methods: Additional strategies include ice coverage, strategic placement of ice packs (groin, axillae, neck), and cooling blankets.
Supportive care

  • Airway Management: May require tracheal intubation and mechanical ventilation for patients unable to protect their airway or with deteriorating respiratory function.
  • Fluid Resuscitation: Adequate fluid replacement guided by point-of-care ultrasound, heart rate, blood pressure, and urine output.
  • Hemodynamic Support: Because of pathophysiologic similarities between heat stroke and sepsis, vasoactive agents used to treat septic shock are appropriate for hypotensive heat stroke patients. Norepinephrine (noradrenaline) is a reasonable first-line agent, followed by epinephrine (adrenaline). Dobutamine may be appropriate in select patients requiring inotropic support.
  • Electrolyte Correction: Continuous monitoring and correction of severe electrolyte imbalances. This includes addressing hypernatremia from profound dehydration, hyponatremia secondary to hypotonic fluid intake, and hyperkalemia or hypocalcemia resulting from rhabdomyolysis.


Complications

Regardless of the organ systems initially involved, survivors of heat stroke can experience long-term functional and neurologic impairment.

Acute complications that require immediate management include:

  • Respiratory dysfunction
  • Arrhythmia and cardiac dysfunction
  • Hypotension
    • Managed with IV boluses of isotonic crystalloid (e.g. normal saline 0.9% or Lactated Ringers).
  • Seizures
    • Short-acting benzodiazepines (e.g., IV lorazepam or IM midazolam) should be administered immediately while cooling measures continue.
  • Cerebral edema and neurologic injury
  • Rhabdomyolysis
  • Acute kidney injury
    • Renal replacement therapy (hemodialysis) may be required in severe cases.
  • Hepatic injury
    • Generally self-limited, but in some cases may progress to acute liver failure.
  • Disseminated intravascular coagulation (DIC)
    • Replacement of clotting factors using fresh frozen plasma (FFP) and platelets may be necessary
  • Electrolyte abnormalities



Prevention

Recommended strategies include

  • Maintain hydration by drinking plenty of fluids throughout the day.
  • Opt for lightweight, loose-fitting and light-coloured clothing made of breathable fabrics (e.g. cotton, linen, or hemp) to facilitate evaporation.
  • Avoid or minimize strenuous physical activity during peak heat hours.
  • Utilize a broad-spectrum sunscreen with an SPF of at least 15 and reapply every two hours.
  • Rely on air conditioning during sustained hot weather. Fans may move air around, but air conditioning is the most effective way to lower both ambient temperature and indoor humidity.
  • When traveling to tropical or significantly hotter climates, allow the body 7-14 days to gradually acclimate to the heat before engaging in intense physical exertion.
  • Take cool showers or baths, or rest in air-conditioned spaces immediately after experiencing prolonged heat exposure.



Summary

There is no role for antipyretic agents such as paracetamol or aspirin in the management of heat stroke.

  • The underlying mechanism involves a failure of heat dissipation rather than a change in the hypothalamic set-point.
  • Furthermore, these medications may exacerbate severe complications such as hepatic injury or DIC.
  • Notably, salicylates (like aspirin) can actively contribute to hyperthermia by uncoupling oxidative phosphorylation.

Therefore, once signs of heat stroke are recognized, patients must be immediately directed to the emergency department rather than attempting treatment at home.



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