Exertion Heat-related Illness

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• Results in more than 600 deaths a year in the United States!
• Anticholinergic agents, beta-blockers, and sympathomimetic drugs can all interfere with heat removal and increase risk of heat-related illnesses
• Patients with exertion related heat stroke are commonly young, athletes, or military personnel that present with symptoms after strenuous exercise in the heat

 
Heat Exhaustion

• Occurs via water depletion or sodium depletion or combination
• Water depletion occurs in elderly and persons working in hot environments
• Salt depletion occurs when fluid losses are replaced with hypotonic solutions

 

• Signs & Symptoms
  • Known heat exposure with temperature >37 C with:
    • Tachycardia/Palpitations
    • N/V
    • Diaphoresis
    • HA/malaise/fatigue/generalized weakness
    • Lightheadedness
    • Mentation is normal* (key distinguishing factor from heat stroke)

 

• Evaluation
  • Labs may show:
    • Hemoconcentration
    • Entire spectrum of sodium derangements common electrolyte abnormality

 

• Treatment
  • *NEED to remove from heat-stressed environment
  • Volume and electrolyte replacement as needed
  • Oral fluids vs. IVF 
  • Aggressive cooling (see below)

 
Heat Stroke

• Severe end of heat-related illness spectrum with loss of thermoregulatory mechanisms
• *TRUE EMERGENCY - focus of management should be on immediate, rapid cooling (even if can be started in pre-hospital setting!)
• Mortality = 21-63%; can approach 30% even with treatment
• Hallmark = Elevated temperature >41°C (106°F) + MSOF; heat exhaustion CAN have temperatures >104F
• Occurs when endogenous heat production in combination with absorbed ambient heat exceeds the ability of the body to dissipate heat through adaptive mechanisms (i.e. sweating, hyperventilating, peripheral vasodilation)
• The extent of neurologic injury and mortality is directly related to the peak temperature and duration of the hyperthermia

• Symptoms
  • CNS is particularly susceptible -> AMS, coma, ataxia, confusion, seizures, hallucinations
  • Anhidrosis is frequently present; however, sweating found in up to 50% of patients
  • Shunting of perfusion to less vital organs (e.g. liver, gut) -> GI bleeds, ischemic hepatopathy
  • Compartment syndrome
  • *Hepatic injury is so common (↑AST/ALT) that if not present, consider an alternative diagnosis
• Workup
  • ECG
  • Continuous core temp monitoring 
  • Blood glucose, CBC, CMP (including liver enzymes)
  • VBG (with lactic acid)
  • DIC labs – fibrinogen, D-dimer, PT/INR
  • CK (Rhabdomyolysis – 5x ULN) and UA (myoglobinuria)
  • Chest x-ray
  • CT brain (± LP), if indicated – BE SURE THIS IS NOT MENINGITIS
• Management
  • As always in emergency medicine -> ABCs
  • Remove from environment
  • IVF (for renal protection and avoiding rhabdomyolysis)
    1. Goal UOP 3 mL/kg/hr
    2. Accumulation of intracellular cytoplasmic calcium which leads to myocyte cell membrane damage and ATP depletion -> Hyperphosphatemia and hypocalcemia
    3. Precise guidelines do not exist, but the goal CK should be a level less than 1000 U/L
    4. No target value for creatinine level, however may see ATN
  • Rapid cooling is mainstay of treatment
    1. Reduces morbidity/mortality, needs to be started in prehospital setting
       • Weak evidence available for target temperature; theoretical concern of overshoot hypothermia
    2. No role for antipyretics!
  • Techniques:
    1. ***Cool water immersion
       • Immersion of body to level of torso or neck in cool or ice-water
       • May not be immediately available, so consider other techniques (listed below)
       • As you can imagine, not well-tolerated
       • You will have to take them out of the water in the unfortunate event a patient has a cardiac arrest subsequently
    2. Diffuse application of ice or cold packs to entire body 
       • Benefit may be similar to ice-water immersion
    3. Evaporative/Convective Cooling
       • Set-up large fans and spray tepid water on patient’s body
       • Can perform this while getting ice bath drawn
       • Slightly higher morbidity and mortality compared to immersion
    4. Invasive
       • V V-ECMO, cold water rectal/bladder/NG lavage; bilateral chest tubes with pleural lavage… Weak data, so perform only if needed with caution
• Consider giving antibiotics in addition to IVF hydration as it is difficult to rule out infection as a predisposing factor to the development of heatstrok