Heat Related Emergencies

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Heat Related Emergencies

• Mike McDonnell, MD

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Scenario

• HUSAR team gets deployed to the collapse of an
  office tower in downtown Toronto
• people are trapped
• mid August, 30ºC with Humidex feels like 40ºC
• team member complains of cramps, stops working
  and drinks, goes back to work
• later found sitting in corner, staring, mumbling
  about mummy

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Objectives

• physiology of heat transfer/cooling
• heat related illnesses
• types
• Treatment
• on the pile vs. in the pile

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Physiology of Heat Transfer

• Supply and Demand relationship
• Supply (heat production)
• BMR
• without cooling, temperature increases 1.1ºC/hr
• Increases up to 20X with strenuous exercise

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Supply and Demand

• Demand (heat loss)
• Conduction
• warm body to cooler surroundings (2)
• Convection
• heat loss to air and water
• better with loose clothing, higher wind velocity
• Radiation
• electromagnetic waves
• great in cool temperatures, net gain when warm
• Evaporation
• conversion of liquid to gas
• major factor non-acclimatized sweat 1
  litre/hour
• not effective when relative humidity gt75

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Physiology of cooling
We are like a water cooled car....
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Heat Related Illnesses

• Spectrum
• Not so bad, bad, very bad

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Not so bad

• Prickly Heat
• obstruction of the sweat gland pores, produces
  vesicles, sometimes ruptures, very itchy
• can get superinfected/rupture
• treated with chlorhexidine, antibiotic creams,
  loose clothing preventative

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Not so bad

• Heat edema
• nonacclimatized individuals
• standing for long periods of time
• affects feet and ankles
• treated with leg elevation

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Not so bad

• Heat Cramps
• brief, intermittent, severe cramps in working
  muscles
• early on in work in hot environment
• heavy sweaters with hypotonic fluid replacement
  more at risk
• usually after exertion
• treatment
• Rapid elevation of salt solutions ½ tsp salt in
  quart of water, commercially available solutions
  taste better

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Bad

• Heat Syncope
• vasodilation and venous pooling from standing
• reduced circulating blood volume
• volume loss makes it worse
• elderly are more susceptible
• treatment fix causes/injuries

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Bad

• Heat Exhaustion
• volume depletion under heat stress
• two types water and salt depletion
• water inadequate fluid replacement
• salt hypotonic fluid replacement

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Heat Exhaustion

• Signs and Symptoms
• vague malaise, fatigue, headache   
• core temperature often normal if elevated, less
  than 40 C (104 F)   
• mental function essentially intact no coma or
  seizures   
• tachycardia, orthostatic hypotension, clinical
  dehydration (may occur)   
• other major illness ruled out   
• if in doubt, treat as heat stroke

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Heat Exhaustion - Treatment

• rest   
• cool environment   
• assess volume status   
• fluid replacement normal saline to replete
  volume if patient orthostatic, replace free water
  deficits slowly to avoid cerebral edema

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Very Bad

• Heat Stroke
• Hallmark alteration in level of consciousness
• thermoregulation is overwhelmed and fails
• may be a prodrome, may be like heat exhaustion
• rapid treatment is essential

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Heat Stroke

• Diagnosis
• exposure to heat stress
• signs of severe CNS dysfunction (coma, seizures,
  delirium)   
• core temperature usually above 40.5 C (105 F),
  but may be lower   
• dry, hot skin common, but sweating may persist   

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Types

• Classic and exertional

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Treatment

• cooling immediately is key to survival
• use all methods of heat transfer
• spraying atomized cool water (evaporation)
  combined with fans (convection) very effective
• ice water immersion can be attempted
• rapid but take out when body temp lt 39ºC
• ice packs/cooling blankets less effective

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Complications

• aspiration and seizures are common
• airway control
• tachyarrhythmias are common
• usually resolve with cooling
• dont over hydrate (IV fluids) pulmonary edema
• agitation benzodiazepines
• shivering chlorpromazine, Demerol?