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Heat Related Illness

It is not uncommon for people to state “I have heat stroke” when they were out in the sun for too long and feel unwell.   Heat stroke is a term that is loosely thrown around, but the fact is – heat stroke is a medical emergency and requires hospital care.  

There are other heat related illnesses besides heat stroke. Understanding what heat related illnesses are and what to do about them is important.  Especially when many areas across Canada are experiencing record-breaking temperatures. 

Why Does Heat Related Illness Happen?

Our bodies are finely tuned to regulate our core body temperatures in a narrow range, averaging around 37°C.  In order to do so, the body must balance heat load (environmental temperatures and internal metabolic processes) with heat loss (sweating and dilation of blood vessels). 

Sweat evaporates off of our skin and is the main way we cool off.  However, sweating becomes ineffective at cooling us down when the environmental humidity is more than 75%.  If the environmental temperature is greater than 35°C, the risk of heat related illness rises.  

As our core body temperature increases and our cooling mechanisms fail, our metabolic demands on our body sharply rise until it reaches a critical point when cell damage starts.  

Children are at a higher risk for heat related illness than adults due to:

  • Higher basal metabolic rate which produces more internal heat
  • Higher body surface area which leads to greater heat absorption from the environment
  • Smaller blood volume so less heat dissipation
  • Less sweating
  • Less likely to drink enough 
  • Less able to acclimatize as quickly

Heat Exhaustion

Heat exhaustion occurs when the body temperature is elevated between 37°C and 40°C.  Other symptoms of heat exhaustion include:

  • Heavy sweating
  • Cold, pale, and clammy skin
  • Fast, weak pulse
  • Nausea or vomiting
  • Muscle cramps
  • Tiredness or weakness
  • Dizziness
  • Headache
  • Fainting

Heat exhaustion can progress to heat stroke unless measures are taken.  Children with symptoms of heat exhaustion should be moved to a cooler place, extra clothing removed, and given cold fluids to slowly sip on.  You can even place cool, wet cloths on their body or have a cool bath.  Contact your doctor if your child is experiencing vomiting, worsening symptoms, or symptoms that do not get better after an hour of taking the previous steps.  

Heat Stroke

Heat stroke is a medical emergency and requires prompt attention.  Heat stroke occurs when the core body temperature exceeds 40°C and there is marked mental status abnormalities (hallucinating, delirious, seizures, slurred speech, coma).  

If you suspect heat stroke, move the person to a cool place immediately with excess clothing removed and place cool cloths on their body and call 911.  Do not try to give them sips of water if there are mental status changes.  

Other signs of heat stroke may include: 

  • Hot, red, dry skin
  • Vomiting
  • Diarrhea

Prevention of Heat Related Illness

Be aware of potential weather forecasts where there may be higher risks of heat related illness.  A heat index of greater than 32°C can pose a risk and more caution should be used.  Physical activities should be adapted to allow for more rest breaks, more hydration, or even rescheduled for a cooler time.  

Children should be strongly encouraged to drink lots of water during hot days, and wear light, loose fitting clothing.  

Have a back-up plan for where you can retreat to for a reprieve from the heat during the day.  

Never leave your child in a car during heat waves.  

This post was co-authored by Erin Manchuk, BScPharm, BCGP and Stephanie Liu, MD, MSc, CCFP, BHSc.

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