Keep your body cool to ward off heat stroke

How hot does it have to be outside to get heat stroke, and what exactly causes it?
- Anon.
It's not the temperature outside, but the temperature inside that matters. At a core temperature of about 41C (plus a bit of dehydration) our brains fail and we become confused or pass out. I've seen patients collapse with critical cases of heat stroke in temperatures as mild as 26C. Their natural cooling mechanisms failed and their body's ability to make heat outstripped their ability to shed heat.
Hot weather, strenuous exertion and not drinking enough water are all major factors leading to heat stroke, but the final common pathway is the failure to sweat effectively. We can lose up to 4 litres of fluid an hour by sweating, and evaporation is our body's most effective means of cooling itself.
Once sweating fails because of dehydration, or if high ambient humidity renders evaporation ineffective, core temperature shoots up. Organs start failing, we get confused, our urine output stops and we become unconscious. Rapid cooling and hydration can reverse these insults before they cause coma, multi-organ failure and death.
In the emergency department we do what the body has failed to do: we "sweat" for the patient. We undress them, wet their skin continuously and set fans on them to cause evaporative cooling. This type of external cooling is simple, rapid and effective in most cases.
After cooling has started, we gradually replace the 7-10 litres of fluid that they've lost and tweak their blood sugar and sodium to get it in the normal range. Usually they get better.
But, as with everything else medical, prevention is more effective than cure, so keep these tips in mind when it's hot or humid: seek shade, drink plenty of liquids, avoid alcohol and over-exertion, and seek help if you get so hot you actually stop sweating.
Gary Payinda MD is an emergency medicine consultant in Whangarei.
Have a science, health topic or question you'd like addressed? Email: drpayinda@gmail.com
(This column provides general information and is not a substitute for the medical advice of your personal doctor.)