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Heatstroke and Heat Exhaustion

Heat Exhaustion

Your only chance to do Slickrock came in July. You tried to get an early start, but you're just not a "morning person." Halfway around the loop, you're sweating buckets. You have a headache. Now you're feeling nausea. Your muscles are feeling weak, even the arms. You start walking the bike because you're feeling, well, like crap.

"Heat exhaustion" means your body is starting to malfunction due to "heat stress" -- dehydration, electrolyte depletion, and overheated muscles. At this stage, you can reverse these changes, but it may take a little time. Complete recovery from dehydration can take hours.

It's a short hop from heat exhaustion to heat stroke, which can kill you or leave you with brain damage.

Immediate care:
Get out of the sun immediately. Remove extra clothing. Spread arms and legs to increase evaporative surface. Sit or lie down to reduce muscle effort -- while keeping as much skin open to the air as possible. If there is cool water nearby, use it to wipe down the body. Sip whatever liquids you have with you, ideally a low-sugar electrolyte drink like Gatoraid. Once you think you've recovered, mosey back to civilization and continue rehydration for a couple of hours. If the dehydration is severe, use a balanced electrolyte solution such as Lytren or Pedialyte

Dehydration and Electrolyte Abnormality

Dehydration means loss of circulating water volume. When biking, you lose water through sweat, through the lungs by rapid breathing, and through the kidneys. (If you take diuretics -- water pills -- the inability of the kidneys to "hold on" to water can become a problem during prolonged exercise.) The higher metabolism means you lose water much more rapidly than at rest. You may lose a lot of water and sodium through sweat even if you don't feel damp.

There are three problems that occur with exercise-induced dehydration: acidosis, hypokalemia, and sodium/water imbalance. All of these things are better AVOIDED, rather than treated, by attention to adequate hydration and (if sweating and exercise are prolonged) electrolyte replacement while biking.

Acidosis: Don't try to treat acid buildup (acidosis). Just get plenty of fluids, and let your kidneys sort things out.

Hypokalemia: Potassium losses (hypokalemia) become apparent after the acidosis is corrected. If severe, it can cause weakness, muscle cramps, and heart rhythm disturbances (such as premature beats). Your body will move potassium out of the cells to partially correct the loss. It may take hours to correct. You'll get potassium from yogurt, bananas, and (a tiny bit) from sport drinks. If you're taking some types of blood pressure medicines or diuretics (water pills) potassium loss can be a problem.

Sodium/water Imbalance: Your body needs a certain ratio of sodium to water in your blood. As you sweat heavily, you lose both salt and water. If you don't take water by mouth, the water loss exceeds the sodium loss and the serum becomes extra salty. This is called hypernatremia. Weakness, muddled thinking, and lightheadedness occur with this type of dehydration. It's fixed by drinking water. If sweat volume is high, and being replaced by pure water, the body begins to run out of salt. The blood becomes dilute with low sodium, called hyponatremia. Symptoms include weakness, irritability, and (if severe enough) risk of seizures. The best prevention is to replace sodium along with water during prolonged heavy sweating by using electrolyte-solution sport drinks. For treatment of dehydration with hyponatremia, the sport drinks are still too dilute in electrolytes. It's best to grab several jugs of kiddie-diarrhea electrolyte-replacement solution, such as Lytren or Pedialyte.

See the doctor if:
    - you're profoundly weak
    - your heart is racing or irregular
    - you have shortness of breath, chest pain, or severe lightheadedness
    - nausea prevents oral rehydration


You're sweating like a pig in the St. George sunshine, trying to figure out the Stucki Springs trail. Dang that CamelBak is heavy on the uphills! So you dump out some water. Getting kind of dizzy. Don't stop, because the wife will be waiting. Odd -- you're getting goosebumps despite the heat, but at least you're not sweating so much any more. Which fork do you take here? Sure is hard to figure out this old map. Boy, this heat is making you dizzy. Better sit down for a minute. Whoops, kind of fell down there.

Heatstroke occurs when your heat-regulation system fails. Often sweating stops and there are signs of excess adrenaline such as goosebumps. The body temperature climbs and begins to interfere with thinking. Symptoms of heat exhaustion usually precede the confusion that marks the beginning of heatstroke. Finally, consciousness is lost and brain damage (and death) can occur rapidly.

When has a biker passed the line between heat exhaustion and heat stroke? To oversimplify: if the brain isn't working perfectly (confusion, dizziness even when lying down, etc) you've crossed the line from dangerous to deadly.

Immediate care:
Immediate cooling can be lifesaving. (Often, the victim can no longer sweat, so the temperature just keeps rising. You can't just "wait it out.") Get the person out of the sun immediately. Remove extra clothing. Spread arms and legs to increase evaporative surface. Have them lie down, while keeping as much skin open to the air as possible. Wet your biking shirt, then drag it loosely over exposed skin, moving from one area to another. Keep the cloth loose and very wet, letting it pass through the air to cool between wipes. If there's a cool but shallow stream nearby, consider moving the victim so their back and legs are in the water. If you're close to a camper where ice is available, put ice in the groin, armpit, and under the back. If the victim remains confused or becomes unconscious, send someone out for help -- a helicopter or ambulance.

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