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Heat-related illness can quickly and frighteningly derail an otherwise spectacular outdoor adventure. Dehydration, heat exhaustion, heat stroke, and hyponatremia afflict even seasoned outdoorspeople, but with some diligence, these illnesses are preventable. Heat-related illnesses can also be sneaky. They don’t require a desert hike in July to strike; a sunny, 75-degree winter day can be sufficiently hot to cause problems for someone who lives where the average temperature is 35 degrees.
Heat-related illnesses fall on a spectrum ranging from mild to life-threatening. It’s critical to understand how to prevent these issues, which is a topic covered in detail in a subsequent section. It’s also important to be able to distinguish between different heat-related issues and know how to treat each one, bearing in mind that the goal is to prevent a smaller problem from progressing into more serious conditions.
What it is: Dehydration is an inadequate intake of water that results in inadequate volume of water in the body.
Signs and Symptoms: Mild signs and symptoms include thirst and dry lips. As severity increases, signs and symptoms can include headache, fatigue, irritability, and increasingly darker-colored urine. A severely dehydrated person can experience an altered level of consciousness and hypovolemic shock, a serious medical condition resulting from inadequate blood volume.
Treatment: Drink water! To quench the initial thirst of dehydration, most people want to chug a large amount of water. But after that initial swig, focus on drinking smaller amounts of water at regular intervals, and be sure to snack, too. The goal is quenched thirst (see section below regarding thirst) and very light colored urine. A great guideline for exercising in hot conditions is to consume about .25 liters of water every 15-20 minutes. Drinking large amounts of water without ingesting food, specifically salty food, can lead to a dangerous condition known as hyponatremia, described below.
What it is: Heat exhaustion is a problem resulting from heat stress, water and electrolyte loss, and ineffective hydration. It is fundamentally a problem of dehydration, as opposed to the far more serious heat stroke described below.
Signs and Symptoms: This condition is characterized by increased heart rate and respiratory rate, flushed and sweaty skin, headache, fatigue, and nausea. Sometimes, a person suffering from heat exhaustion is so sweaty they actually experience chills or have goosebumps.
Treatment: A person suffering from heat exhaustion needs to be aggressively cooled. Move them into shade. The most effective way to cool someone down is by getting them wet and fanning them. While continuing to cool the patient, encourage them to drink water with a pinch of salt. The patient needs time to rest and get fluid back into circulation.
What it is: Heat stroke is a life-threatening emergency that results from the body’s core temperature rising to at least 105 degrees Fahrenheit. Unlike heat exhaustion, which is fundamentally a dehydration problem, heat stroke is a brain problem; the brain is literally cooking.
Signs and Symptoms: In addition to the signs and symptoms of heat exhaustion, a person suffering from heat stroke experiences an altered mental state; this change is the critical differentiator between heat exhaustion and heat stroke. This altered mental state manifests in disorientation, irritability, and combativeness along with loss of coordination and, as heat stroke progresses, sometimes seizures. Importantly, these signs of altered mental state can occur without prior signs of heat exhaustion.
Treatment: It is imperative to aggressively cool a patient with signs and symptoms of heat stroke. Move the patient to shade and remove restrictive or insulating clothing or gear, like a backpack, neck wrap, or hydration vest (cotton clothing is okay). Get the patient wet and fan them aggressively. Place ice packs at the patient’s neck, armpits, and groin. Encourage the patient to drink water as soon as their mental state allows for autonomous fluid intake. Anyone suffering from heat stroke needs professional medical help as soon as possible.
What it is: Hyponatremia is the condition of inadequate blood sodium levels. It results from consuming too much water and too little sodium, such as when a hot-weather adventurer drinks lots of water without consuming any food.
Signs and Symptoms: Hypotnatremia’s signs and symptoms are nearly identical to those of heat exhaustion, but treatment differs. Differentiating between the two requires diving into the patient’s health history: has the patient consumed ample to excessive water, eaten little to no food, and urinated regularly to frequently? If so, suspect hyponatremia. The patient suffering from heat exhaustion generally is dehydrated, so their recent water consumption will be low, their urination infrequent, and their urine yellow to dark yellow.
Treatment: Treat a hyponatremic patient by giving them salty snacks and ceasing water intake until their condition improves. Move them into the shade and allow them to rest. Avoid electrolyte replacement drinks, as a patient suffering from hyponatremia already has too much fluid relative to sodium in their system and the concentration of sodium in electrolyte drinks is too low to swing the ratio back in the right direction.
Experiencing any heat-related illness can, at best, inconvenience an adventure or, at worst, endanger a life. But importantly, preventing these illnesses is fairly straightforward with a little diligence, and the same prevention principles apply to all of the above conditions. Most of these principles are admonitions every adventurer has heard many times, yet most heat-related illness results from failing to heed one or more of them.
>> Slow down! Heat makes everything more difficult for our bodies. Especially if not adapted to heat, modulate your effort. Back off to a point where your effort is maintainable without redlining, which will likely be a much slower pace than in cooler weather. A good gauge on effort level is the ability to speak in sentences; any pace that prevents carrying on a conversation is likely too fast for hot conditions, especially if not heat adapted.
>> Drink water to thirst and snack regularly. Drinking small amounts of water at regular intervals allows our bodies to absorb fluid more effectively than infrequently drinking large quantities. Regularly consuming a variety of salty and sweet snacks keeps blood sodium levels healthy and prevents hyponatremia. Remember that in arid climates, fluid loss is more difficult to notice, as sweat evaporates quickly compared to more humid climates. Consider setting a reminder on a phone or watch or recruiting a friend’s help to remember to drink regularly in hot climates.
>> Staying wet is the best way to stay cool. Take advantage of creeks and rivers for submerging your body and soaking clothing. Bring enough water to pour some over your head periodically. Consider wearing cotton; because it dries more slowly than synthetic fabrics, it keeps us cooler longer. Bring a bandana or neck wrap to soak and wring out over your body when possible, then soak it and wear it around your neck until it dries.
>> Protect your skin from the sun. Wear a large-brimmed hat and loose, thin, light-colored long-sleeved clothing. Loose, thin clothing and a wide hat brim minimizes the need for pore-clogging sunscreen that can make you feel clammy and provides superior UV protection (how many of us really remember to reapply sunscreen as often as we should?).
>> Avoid adventuring in the hottest part of the day. Explore in the morning and evening, and seek shade during the mid-day sun.
Guidance on exactly how much water to drink while adventuring can be extremely confusing. Perhaps you’ve heard a guide tell you to “drink before thirst” (sometimes helpful, sometimes encourages dangerously high fluid consumption) or seen a marketing campaign instructing you to “hydrate or die” (technically true, but again, fraught). The official guidance today from a contingent of wilderness medical professionals is “drink to thirst,” as mentioned above, while bearing in mind that the recommendation is not “wait to drink any water until desperately thirsty.” The recommendation is simply to drink when you feel like it plus maybe a little more, which, in all likelihood, will be a few times per hour while doing moderate physical activity in hot conditions.
The recommendation to drink to thirst is specifically worded to discourage the forcing down of copious amounts of water, especially without also consuming salty foods, which can lead to hyponatremia. All this guidance basically distills into a few bits of info:
Drink when you feel like it, and snack consistently.
If you need a metric, aim for .25 liters of water every 15-20 minutes while exercising in hot conditions. 
Don’t force yourself to drink gallons of water above and beyond the above recommendations.
Slowing down, pausing to soak your clothing, and avoiding the hottest part of the day may slightly complicate your adventure logistics, but the logistical complication is infinitely tinier than needing an emergency room when you’re hours and many trail miles away from one. Safe outdoor adventure is possible even when temperatures soar, especially for those willing to find adventure in exploring the world beneath the shade of a desert juniper during the day’s hottest hours.
Foot Notes / Source Credit:
 Buck Tilton, Wilderness First Responder (Morris Book Publishing, 2010), 126.
 Tilton, Wilderness First Responder, 124.
 Tilton, Wilderness First Responder, 126.