Ep. 33 - Heat Illness Fundamentals: Recognize the Spectrum, Cool First, Transport Second

Dr. Patrick Fink reviews the spectrum of heat illness using 2024 Wilderness Medical Society guidelines, covering recognition, physiology, field treatment, and key mimics. He distinguishes heat edema, heat cramps (salt-depletion vs exercise-associated), heat syncope and exercise-associated collapse, and defines heat exhaustion by preserved mental status versus heat stroke by altered mental status in a heat context, warning not to wait for a temperature threshold. He explains heat stroke pathophysiology as direct thermal injury plus a sepsis-like inflammatory cascade from gut hypoperfusion and barrier failure, emphasizing “heat × time” and a 30-minute cooling window. Core management is “cool first, transport second,” with cold water immersion as gold standard and improvised “tarp taco” alternatives; stop cooling around 38.3–38.8°C, avoid antipyretics and dantrolene, and use fluids only as support. He highlights exercise-associated hyponatremia as a dangerous mimic requiring hypertonic saline, and discusses disposition, including possible field release after full recovery within two hours for healthy exertional cases.

Links

Episode 27: Thermoregulation: The Physics and Physiology of Body Temperature Regulation

Wilderness Medical Society Clinical Practice Guidelines for the Prevention and Treatment of Heat Illness: 2024 Update

Chapters

00:00 Heatstroke Trail Scenario
01:02 Episode Roadmap
03:34 Thermoregulation Basics
06:43 Mild Heat Illness
11:21 Heat Exhaustion Line
13:32 Heat Stroke Recognition
17:18 Why Heatstroke Kills
22:37 Cool First Transport Second
24:51 Cold Water Immersion
27:31 Improvised Field Cooling
28:28 Myths Meds and Fluids
33:56 Hyponatremia Mimic
36:57 Disposition and Transport
39:38 Gear and Preparation
41:05 Key Takeaways Wrap Up

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Transcript

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Patrick Fink 0:05

Picture this. It's the third afternoon of your desert canyon trip, and the temperature gauge on your pack is reading one oh three Fahrenheit. You've got one more climb out of the wash before camp, maybe eight hundred feet of vertical, loose, sun-baked switchbacks. Your partner, a strong twenty-four-year-old who's been out front all week, has gone oddly quiet. You notice he's stopped drinking water. He's swaying a little bit on the trail, and when you ask if he's okay, the answer doesn't quite make sense. He calls you by the wrong name, and then he sits down in the middle of the trail in full sun and starts tugging at his shirt, agitated, like he can't get comfortable in his own skin. His skin is hot, burning hot. You've got maybe thirty minutes before this gets much, much worse, and what you do in the next half hour is gonna decide how this story ends. Not a helicopter, not the hospital, you Hello, and welcome back to Wilderness Medicine Updates, the show for providers at the edges. I'm your host, Dr. Patrick Fink. Today we're going to dive into the full spectrum of heat illness, everything from the mild stuff that can ruin an afternoon all the way up to exertional heat stroke, which is a true time-critical emergency that you can absolutely die from and that you can absolutely survive if the people around you know what to do. This one's been a long time coming. Way back in episode twenty-seven, we did a deep dive on thermoregulation, the physics and physiology of how the body manages its own temperature. I told you then we'd come back around to the heat side of things when the season turned, and here we are. So if you want the full foundation under today's episode, go back and listen to twenty-seven first. I'll put a link in the show notes. But if you don't have time, no problem. I'll give you the recap that you need as we go along here Here's what you can expect to learn today. First, we're gonna talk about how to recognize each rung on the ladder of heat illness, heat edema, heat cramps, heat syncope, heat exhaustion, and heat stroke, and why telling them apart actually matters. Two, we're gonna dive into the physiology and the pathology, what's really happening inside a heat stroke patient, because understanding the why is what lets you make good decisions when the situation gets weird. Third, and most important, we're gonna talk about pre-hospital treatment, what you do in the field with the gear you actually have to be able to save a life. And four, we'll discuss the one diagnosis that can fool you into doing exactly the wrong thing and talk about how not to fall for it. I'll be grounding this episode in the Wilderness Medicine Society's clinical practice guidelines for heat illness. They put out an updated version in twenty twenty-four, and like all the WMS guidelines, it's open access. There's a link in the show notes, and I'll give you a disclaimer up front, you know, this is education, not medical advice. And before you change anything about how you practice, talk to your medical director. Some of what I'll tell you about field cooling is frankly a little bit ahead of where most EMS protocols currently sit, and we'll talk about that too And a quick note on the scope of this podcast. When I talk about heatstroke today, I'm mostly talking about exertional heatstroke. That's the kind of thing that happens to a healthy person working hard in the heat. That's the one you're likely to see in the backcountry, on a fire line, on a SAR call-out, or at a race. We'll touch on the classic passive kind too, of like a little old lady sitting in a hot apartment with no AC, but the field game is really built around exertional heatstroke. Now, let's dive in. Let's set the table with a little physiology because everything downstream depends on that. Your body runs at about thirty-seven degrees Celsius. That's ninety-eight point six degrees in freedom units. Your hypothalamus is your thermostat. It's reading the temperature of your blood and your core far more than the temperature of your skin. When your core temperature starts to climb, and I mean by even less than a single degree, the hypothalamus fires off two responses to dump heat. The first is the big one. It opens up the blood vessels on your skin. At rest, your skin gets maybe a quarter liter of blood per minute. But if you crank up the cooling demand, that blood flow can climb to eight liters a minute, which is a massive fraction of everything that your heart is pumping, redirected to the surface to try to radiate that heat away. The second response is sweating so that heat can leave by evaporation. Here's a part to hang on to. To send all that blood to your skin, your body has to take it from somewhere. It's a zero-sum game, and a big chunk comes from your gut. Splanchnic and kidney blood flow drop by about thirty percent when you're working hard to cool off. File that away because that underperfused starved gut is gonna come back as a main character when we talk about why heat stroke is so dangerous. As a reminder, there are four ways that your body and the environment trade heat: conduction, which is by direct contact; convection, which is moving air or water carrying heat to and from the body; radiation, which is the infrared heat that comes off of any warm object; and evaporation, which is sweat turning into vapor and pulling out heat with it. Here's the tough catch when we're talking about heat. Conduction, convection, and radiation only move heat downhill from hot to cold. So once the air around you gets as hot as your skin, say thirty-five degrees Celsius, mid-nineties Fahrenheit, Those three don't just stop helping you cool off, they reverse. Now the environment is shoving heat into you, and at that point, evaporation is the only tool you've got left to cool the body. And evaporation has its own kryptonite, and that's humidity. When the air is already saturated with water, your sweat can't evaporate. It just drips off you, useless. That's why a hot and humid day is totally a different animal from one that's hot and dry, and why when you dump water on the sauna and suddenly it's steamy, your core temperature is gonna start to climb faster. In the dry heat, you can sweat your way out of trouble for quite a long time. But in humid heat, your last cooling mechanism is gone. That's also why the right way to measure heat risk isn't just purely a thermometer. It's a measure called the wet bulb globe temperature, which folds in humidity and solar load. WS gives us their kind of highest recommendation for how to measure heat risk, but plain old heat index is the generally more available cousin. Either way, the lesson is the number on the thermometer can undersell the danger if it's a still, humid, and sunny day. Okay, so that's the basics. Now let's break it one stage at a time. We'll start with the mild end: edema, cramps, and syncope. The first thing to understand is that heat illness is a spectrum. It's not a staircase that you climb one step at a time. People often slide gently up the mild end and stop, but heatstroke can also hit kind of like a thunderclap out of nowhere without any polite warning of mild symptoms. So you can't ever really tell yourself, "Well, they were fine an hour ago. It can't be that bad." But let's start with the mild stuff and work our way up. Heat edema. This is the most benign thing on our list. Early in a hot trip or early in a heat exposure, someone who's not yet acclimatized to heat can see hands and feet swell up. That's just the combination of all that skin vasodilation to try to cool yourself, plus gravity pooling fluid in dependent extremities. It's harmless. It goes away on its own. You can elevate the limb. Use a little compression if you want. The one thing you don't wanna do is say, "Hey, there's puffy extremities," and treat the patient with a diuretic or water pill. It won't help, and it will just dry the person out. Mostly, this is just a teaching reminder that heat messes up where your fluid tends to accumulate. Heat cramps. Now, here's a place where language can trip people up, so let me untangle it. There's really two different things that people call heat cramps. When heat cramps were first described back in the 1930s, it was in miners and, like, iron foundry workers who were sweating buckets for hours. And in these people, they saw big, generalized whole muscle cramps, and this was tied to both salt and water depletion. And those kinds of cramps respond to salt, like an oral electrolyte solution or even a salty snack. But generally speaking, the cramp that a runner gets, for example, in their calf at mile twenty of a trail marathon, um, that's a different beast. That's exercise-associated muscle cramps, and most often that's from neuromuscular fatigue, and it's not a salt issue. So that one responds better to stretching, not electrolytes. Why do we care about this distinction on a wilderness medicine podcast? Because it forks the treatment. If you pump salt into a fatigued runner, you're kinda treating a problem that they don't have. And if you are, you know, just stretching someone who's been working super hard in the heat on a fire line, dumping sweat into their, uh, fire-resistant clothing, you're missing their issue. So you need to mac-match the mechanism to the patient, and the treatment follows Heat syncope. This is fainting. Someone who's been standing in the heat or they just stopped a hard effort and they have all their skin blood vessels dilated, blood pooling in their legs. For a moment, they can get just not enough blood to their brain, and so they will collapse. But the key is that they come right back when they're horizontal. So the patient goes down on the ground, you lay them flat, you lift their legs up, and they wake right back up. By definition, this is a benign thing, uh, but this is where it gets a little sticky because heat syncope ends up being a little bit of a diagnosis of exclusion. Before you wave off someone's fainting episode as being heat syncope, you have to consider the potential that they could have fainted from a cardiac cause. You have to make sure that they didn't hurt themselves in the fall. And there's a cousin here that's worth naming, which is exercise-associated collapse. And that's a runner who, you know, at the end of a race, crosses the finish line and then crumples. And that's because when the leg muscles stop pumping, uh, the heart starts to slow down, blood pools in the extremities, venous return drops, and down they collapse. And that can happen with a totally normal body temperature and normal hydration. Again, lay them down, put their legs up. They usually come around. The red flag for the whole category here when we're talking about fainting is someone who actually faints during exertion or someone who faints over and over with no good explanation. Those people need a cardiology workup. They need their heart looked at because there are case reports of heat unmasking electrical conduction issues like Brugada syndrome, which can cause sudden cardiac death by kicking off dangerous arrhythmias. So exertional syncope, particularly recurrent exertional syncope, is something that needs investigation and which shouldn't be just kept in the field. So that's the mild end. Annoying, mostly self-limited, treated with rest, shade, fluids, just kinda common sense. Now let's cross into the territory where you have to pay a little bit more attention Heat exhaustion. Heat exhaustion is defined by what is still working. Heat exhaustion is when the body is hitting a wall. It's a combination of cardiovascular strain, all that blood that's been shunted to the skin, and thermal strain, and it shows up as weakness, deep fatigue, intense thirst, headache, nausea, dizziness, maybe feeling a little faint. The core temperature can be normal or slightly elevated, but it's still gonna be below forty degrees Celsius, below one oh four Fahrenheit. But here's the single most useful thing that I can tell you about heat exhaustion, and I want you to write it down inside of your brain. Heat exhaustion is defined by the fact that the patient's mental status is still intact. They can be miserable, they can be wrecked, maybe a little, like, dopey from just sheer exhaustion, but they should be oriented, they should know who and where they are, they should make sense when they talk to you. The preserved mental status is the line between heat exhaustion and heat stroke. The moment that the brain starts to get screwy, you're not dealing with heat exhaustion anymore. So heat exhaustion is kind of like the body's emergency brake. It's forcing you to stop before you overcook yourself, and most of the time, it resolves beautifully. If you get a patient with heat exhaustion symptoms out of the sun, stop the activity, sit them down somewhere cool, give oral fluids, isotonic fluids if you have them, or water plus some salty food. As they cool off, you'll watch them get better. But here's kind of the idea that you have to hold in your head, which is that heat exhaustion is both the off-ramp and the on-ramp to more serious heat illness. So if you treat it well, it can be the end of that patient's story, but if it's ignored and this patient is allowed to remain in the sun or they're pushed to keep going, it can roll right on into heat stroke. So if you recognize heat exhaustion, you need to treat it actively. You don't just let someone tough it out on the trail in the heat. You need to intervene and watch, and if they're not turning the corner, then you need to escalate your concern. Heat stroke. This is the one that kills people. The textbook definition of heat stroke is a core temperature above forty degrees Celsius or one oh four Fahrenheit plus central nervous system dysfunction That central nervous system piece can look like a lot of things. It can be confusion, agitation, combativeness, bizarre behavior, slurred speech, the staggering drunk-looking gait we call ataxia, seizures, or a full-on coma. There are two main flavors of heatstroke. The what's called classic heatstroke or non-exertional heatstroke is a passive situation. It's when heat overwhelms a vulnerable person who isn't doing anything strenuous. The classic case here is elderly folks in a heat wave with no air conditioning or very young people with chronic illnesses or people on certain medications. It comes on slowly over the course of days, and these people, uh, have classically s-stopped sweating, and they have hot, dry skin, become altered, and that's how a heat wave can end up causing significant mortality. Exertional heatstroke, on the other hand, is our other flavor, and it's the one that we care about in the field. This is when endogenous heat, heat your own muscles are creating, is being cranked out faster than your body can dump it. It hits young, healthy, fit, motivated people like athletes, soldiers, wildland firefighters, a SAR member carrying a litter uphill, a hiker pushing up that last climb in the sun, and it comes on fast. These folks are often still dumping sweat, and they tend to have a lot more kind of muscle breakdown going on. This is our patient from the opening of this episode. So let's spend a minute on why this magic number, forty degrees, is a little bit of a liar because it can trip up even experienced people in both directions. First, you can have high temperatures without illness. If you stick a rectal thermometer in a bunch of marathoners at a finish line, hopefully you're paying them, somewhere between fifteen and fifty-five percent of them would have a rectal temperature over forty degrees Celsius, and about ten percent would be over forty-two degrees Celsius, and yet they're totally fine walking around asking where to find a bagel. So a high number all by itself in a person who looks and acts normal is not heatstroke, and guidelines are pretty explicit. We don't slap a pathologic label on an asymptomatic person just because of the temperature. The second direction is the one that's more dangerous, and this is a, someone with a quote unquote normal temperature that's actually heat stroke. Because by the time you get a temperature in the field, the patient may have already started cooling. They're in the shade, you've pulled their shirt off, time has passed, and so a reading under forty degrees Celsius doesn't let you off the heat stroke hook if the story and altered mental status are suggesting otherwise. So here's how you actually have to think about it in the field, and I'm gonna say it twice because it's that important. The thing that should trigger you to start aggressively cooling someone is not a thermometer reading, it's the combination. A person who's hot, whose mental status is altered in a setting where heat exposure makes sense. Hot plus altered plus a plausible heat story equals treat for heat stroke right now. The WMS says it pretty plainly, "In a hot patient with an altered brain, do not delay cooling waiting on a temperature that might read below some threshold." It's a clinical recognition. The number helps to refine your picture, it helps to communicate the patient's situation and track changes over time, but it doesn't gate your action. All right, now let's get nerdy. Let's talk about what's actually cooking in a patient with an exceedingly high temperature, because this is the part that helps everything else make sense. Why is heat stroke so lethal? What's actually going on inside this person? Let's talk about the pathophysiology. There's two things that are happening at once and running in parallel, and they both come back to the one main issue, which is heat multiplied by time. The first insult to the body is direct thermal damage. Above a critical temperature threshold, and it's a dose, not really a hard line, but think, you know, roughly forty-one and a half to forty-two degrees Celsius sustained, heat literally starts cooking your cells. Proteins unfold and stop working. Cell membranes lose their integrity. Ion pumps fail. Mitochondria, your cellular power plants, break down and start spewing out reactive oxygen species instead of producing energy. This is thermal energy... this is thermal injury at the molecular level, and crucially, how bad it gets depends both on how hot you got and how long you stayed there. That's the whole ballgame. It's the area under the curve Now, your, your cells aren't defenseless. They make these beautiful things called heat shock proteins, which are these molecular chaperones whose whole job is to grab denaturing proteins and refold them, prevent them from clumping. They stabilize membranes. They protect your gut lining. They're a benefit that you get if you use saunas is upregulation of heat shock proteins. And when you've got a robust heat shock protein response, you're protected, and that's called thermotolerance. And this single fact explains a ton. It's why heat acclimatization can help protect you. It ramps up these proteins. It's why the elderly and the unacclimatized are vulnerable. Their response to heat is blunted. And it's even why genetics matter. Some people are just more susceptible. This is also why a bout of heat stroke can leave you more vulnerable to heat illness for months afterwards because it actually resets all these adaptations. It kind of fries the system. When your heat shock proteins get overwhelmed, the cooking wins and cells start to die The second heat insult is where heat illness turns into something that starts to look like sepsis. Remember that when your blood starts to redistribute to your extremities, it starves your gut. It drops that blood flow to the gut by thirty percent. Now add that direct heat injury to the intestinal lining, and the result is a leaky gut. What's leaking out is endotoxin, lipopolysaccharide from bacteria that live in your intestines. Now all of a sudden, that endotoxin can cl-cross into your bloodstream, and your immune system reads it as a massive infection. It mounts a full systemic inflammatory response, a cytokine storm. The same mediators that you see in sepsis all start surging within the bloodstream, and that inflammation injures the lining of the blood vessels, makes them leaky. You drop your blood pressure, you light off your clotting cascade and start consuming your clotting factors, and it causes a complex problem called disseminated intravascular congestion. There's a clean way to frame this that reach- researchers call the dual pathway model, and that's that above forty degrees, you've got these two independent processes running. The direct cooking, the heat toxicity, and the gut endotoxin-driven inflammation, what some people are now calling heat sepsis. And they run side by side and converge on the same nasty endpoint, which is injured blood vessels, failed clotting, and multiple organs shutting down. And which organs? The brain takes a hit. The hypothalamus, the cerebellum, the hippocampus, they're all especially heat sensitive, which is why you start getting ataxia and confusion early in heat illness, and why people who survive heat stroke can be left with lasting cognitive and motor deficits. Muscles break down, causing rhabdomyolysis, which dumps potassium and myoglobin into the blood. And then the kidneys start to fail from a combination of low blood flow, that myoglobin, and the inflammation. The liver is also exquisitely heat sensitive and can fail. And this is the sneaky bit that always shows up with the liver, which is that this issue can show up several days later. So someone who looks like they've recovered from heat stroke can have a delayed liver failure forty-eight to seventy-two hours down the line And the cardiovascular system, which started out by pumping like crazy to try to cool you down, eventually collapses into shock. So heat stroke mortality for these reasons runs around 10%, even with good care. And if the patient that you are treating is showing up hypotensive, low blood pressure, that mortality triples to around 30%. I'll be honest about the limits of what we know, because that's what we do here. This like gut endotoxin story is best established in classic heat stroke patients. In some exertional heat stroke models, the gut gets leaky, but they don't always find a lot of measurable endotoxin. So exertional heat stroke might lean a little bit more towards the like directly cooking your body with heat side of things. The science is still being worked out, but the core picture, which is heat plus inflammation that scales with the duration and the magnitude of that heat, that's still a solid mental foundation. So let's pull all that physiology into the single most important sentence in this episode. The damage from heat stroke is a function of how hot you got times how long you stayed there. It's the area under the curve. It's not just the peak temperature, it's the temperature and the time And that right there is why the entire pre-hospital treatment of heat stroke reduces into four words, cool first, transport second. Think about what that means. If the injury is heat times time, then the single most powerful thing any human being can do for this patient is to take away the heat as fast as possible, as early as possible. So that means treating on scene, not after a forty-minute drive to a hospital or a prolonged extrication. The number that gets tossed around borrowed from the sports medicine world is this, you wanna get the core temperature under about forty degrees C or one oh four Fahrenheit within thirty minutes of that patient collapsing. It's called the golden half hour, and the payoff here is pretty staggering. Military and athletic programs that immediately immerse exertional heat stroke patients in cold water report essentially zero mortality. Zero. So if you can cool people fast, people just live, and that's what you get, the prize you win for being able to do that. So let's talk about the pre-hospital treatment. Let's get practical. You've got the patient from the start of this episode, hot, altered, sat down in the sun. What do you actually do? Like everything in medicine, let's start with the airway, breathing, and circulation. If there's a life threat there, you address it. If they're seizing, protect them. If they're unconscious, may need to manage their airway or be prepared for vomiting or aspiration. But assuming that we've handled these immediate ABCs, the primary treatment is cooling. Everything else is supportive. Cooling is the medicine, and the principle is you wanna cool on site before you evacuate. Don't load and go and cool on the way. The evidence and the guidelines have flipped that old instinct on its head. You cool them wherever they dropped, get that temperature down, and then you worry about transport. First cool, then transport So what's the best way to cool? The gold standard, and the one that the WMS gives their strongest possible recommendation, is cold water immersion, dunking the patient in a tub of ice water. So let's talk about why this wins, because the physics is just beautiful. Water conducts heat about twenty-four times better than air, twenty-four times. So immersion is conduction operating at full throttle with a huge temperature gradient between cold water and a hot body that will drive heat out fast. And the colder the water, the faster the cooling. Ice water is ideal, but if you can't manage ice water, just use the coldest water that you've got. Let's put some real numbers on these cooling methods because it's where it gets concrete. So cold water immersion, your ideal rate is it will cool a patient about point three five degrees Celsius per minute. And in big real world studies of like two hundred and fifty plus exertional heat stroke patients, this practically settles out to actually about a quarter of a degree per minute. So roughly a degree every five minutes. If you need like a rule of thumb, you can remember about a degree Fahrenheit every three minutes. If you can get the patient in cold water and you can kind of keep that cold water moving around the patient. The tarp method, which I'll describe in a second, gets you about point one four to point one seven degrees Celsius per minute. And weaker things like dousing the patient and fanning, ice packs, a cold shower, all come in under point one degrees Celsius per minute. So immersion is two to three times faster than the alternatives, and that speed is what you're buying. That speed is the patient's survival. So technique here matters. We want to strip off any in-insulating clothing and gear and try to get the trunk and the limbs into the water from the neck down. And here's a small detail that people can miss, which is that we want to keep the water moving, stir it, agitate it. If you let the water sit still against the skin, it warms up into a little insulating layer and your cooling rate slows. If you've ever done a cold plunge, you might have appreciated this. If you climb into still cold water and you stay super still, it actually starts to feel more comfortable. But if you're then in a fancy kind of cold plunge tank and the little circulator kicks on, all of a sudden it gets a lot colder. So keep the water around the patient churning. Two things never to do, don't let the head go under water, and don't leave the patient alone. I shouldn't have to tell you this because they can seize, they can aspirate, they can drown. Have hands on them the whole time. And if you're fancy and you have a rectal probe in place, you can now cool by the numbers But Patrick," you say, "I'm in the backcountry. I don't have a big stock tank full of ice." Fair. So let's talk about improvised cooling because this is where wilderness providers can earn their keep. There's a technique called the tarp taco. You lay the patient on a tarp, and you dump whatever ice and water you have in there, and people hold up the edges of the tarp to make a tub. You slosh that ice slurry around and over the body. A fluid-impervious body bag works the same if you've got one. This is what we used to do at the university hospital in Utah, a body bag. No tarp? Okay, maybe you have a natural water source, a stream, a snowmelt pond, a lake. Those can work. We just need to protect the patient from submersion, floating away in the current, what have you, and don't let go of them. If all you have is cold water and bottles or snow on the ground, then douse the patient repeatedly, and you pack snow on and around them. Use what you've got. The point is relentless, aggressive, whole-body cooling by the best means available. Now let's talk about shivering. Let's kill this zombie because this myth refuses to die, and it makes people cool too timidly. The myth goes that if you put a heat stroke patient in cold water, they'll shiver and their blood vessels will clamp down, and that will trip, trap heat or even raise their core body temperature. You might hear this, and it's wrong. It traces back to a misreading of an eighteenth-century observation called the Currie response, which is a tiny bump in, um, normal temperature volunteers when they start shivering. But your heat stroke patient isn't a normal temperature volunteer. Their thermoregulation is failing, and so their shivering response is blunted or gone, and the idea that shivering meaningfully fights your cooling has been somewhat physiologically debunked. So let's be blunt. The fear is theoretical, and the benefit of cooling is proven, and you should not let some fear of shivering slow you down for a second. Get them in the water. And while we're busting myths, let's talk about ice packs. The old teaching is to, like, slap chemical cold packs or ice packs on the neck, the armpit, the groin, over the big blood vessels. Turns out that's pretty low yield. It's tiny surface area, not much contact, not much cooling. Guidelines have actually moved away from it. If you're using ice or snow, the move is to cover as much of the whole body as you can to maximize that conductive surface area. Those chemical cold packs are kind of weak sauce. They just don't absorb enough heat. If you're gonna use them at all, the more interesting data says put them on what's called glabrous skin or the hairless skin of the body, the cheeks, the palms, and the soles, because those areas have special high-flow blood vessels called arteriovenous anastomoses that kind of act like radiators. That glabrous skin is a far better place to dump cold than the neck and the armpits. So do whole body ice or snow if you can or immersion, but glabrous cold skin packs are a distant backup. Stop wasting your efforts by tucking, you know, ice packs in the armpits. Question I hear sometimes is when do you stop cooling? Because this surprises people. You don't want to cool the patient all the way back to normal. The target for cooling is actually thirty-eight point three to thirty-eight point eight degrees Celsius, call it a hundred and one Fahrenheit-ish. Twenty nineteen guideline phrased it as no less than thirty-nine, and thirty-eight point six is the classic number for athletics. So why stop short of normal? The-- Two reasons. One is momentum, which is conductive cooling keeps working after you pull the patient out because the skin remains cold and the core body temperature needs to equilibrate. So if you chase a normal reading, you can overshoot them straight into hypothermia. It's almost analogous to after drop in a hypothermic patient. And second, around that temperature, the body's own thermoregulation starts to kick back in, and it can finish the job of cooling. So don't overshoot. Just get the patient back to pretty hot. And at that point, we can remove our aggressive cooling tactics. There is a little bit of a practical gotcha here, which is that in the recovery phase, a rectal temperature can read falsely high because the body m-mass insulates the probe. So don't keep frantically cooling a lagging number if the patient is clinically improving. How about fluids? Exertional heat stroke patients are often dried out, so isotonic fluids like normal saline, a liter or two are reasonable. If they're obtunded, unresponsive, or seizing, it's definitely safer to give this to them IV than trying to give it to them orally. But two cautions here, don't overhydrate, particularly anyone with a heart history because you can flood the lungs. And here's another big one, which is that you should never delay cooling to try to hydrate the patient. Fluids are a supportive measure, but cooling is the essential treatment that addresses the core issue. If you have cold IV fluids, great. That's a nice adjunct. You know, it might help a little bit, but you're never gonna cool a patient down with IV fluids alone And there's two medications which you may be tempted to use, which you just shouldn't. The first are antipyretics, so fever medicines, Tylenol, ibuprofen, aspirin. These are useless here and potentially harmful, and here's why. Antipyretics work by lowering a raised thermostat setting. They're addressing the brain's kind of set temperature. That's what fever is. Your hypothalamus has d- deliberately cranked up the set point to fight an infection. But heat illness isn't fever. The body's set point hasn't been raised. The body is trying desperately to cool down and is just losing the fight, so there's no raised thermostat to try to turn down. The drug does nothing for your temperature. So in the stressed kidneys, in the stressed liver, we just don't need to hit them with Tylenol and NSAIDs. Just skip them. And the second is a medication called dantrolene. This is a medication that we use for malignant hyperthermia, which is basically runaway muscle metabolism in people who've gotten gas anesthesia outside the scope of what we need to talk about here. But it has been tested in classic heat stroke, and it has been shown to do nothing for, um, helping with the cooling rate or the outcome, so it's not recommended. It is currently being studied for exertional heat stroke, but it is not current practice The mimic. Now, let's talk about the diagnosis. I... Let's talk about the diagnosis I promised would try to fool you. This is so important that if you take one clinical pearl from this whole episode, make it this one. If you have a collapsed, confused athlete in the heat, and your brain is screaming heat stroke, you need to also consider exercise-associated hyponatremia or low sodium, and it looks almost identical. Patient is confused, they have a headache, nausea, altered mental status, even seizures and coma in an exercising person. Here's the discriminator. It's kind of beautiful in its simplicity, which is that hyponatremia classically shows up without a high temperature. So altered mental status in an athlete who does not have meaningful hyperthermia should make you think sodium, not heat. This is what happens when someone drinks a huge amount of plain water over a long event, and their body holds onto that water inappropriately, their blood sodium drops, and then water starts to shift into brain cells, causing the brain to swell. It's an emergency. So you might see why this matters so much. Your instinct with a collapsed athlete might be to push fluids, and if it's hyponatremia, plain water or even normal saline can make it worse. It can kill them. And dunking a normal temperature hyponatremic patient in ice water does not do anything for their real problem. So if you get this wrong, you can hurt them. What do you do if you suspect hyponatremia, and you can't check a sodium level in the field? The answer is the opposite of what you'd usually do for a dried-out hiker. You're gonna give hypertonic saline. That's three percent saline. You give up to three hundred milliliter boluses about ten minutes apart until mental status improves, and then you're gonna move quickly to definitive care. It's one of the very few times that, like, giving salty fluids in the field is exactly right. You're gonna be able to confirm with a sodium level later. And hyponatremia isn't the only mimic. Like, run the list in your head. Check a blood sugar. Hypoglycemia is cheap and reversible. Think seizure or head injury. Did they fall or hit their head, or did the head injury cause them to fall? Think about drugs and toxins, things like stimulants or serotonin syndrome that can cause hyperthermia themselves. And make sure to, like, spend a half second thinking about infection because real sepsis looks like heat sepsis, but it has an infectious source. Think thyroid storm in an appropriate patient. And if you're up high, think about high altitude cerebral edema as a potential confounder. You treat the heat triad aggressively, but you want to keep these in your mind. The WMS field algorithm builds this right in. If the picture doesn't fit or there's altered mental status without clear hyperthermia, then it's time to step back and consider alternatives instead of tunnel visioning on heat just because it's hot outside Now let's talk about disposition. Who stays and who goes after you've cooled them? Who goes to hospital? Who can be in the field? The twenty twenty-four guideline actually gives us something new and useful here. For a healthy person who has exertional heat stroke, who gets good field cooling, and whose mental status and mobility return to baseline within about two hours, the guidelines suggest that they can be released to self-care without a hospital trip. That's the kind of formalized version of what athletic events have done for years. Like, cool them down, and if they return to normal, then you can street them. Now, that's a weak recommendation, and it requires a healthy person, a clear exertional cause, and a genuine complete return to normal, so you should use judgment here. Let's flip it around. If it's classic non-exertional heat stroke and the patient has any medical comorbidities like heart disease, diabetes, they're elderly, they're on predisposing medications, then they need to get transported to a higher level of care, even if they respond well to your cooling. Their physiology just doesn't tolerate a field discharge. And remember that delayed liver issues can arise, there can be clotting failure, there can be kidney failure, and those can be somewhat delayed. So that's a strong recommendation. If it's classic heat stroke, the kinda slow one, or they have significant comorbidities, then they should go to the hospital. For mild stuff, if you're treating what you think is heat exhaustion and it's not getting better or it's getting worse, the updated move is to stop and reconsider the diagnosis, reexamine the patient, rather than just cranking up the cooling. If there's no improvement within about fifteen minutes of trying to address this patient who's getting worse, then we need to focus on emergent transport. If-- when is transport just non-negotiable? If you can't cool effectively in the field, when altered mental status won't resolve, when you have worries about multiple organ systems, when it's classic heat stroke or they have significant medical comorbidities, when you suspect hyponatremia and the patient's gonna need labs, or honestly, whenever you're not sure what's going on. One more thing on this, and it's a real-world frustration. When you hand this patient off to EMS, you have to explicitly tell them what cooling you've already done and push for that cooling to continue on the way to the hospital. Because there's an uncomfortable truth here, which is that a lot of EMS protocols around the country still don't authorize pre-hospital cold water immersion, and some literally say, like, "Don't delay transport to cool," and that's the opposite of the best evidence. So you wanna know what your local EMS protocols are and potentially have this conversation with your medical director and your local EMS service before you're standing over a heat illness patient. Again, talk to your medical director before you change your practice based on a podcast. So what does all this mean for what you actually carry in the field and how you prepare to treat heat illness? Honestly, the most important tools here aren't that exotic. A rectal thermometer that reads high enough can be useful. Uh, it's nice to know where the nearest water is on your route. A tarp or a body bag that you have and already know how to turn into a tub. So if you're running a SAR team or you're running a race, an actual immersion tub and the staffing to be able to use it on site is great. The ability to deliver ice water and a tarp or body bag to multiple points on your course is great. And make sure that you've got the mental model that we just built kinda loaded and ready to go. 'Cause here's the thing about heatstroke. It can happen fast, and the patient can't advocate for themselves 'cause their brain is just toast. So the clock is the enemy, and this is exactly the kind of emergency where you don't just, like, rise to the occasion, you fall back on your preparation. So do what we always talk about in this show, kinda run the scenario in your head before you ever need it. Picture the hot, confused athlete on the trail. Picture yourself removing their gear, building the tarp taco, getting them in the water, stirring it, watch the brain coming back online, and just visualize that success until it's a reflex and you have a plan for whatever context you're operating in. Now, let's bring this show home, this mammoth show home with some takeaways. One, heat illness is a spectrum: edema, cramps, syncope, exhaustion, and stroke. And it can hit hard and without warning, so don't get complacent. Two, heat exhaustion is defined by a preserved mental status. Heat stroke is defined by altered mental status. It's hot plus an altered brain plus a heat context. And we don't wait on a thermometer to diagnose this. The recognition is clinical Three, the damage is caused by direct heat cooking plus a sepsis-like inflammatory cascade from a leaky gut, and it scales with how hot times how long, and that's why time matters most. So four, the treatment is cool first, transport second. Cold water immersion is the king because water conducts twenty-four times better than air. Whole body ice if there's no tub, tarp taco in the backcountry. Stir the water, protect the airway, never leave the patient alone. Five, stop cooling around thirty-eight point three to thirty-eight point eight so you don't overshoot into hypothermia. Don't give antipyretics. There's no fever to treat, no dantrolene. Fluids are supportive, but they don't replace cooling. Six, beware the mimic. Altered mental status without hyperthermia means think sodium. Exercise-associated hyponatremia, and the treatment is hypertonic saline, not just more water. And seven, healthy exertional patients who recover fully within two hours can potentially be released. Classic heat stroke patients or those with comorbidities go to the hospital regardless, and we want our EMS services to keep cooling the patients on the way. That's the spectrum of heat illness start to finish. So if you remember nothing else, remember the patient on the trail and remember cool first, transport second. You with a tarp and some ice water are the difference between a scary afternoon with a recovery and a funeral. If you got something out of this episode, single best thing you can do is share it with someone who would appreciate it, a bike patroller, a wildland firefighter, a SAR teammate, an ER doc, nurse, med student, EMT, trail runner, your buddy who guides in the desert. Share with one person today, and you help this show reach more people and more people who need it. And if you've never done it, it takes two seconds. Please give the show a five-star rating on Apple Podcasts or Spotify. You don't have to type anything. It just helps game the algorithm and get the show in front of more ears. I really appreciate it. I love hearing from you. If you have questions, comments, a topic you want me to dig into, or you think I got something wrong, email me at wildernessmedicineupdates@gmail.com. I read everything coming through there. I'm sometimes a slow responder, but I get back to everyone eventually. This is a passion project, and the more people it reaches, the more it's worth doing. So until next time, this is your host, Dr. Patrick Fink. Stay fit, stay focused, and have fun.