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When the Body's Cooling System Fails: Heat Exhaustion vs Heat Stroke

Interviewer: It's time for another edition of "ER or Not," this time with Dr. Graham Brant-Zawadzki, an emergency medicine physician with a subspecialty in pre-hospital and wilderness medicine. In this show, we try to help you figure out if it's a reason to go to the ER, head to an urgent care, see your provider, or handle it on your own.

Today's question: It's dangerously hot out, and someone has been outside for a long time, and maybe they start acting a little confused, maybe they even pass out. Could it be heat stroke? And if it is, is this an emergency or something you can treat at home?

So, Dr. Brant-Zawadzki, let's start with the basics. What is the difference between heat exhaustion and heat stroke?

Dr. Brant-Zawadzki: That's a great question. So anytime you're out in the heat, whether you're exerting yourself or even just at rest, you're at risk for what we call heat illness, and that's a spectrum of disease.

Heat Exhaustion

So heat exhaustion is kind of an earlier part of that, of heat illness beyond just, "I'm feeling kind of uncomfortable and sweating a lot, maybe even a little bit lightheaded." Heat exhaustion is when that lightheadedness becomes more severe, you become nauseous, you might have a headache, and you're just generally feeling unwell, but you're still yourself. And you're still, you know, able to take care of it, and activities, you're just feeling terrible.

Heat Stroke

Heat stroke is the other end of that spectrum as we keep moving down to more severe, and we talk about that when you have neurologic findings. That's when the body temperature rises so much that you start having what we call end-organ damage. That means the brain, the kidneys, and the heart, they're all being affected. And one of the easiest ways for us to recognize this clinically is those changes in brain function. So you might see someone becoming more confused, irritable, agitated, or even unresponsive and lose consciousness.

Interviewer: And so what is actually happening to the body when we hit those more intense levels of heat stroke, when we cross that line?

Dr. Brant-Zawadzki: We are adapted to live in different environments, and, you know, we sweat and we can adapt to hot environments, both in the short term and longer term. That's kind of why early summer always feels the worst. And by the end of summer, we feel like we're a little bit more equipped to be outside and be exerting ourselves. So the body has different mechanisms to help adapt.

But basically, when heat illness occurs, it's a pathological process. It means we've overcome or overwhelmed the body's ability to effectively cool ourselves and maintain that normothermic 98.7-ish degrees that we like to be. And then once those mechanisms are outpaced and overwhelmed, the body temperature starts to ramp up. And that can cause electrolyte problems and shifts. It can cause fluid shifts in our body.

And at extreme heats, we usually only see that when people are both in a hot environment and/or exposed to toxins, like medications or some other illicit drugs. Then, when the body gets above 105, 106 degrees Fahrenheit, we can actually see the proteins in our cells start to denature, and cells start to have true damage.

Red Flags That Signal Heat Stroke

Interviewer: Considering that a lot of this is happening internally, you know, what are the red flag symptoms that we are looking for that, hey, we've crossed into this heat stroke, and this is something serious?

Dr. Brant-Zawadzki: Yeah, so those scary things we're looking for, or those red flags, you're actually going to see someone who may have been pretty sweaty, and then they stop sweating, and so their skin actually becomes dry and hot. That's definitely a concerning sign.

And then, like I said before, those mental status changes. Someone is starting to ask questions over and over again. They seem confused. They seem really tired, just lethargic. You know, they're really hard to motivate to move. And then if they really just stop answering your questions, if they stop responding, if they're mumbling or have slurred speech or lose consciousness, similar to what you might see in a stroke, as we typically see it, where there's not enough blood getting to the brain. That's why we call this heat stroke, because it can manifest with those same neurologic deficits.

Yes, Heat Stroke Means 911

Interviewer: Now, if someone suspects heat stroke, is this something they should go to the ER? Is this a 911 call? How serious is heat stroke?

Dr. Brant-Zawadzki: I would say we always talked about those red flag symptoms, it's almost as if not more important to recognize those early symptoms so you can prevent heat stroke and prevent having to take these more drastic measures. But generally, yeah, if someone is confused, they cannot answer simple questions, and if you have any concern, and they're in a hot environment, it's heat stroke until proven otherwise. And that really is an emergency.

And part of the reason is that it can be very hard to actually cool someone's core temperature back down to a safe level as quickly as it needs to be cooled, and also in a safe manner. So if you suspect a true heat stroke, again, that confusion, mental status change is absolutely a reason to call 911, because it's going to probably take more time and resources than you have available right where you are, depending on the case, to effectively cool that person down both quickly and safely.

What to Do While You Wait for Help

Interviewer: And I know that, you know, we really want to call 911 first. But is there anything that a person can do, when they're starting to see either themselves or someone experiencing this, to kind of keep them under control before help arrives?

Dr. Brant-Zawadzki: Absolutely. So the most effective treatment, again, if someone has heat exhaustion, those early symptoms, other than just getting into the shade, giving them a little bit of cool fluids, is what we call evaporative cooling. And that's part of why we sweat. When we sweat, we put water out into our skin, and then air moving over that water evaporates it, and that dissipates a lot of the heat.

So we can simulate sweating by basically wetting the skin and getting that person in moving air. So one of the most effective ways to cool someone is to actually mist the patient with, like, a spray bottle or any water you have available. And then get them into an area where wind is moving over them, whether just naturally from wind, or if you can set up a fan and kind of fan them off. Even if you're just able to like manually fan, that's actually going to be pretty effective.

And if you don't have like a bottle mister, wetting a T-shirt or a light piece of fabric and putting that over as much exposed skin as you can, again, in the shade, out of the sun, and then getting air moving over that moist skin or moist fabric will be really helpful.

When Evaporative Cooling Works—and When It Doesn’t

Interviewer: Now, evaporative cooling, I mean, is that something that might be impacted by where someone lives?

Dr. Brant-Zawadzki: You know, here in Utah we have a dry mountain environment, and that's where it's going to be the most effective. That's why things like swamp coolers are really effective here in Utah, because that air is so dry. Conversely, I mean, if you're living in Florida or another really humid environment, it's going to be really hard to get that moisture to evaporate off your skin because the air is already saturated.

So, another thing to keep in mind is that you may be starting behind the eight ball if you're in a very humid environment, because that evaporative cooling that our body does naturally, or that we might choose as a tool to cool someone, is just much less effective.

Populations Most at Risk of Heat Stroke

Interviewer: Are there any populations who are maybe more at risk for heat stroke, and what kind of preventative measures should those groups take?

Dr. Brant-Zawadzki: When we study heat waves that occur across the world, we absolutely see some populations that are more affected disproportionately, and that tends to be the elderly, the very young, and those experiencing housing instability. And the reasons for that are not surprising. You know, for when it comes to the very young, they often aren't able to recognize when they're feeling sick. Or if they're very young, they can't move themselves out of that hot environment or treat themselves.

When it comes to the elderly, same thing. Maybe they have some difficulty with mobility. They may not have the support services available. And many of those people are on a lot of medications, and some medications can predispose you to heat illness because they affect your body's ability to hydrate itself and cool itself, like, normally. So we worry about those populations.

And then those, again, with housing instability, they don't have access to air conditioning. They don't have places to go, particularly for shade and water.

So really want to watch out for those patient populations. So if you have some elderly neighbors and it's a particularly hot day or hot time of year, check on them. Or even if you have seen them, just make sure that they have everything they need, that their AC is working, because those are the patients that really suffer in these kinds of environments.

Interviewer: Especially for those groups of people, what are ways that people can prevent heat stroke from getting to that level in the first place?

Dr. Brant-Zawadzki: So we want to just be very conscious of the activities we're participating in. If you are in any of those age ranges or populations, if you're going to be outside, try to pick better times of day. You know, don't go out in the middle of the day or early afternoon. Wait for later in the evening or early morning to recreate, to work outside if you need to.

We always say to hydrate, but hydrating alone is not going to prevent heat illness. And it actually can predispose you to other problems if you're just drinking a lot of plain water out in the heat. So making sure you're drinking to thirst, making sure you're eating as well, getting electrolytes in your body, that'll help your body's natural mechanisms to continue sweating and to help prevent heat illness.

And then, again, having a good plan. Staying in the shade when you can. Knowing where those cooling areas are, if you're at a concert or if you're going to be outdoors for a long time. It's just having a strategy to stay cool.

When It's Time to Go to the Emergency Room

Interviewer: So final diagnosis, ER or not, heat stroke.

Dr. Brant-Zawadzki: Heat stroke is a life-threatening problem, but it's often preventable. We really just need to be careful about monitoring hydration, monitoring our activity levels in heat and in the sun. And the key thing is don't wait for collapse. Don't wait to get to heat stroke. When you start having those early signs and symptoms of heat illness, like lightheadedness, maybe some nausea, muscle cramping, those are warning signs to stop what you're doing, get out of the heat, get out of the sun, cool down, hydrate, get some food and rest, so we don't have to go to the ER.