So far this week, we've talked about basic temperature regulation in the body and we thought about the reflex arc that helps us maintain normal body temperature. Now, we're going to think about what happens when we don't maintain normal body temperature, when the body core gets too hot or too cold. We call those conditions hypothermia, when the body core is below the normal temperature range, and hyperthermia when the body temperature is higher than the normal temperature range. Now, we're going to talk about what those conditions actually derive from, physiologically speaking. So, first of all, hypothermia, a condition in which the body core becomes cooler than normal. Body temperature falls and the normal mechanisms that would go into place would be vasoconstriction of those blood vessels that supply the skin, and then shivering but when hypothermia occurs, those normal physiologic mechanisms aren't enough and the body cools below the normal temperature range. What sorts of conditions do you think might result in hypothermia? >> Maybe if you get stuck in really cold water. >> Being submerged in really cold water for sometimes even as little as one to two minutes, or less, can do it, for sure. Anything else? >> Just being exposed to cold for a long period of time, with wind, without somewhere sheltered. >> Exactly, without shelter, or somebody who can't come inside, and be sheltered from the cold exposure, those people can also experience hypothermia. When the blood is cool enough to lower the body core temperature significantly into the hypothermic range, do we see any changes in physiologic parameters? Do the vital signs change at all? Ryan, you're saying yes. >> One that we'd see would be a decrease in temperature. >> Well a decrease in temperature, for sure, because that's the definition of hypothermia and then what else might go along with that? >> We may see decreased heart rate. >> Yes, definitely. Anything else? >> Decreased respiration. >> Decreased respiration rate. Um-hm. Can you think of anything else? Well, I can tell you that in a hypothermic condition, we would also start to see a fall in blood pressure because blood pressure mechanisms that regulate blood pressure would start to fail, if the condition was severe enough or prolonged enough and ultimately we would expect if the hypothermia was severe enough a patient would, or a person, would lose consciousness and that would obviously be very detrimental. So hypothermia is a state in which the body cools so much that the normal reflexive mechanisms that help us bring the body temperature back to normal just don't work effectively. Amanda, you maybe see this in a clinical setting. >> Certainly, in a emergency room setting and there are some physiological conditions that can cause the body to not regulate its temperature well enough but we do some interventions to help people rewarm. So Lydia, what's one thing you think we might do to help someone who's hypothermic? >> Well, we'd maybe want to keep the room in which they're staying warmer then to just try and raise their body temperature some. >> Right, we'll raise their body temperature. So keeping the room warm, blankets, hot water bottles, if they're awake warm beverages but would we want to crank the room up to 80? Would we want to rewarm them quickly? >> No, you probably want to do it slowly. >> And Ryan, I saw you shaking your head. So why would we want to rewarm them slowly? >> You don't to have a dramatic increase in temperature. You want the body to gradually increase. >> Okay, to give the body time to recuperate and not to, to shock the system. So, Dr. Scanga also mentioned that low blood pressure can be a consequence of hypothermia. Stacy, what do you think we might do to help offset that in a hypothermic patient? >> Give the patient some fluids. >> Right, some fluids. So if they're awake and alert, give them some oral fluids, something warm to drink and we even give IV solutions that have been warmed, as well. We'll get to you soon, Naomi. >> I would also just, l think like to finish the hypothermia portion of this lecture by saying that we can survive internal body temperature conditions as low as like 22 to 24 degrees C, and then be gradually rewarmed to the normal body temperature range without any permanent damage to organs. And so hypothermia is a treatable condition as long as it's not too severe and the patient has not progressed too far into an imbalance of temperature regulation. Okay. So at the other end of the continuum, we're not too cold, the other end of the continuum is too hot, hyperthermia, and when we think about hyperthermia there are gradations of the condition. The less severe hyperthermic condition is a condition that we commonly call heat exhaustion. If you think for a minute with me about what could be going on during this experience of heat exhaustion, the basic characteristic of the condition is that the person who's experiencing heat exhaustion will have trouble maintaining normal circulatory pressures. So blood will not be able to circulate through the body effectively. What this results from is that the heat loss mechanism that is triggered by the hypothalamus is going to trigger sweating and the sweating is going to result in loss of body fluid, which will then cause a loss of blood volume, which will make it difficult to maintain normal blood pressure and normally, if we think about somebody who was in a thermal neutral environment and they were just maintaining normal body temperature, if that person was experiencing a fall in blood pressure, the compensation that would be triggered would be to vasoconstrict peripheral blood vessels, so we could bring blood back to the body core and help to maintain blood flow to vital organs. But when someone has become hyperthermic, we know that normally what will be part of that increase in body core temperature is vasodilation in the periphery as the way we can lose body heat, right? So conflicting signals, right? We've got so much heat, we want to vasodilate in the periphery, blood pressure has fallen, and you would think that we would vasoconstrict but when heat exhaustion is occurring, the normal mechanisms don't work, and so what happens is the vasodilation is prolonged, and it just kind of worsens that inability to maintain circulatory pressure. This is actually a not uncommon situation that can occur in people who have exercised for a prolonged period of time in a hot environment. It would be very common for them to have been sweating, so that they could cool the body. That sweating results in a loss of body fluids and ultimately, they will be at the point where the loss of body fluids compromises their ability to maintain circulatory pressures. So what kind of what kind of symptoms might a person experience if they were suffering from heat exhaustion? >> Dizziness? >> Yeah. They may, because they're having trouble maintaining proper blood flow to the brain. They can experience some dizziness. Naomi, did you have an idea? >> Shortness of breath? >> Well, maybe we would see that. We, we, most of the effects are initially going to be experienced in the brain. So a person may have, they may get a headache. They may feel a little bit of dizziness. I would expect that they could feel some nausea or some discomfort in their stomach. What are we going to do with someone who's having this experience, Amanda? >> Well, what do you guys think? We're going to want to cool them, cool them down and as Doctor Scanga mentioned heat exhaustion is almost a, a twofold problem. You have the heat, and you have dehydration. So we want to cool these patients down and hydrate them. So if say, you're assisting at a marathon Stacy, and you see someone who's, who's, seems to be in distress with a headache, maybe a little dizzy, what would you, what would you do? Give them some fluids and have them rest. >> Mm-hm. >> For a little bit to not, like, have them move around so they create more heat. >> Have them sit down, give them something cool to drink, sit in the shade, have them rest and Naomi, what are we worried about, what are we trying to prevent with a patient who has heat exhaustion? >> You're trying to prevent them from exerting themselves more and further like, worsening. >> Right, right. >> Their condition. >> Excellent. >> Exactly, because if we don't interrupt the, the process that's going on during heat exhaustion by starting to cool the body, and rehydrating the person, the condition can very quickly progress to the next stage of hyperthermia, that we call heat stroke and that is much more severe. Basically, in heat exhaustion, the body's reflex loops are still working to some degree. They may not be able to correct the imbalance that is occurring but the brain is still functioning enough that the body's heat loss mechanisms are attempting to work. In contrast, in high, in a condition of heat stroke, the hyperthermia is so severe that, the, the brain is no longer able to implement normal feedback loops to try and correct the hyperthermia and in fact, a positive feedback cycle is, is, created, in which the hyperthermia actually generates heat loss mechanisms that worsen the condition, and the worsened condition further exacerbates the mechanisms, and so, very quickly, someone can progress to a very serious condition, if we don't interrupt the hyperthermic process. So one of the first things that we would see is somebody who is experiencing heat exhaustion will be sweating, right? And so their skin will probably feel warm and moist because there will be sweat on the body's surface but when somebody moves into a state of heat stroke the skin will be hot and dry. Can you speculate why? Stacy. >> Is the body starting to try to compensate the fluid loss, so it's going to try to stop sweating so that it doesn't lose anymore? >> Yes. Yes. Yes. So the skin is dry because sweating has shut down and when sweating shuts down, then your chances of having any heat cooling mechanism are pretty poor. If body core temperature goes up too high, again, this is a review but why do we worry if it goes up too high? Lydia? >> Well, when the temperature rises, it just interferes with the functioning of the enzymes, which are necessary for pretty much everything. >> Exactly! They're necessary for everything and so when the body temperature goes too high, what we are going to see is a progressive shut down of various vital organs and somebody who has experiencing heat stroke can have shut down of kidneys, liver, brain, many of the vital organ functions. Are there any conditions, Amanda, that might predispose someone to being prone to having heat stroke? >> Well, older adults don't have as, as sensitive thermoregulation. They can't sense fluid lost, thirst, and heat as well as a younger person. So older adults are at risk for hyperthermia and also very young individuals, neonates, newborns, and young children who also don't regulate fluid well and can't tell you that they're thirsty or they're too hot are also at risk for hyperthemia. >> Did you have others, because I'm also thinking, people with cardiovascular disease. >> Yes. >> Or peripheral vascular disease will also be at risk because they have trouble maintaining blood pressure and cardiac output, when they're in very physiologically stressful kinds of conditions. >> As are pregnant women. >> Mm-hm. >> And others who have say someone who's in chronic kidney failure who has a poor regulation of fluid and I want to emphasize Dr. Scanga that hyperthermia is a medical emergency. >> Mm-hm. >> If you suspect hyperthermia, you need to look for help, call emergency services. >> Mm-hm. Mm-hm. And again the you know, when you do get to the emergency department at a hospital, what will they be doing if you have heat stroke? >> So there will be an emphasis on preventing organ failure. So we do want to cool off the patient but the emphasis would be to take care of those core organs so cool IV fluids, replacing the fluid volume, and there are things like ice packs and cooling blankets, and cooling protocols that are used in hyperthermic situations but it's an emergency situation. >> And so the goal is to cool the body and rehydrate because heat stroke, if it's severe enough, truly can be fatal because of the multiple organ shutdown that's possible.
