Thermoregulation : Nursing

Definitions & Key takeaways

Thermoregulation is the body's ability to balance between heat gain and heat loss. This is possible by four mechanisms, called neural and vascular control; heat production; heat loss; and behavioral control. Disrupted thermoregulation can manifest as hyperthermia or hypothermia. Causes of hyperthermia include heat stroke, exercise, hyperthyroidism, and infections, whereas causes of hypothermia include frostbite, diabetes, hypothyroidism, and malnutrition.

The most common cause of hyperthermia is extremely high environmental temperature. In this situation, even though the hypothalamus activates sweating and causes dilatation of superficial arteries, these mechanisms are insufficient to dissipate heat. On the other hand, the most common cause of hypothermia is extremely low environmental temperature. In this case, the hypothalamus activates shivering and causes constriction of superficial arteries, but yet again, these mechanisms are insufficient. Complications of hyperthermia include hypotension, tachycardia, and rhabdomyolysis, whereas complications of hypothermia include electrolyte imbalances, coagulopathy, and arrhythmia.

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Introduction0:00–0:41

Thermoregulation is the body’s ability to balance between heat gain and heat loss, thus maintaining a stable internal temperature of around 36 to 37.5° C or 96.8 to 99.5° F.
This range is considered normal body temperature but it’s actually the average across the population. Normal body temperature can vary depending on the time of day, age of the individual, activity level, and many other factors.
This normal body temperature is maintained by four mechanisms: neural and vascular control; heat production; heat loss; and behavioral control.
Okay, let’s discuss the physiology of these four mechanisms, starting with neural and vascular control. If we zoom into the brain, there's a region called hypothalamus.

Physiology0:41–4:05

The hypothalamus acts like a thermometer. It has thermoreceptors that monitor the body’s internal, or core, temperature; and it also receives information about the peripheral temperature from the thermoreceptors in the skin.
Now, the hypothalamus is also the body’s thermostat, because it controls the internal temperature “set point” and when the core temperature deviates from the set point, the hypothalamus will signal the rest of the body to increase or decrease the body temperature and bring it back to the set point.
So, on a hot summer day, the hypothalamus senses the core body temperature is getting too high and responds by initiating mechanisms like sweating and dilating skin blood vessels, resulting in body heat loss.
On the flip side, on a cold winter day, the hypothalamus senses that the core body temperature is getting too low, and in turn, activates mechanisms like shivering which generates heat, and vasoconstriction in the skin that prevents heat loss.
Now normally the set point is 36 to 37.5° C or 96.8 to 99.5 °F; however, when the person has a fever, the hypothalamus can adjust the thermostat, raising the set point to a higher temperature.
The body responds by increasing the core temperature to the new set point, which is helpful for fighting off infections.
The next mechanism is heat production, which is a result of internal metabolic processes that produce heat as a byproduct.
All tissues in the body produce heat, but a major source of heat production comes from the muscles through voluntary movements like exercising, and involuntary movements like shivering.
In neonates, heat production can happen without muscle activity, called non-shivering thermogenesis. This is because they have a higher percentage of “brown fat” than adults, which is more effective at generating heat.
Next up is heat loss, which is mostly a function of the skin that can happen in four ways: radiation, conduction, convection, and evaporation.
Most body heat is lost through radiation which is the emission of body heat and the transfer of that heat to another object without touching.
Heat generated deep inside the body is carried by blood to the peripheral vessels close to the skin where it can leave the body via radiation.
So the body is constantly giving off heat like a radiator. When the peripheral vessels dilate and there’s more blood flow, more heat is lost.
When these vessels constrict, there’s less blood flow and less heat is lost. Conduction is the transfer of body heat to another object by touching it.
For example, a person with a fever may use an ice pack which absorbs some of the body heat and cools their forehead. Convection is losing heat when air or water movement carries the heat away, so think of using a fan to cool down during a hot summer day.
Last but not least is evaporation, which is losing heat by converting fluid into gas. This is most commonly seen in sweating where the sweat on your skin evaporates from body heat, taking that heat away.
When it comes to behavioral control, this is as simple as moving to a colder or warmer environment or adding or removing clothing.
However, this mechanism depends on factors like the availability of shelter and clothing, and the ability of the person to perform the necessary action.
Now, when the body’s thermoregulatory mechanisms can no longer keep the internal body temperature stable, it’s called hyperthermia if the body temperature is too high and hypothermia if the body temperature is too low.

Pathology4:05–7:44

So, hyperthermia is when body temperature reaches above 36 to 37.5°C. It’s most commonly caused by extremely high environmental temperature, which decreases the body’s effectiveness in getting rid of body heat generated from metabolic processes.
This is especially dangerous if combined with other factors that increase heat generation like exercise or increased metabolism from hyperthyroidism, infections, and serotonin syndrome.
Additional causes of hyperthermia include anything that causes neurological damage such as trauma to the brain or spinal cord.
One thing to keep in mind is that hyperthermia is different from a fever. During a fever, the hypothalamus sets the thermostat to above normal body temperature.
With hyperthermia, the thermostat is still set to normal body temperature, but the body cannot dissipate enough heat to maintain it.
Now, hyperthermia can initially cause heat exhaustion where symptoms include weakness, profuse sweating, and hypotension due to vasodilation as the body tries to get rid of as much heat as possible.
If these regulatory mechanisms eventually fail, there’s a decrease in sweat production, and the skin becomes dry and hot.
The person might become dizzy due to hypotension and the heart rate increases to compensate. They might also experience nausea and vomiting.
Finally, significantly elevated body temperature, over 40.5 C or 105 F, can cause heat stroke. This is where proteins and enzymes in the body stop working or even break down causing organ damage and CNS symptoms like confusion, delirium, coma and eventually death.
The treatment of heat stroke and severe hyperthermia is rapid cooling. The quickest way is to submerge the client in ice cold water, but a less uncomfortable approach is to mist the client’s entire body with lukewarm water and fan them while monitoring body temperature.
On the other hand, hypothermia is when the body temperature dips below 35° C or 95° F. It’s typically caused by the extremely low environmental temperatures.
Both cold air and cold water can carry away large amounts of body heat through conduction and convection, and hypothermia occurs when the body cannot generate enough heat to compensate.
Common risk factors include conditions that decrease metabolism like diabetes, hypopituitarism, hypothyroidism, and hypoadrenalism, or low levels of adrenal hormones; taking certain medications like ethanol, phenothiazines, sedative-hypnotics; conditions that impair the skin such as extensive burns or severe psoriasis; and by trauma or damage to the brain or spinal cord.
In the early stages of hypothermia, the body shivers to generate heat. It will also try to increase other metabolic processes by releasing thyroid hormone, increasing heart rate, and respirations.
There’s vasoconstriction in the skin to decrease blood flow to the peripheral parts of the body and prevent heat loss. When the temperature is extremely cold, frostbite occurs when the skin and underlying tissue freeze, causing permanent damage.
Now, if the core body temperature decreases further despite thermoregulation mechanisms, metabolic processes slow down, leading to bradycardia, hypotension, decreased neural activity, and eventually coma and death.
Alright, as a quick recap, thermoregulation is the body’s ability to balance between heat gain and heat loss. This is possible by four mechanisms, called neural and vascular control; heat production; heat loss; and behavioral control.

Review7:44–8:56

Disrupted thermoregulation can manifest as hyperthermia or hypothermia. Causes of hyperthermia include heat stroke, exercise, hyperthyroidism, and infections, whereas causes of hypothermia include frostbite, diabetes, hypothyroidism, and malnutrition.
The most common cause of hyperthermia is extremely high environmental temperature. In this situation, even though the hypothalamus activates sweating and causes dilatation of superficial arteries, these mechanisms are insufficient to dissipate heat.
On the other hand, the most common cause of hypothermia is extremely low environmental temperature. In this case, the hypothalamus activates shivering and causes constriction of superficial arteries, but yet again, these mechanisms are insufficient.
Complications of hyperthermia include hypotension, tachycardia, and rhabdomyolysis, whereas complications of hypothermia include electrolyte imbalances,