What is heat stroke? (Recognize it and guard against it)

A heat wave is coming to France, with temperatures approaching 40°C. The elderly and children can be particularly vulnerable… but it is often forgotten that these heat-related illnesses can occur even in a young, healthy person who is well hydrated. It is enough that the heat is stronger than the body can withstand.

Heat stroke (hyperthermia) occurs when our body's ability to dissipate heat is exceeded and it can no longer cool itself. This may be due to a strenuous exercise such as the high temperature of the environment, being in a hot environment (closed car, etc.)

To counteract overheating, we increase our sweat production and the small blood vessels in our skin dilate to bring the heat to its surface in order to evacuate it. However, a hot and humid atmosphere reduces its effectiveness.

What happens in our body during prolonged exposure to excessively high temperatures?

Here are the stages of this "thermal discomfort" and what amplifies the risk of being the victim. Cramps are the first stage of this process, followed by exhaustion and finally the actual heat stroke.

Multiple levels of risk: mild, moderate, severe

Le heatstroke can be serious and lead to brain damage, coma and death if untreated. It is characterized by a considerable increase in body temperature, which can then rise to more than 40°C.

People with hyperthermia gradually become confused, irritable or even aggressive, have headaches, dizziness and sometimes hallucinations. Their skin is reddened, they feel an intense thirst. They may have difficulty walking, muscle tremors, a pulse over 130 beats per minute, suffer from nausea and breathe faster than normal.

This constellation of symptoms can feel like taking cocaine or a reaction to a drug like aspirin, an infection, or alcohol withdrawal.

Any victim of heatstroke should have their body temperature lowered immediately.

To do this, she must be placed in the shade, stripped naked, and water, preferably warm, can be sprayed on her body with a fan directed at her. Hot water is used to avoid inducing chills, which is a mechanism used by the body to generate heat.

Cooling should be discontinued when body temperature returns to around 39°C to avoid transitioning to a hypothermic state, i.e. when core body temperature becomes too low.

Almost everyone with heat stroke is admitted to hospital to monitor electrolytes in the blood (sodium, potassium, etc.) and their level of hydration, as well as to assess other risks of problems such as organ dysfunction.

Other heat injuries are not as severe. They can, for example, be limited to heat cramps: painful contractions of large muscle groups (legs, stomach, etc.) resulting from the inappropriate practice of intense physical activity in the heat and insufficient hydration. Heat cramps do not affect our mental abilities or cause our temperature to rise too high.

Drinking alcohol, being tired and being sick before exercising increases the risk of experiencing heat cramps and other heat-related side effects.

There is no specific treatment other than rest, get into a cool environment, and return to adequate hydration. If the dehydration was significant, the use of an intravenous infusion can be considered.

Heat exhaustion is a mild condition involving dehydration and minor hyperthermia: the body temperature rises, but then usually remains below 40°C. Those affected may experience nausea, vomiting, dizziness, signs of dehydration – and fatigue, therefore. Brain functions are not affected.

The treatment is the same as for the cramps and the prognosis is excellent, since the main organs are very little affected. It may be preferable to be examined by a doctor, without this necessarily leading to hospitalization.

Our cooling system

Our body works best with a internal temperature of 37°C. To maintain a constant temperature, it uses various homeostatic mechanisms. In case of cold, the shivers thus serve to generate heat.

In case of heat, our body must dissipate it to stay in its optimal operating zone. To cool itself, it uses respiration, conduction, convection, transpiration and evaporation and radiation. Depending on the temperature, the area of ​​the body, whether we exercise or not, the rate of heat evacuated varies a lot.

Conduction involves direct physical contact with cooler objects. An example would be taking a glass of ice water in your hands. But this mechanism is only valid, on average, for 2 to 3% of the heat we lose.

Convection, which accounts for about 10-20% of heat loss, involves the transfer of heat to the air or water around us. Especially when we use a fan to blow in fresh air, take a cold shower, etc.

About 30% of our heat loss comes from evaporation. We do this by sweating, but other animals have different mechanisms: dogs pant, kangaroos lick their forearms, and so on.

Radiation is our most important means of losing heat. It transfers heat from our body in the form of electromagnetic waves and can account for around 40% of heat loss. Unfortunately, as soon as the ambient temperature exceeds 35°C, the radiation loses its effectiveness.

All of these regulatory mechanisms can be influenced by other factors, including humidity, our clothing, our hydration, etc.

Prevent heatstroke

Research has been done on genetic factors that predispose some people to be more vulnerable to heat. Certain medications seem to help prevent these effects in animal testing. But the key to combating the rise in temperature and its consequences is prevention.

Minimize strenuous activities in hot weather, adapt your environment by staying in air-conditioned or well-ventilated buildings, lower blinds and shutters, use fans, stay hydrated, and limit your consumption of alcohol and pharmaceuticals.

Infants, the elderly, and people with chronic illnesses may not be able to modulate their heat exposure as well as others, and should take special precautions.

Athletes must also be aware of the risks they run to practice under these conditions.

Therefore, on hot days, grab a bottle of ice water, head to a cool indoor environment, and go for a quiet activity if you want to avoid falling victim to the heat.

Brian Drummond, Assistant Professor of Emergency Medicine, University of Arizona

This article is republished from The Conversation under Creative Commons license. Read theoriginal article.