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It’s hot outside? Beware of heatstroke!

Published on October 21, 2017 at 14:41 / Updated on May 6, 2022 at 17:52

It’s a nice July day and you decide to enjoy the sun on your patio with your one-year old son. The sun is shining and there is not a single cloud in the sky. This is truly a magnificent day. You’ve been enjoying the sun for a couple of hours when you notice your son is clearly not feeling well. Fever, nausea, dry and hot skin: he looks bad. What’s happening to him? He could be suffering from heatstroke brought about by overexposure to the sun. When it’s hot outside, you have to remember that the sun can be dangerous and you need to take this danger seriously.

He could be suffering from heatstroke brought about by overexposure to the sun. When it’s hot outside, you have to remember that the sun can be dangerous and you need to take this danger seriously.

What is heatstroke?

Heatstroke is one of the most serious dangers we can face when it’s hot outside. It can occur following exposure to intense heat when the person is not sufficiently hydrated. In fact, dehydration plays a major role in heatstroke. The body needs to have access to a certain amount of internal fluid to maintain its various vital functions, such as blood pressure.

When it’s hot outside, the body sweats a lot. Sweating serves to efficiently maintain thermoregulation processes, which are responsible for keeping the body’s core temperature at an acceptable level. Even though sweating is essential, it causes the body to loose a fair amount of fluid. This fluid loss is without consequence if you drink sufficiently to compensate it. The body still has access to enough fluid to maintain vital function and sweating, allowing the core temperature to remain stable.

If you do not drink enough liquid to compensate for sweating, you will be more at risk of heatstroke when it’s hot. During hot days, the body will not have access to enough fluids to maintain both vital functions and core temperature. It will then redirect fluids to maintain vital function and will stop sweating to cut fluid loss. As a result, it will no longer be able to maintain its core temperature at an acceptable level. After a while under such conditions, the core temperature will rise sharply and the person will feel unwell.

Heatstroke is defined as the elevation of the body’s core temperature above 40 C due to failure of the thermoregulation processes. There are two types of heatstroke: exertional and non-exertional. Non-exertional (or classic) heatstroke occurs on extremely hot days, without any physical effort. The elderly and young children are especially at risk.

Exertional heatstroke occurs following intense and prolonged physical effort. Athletes and those who work outside are most at risk of exertional heatstroke if they do not drink enough liquids to compensate for losses due to sweating.

Other risk factors also increase your risk of heatstroke on hot days: obesity, alcoholism, Parkinson’s disease, being older, uncontrolled diabetes, being frail as well as taking certain drugs, such as diuretics and antihistamines. Wearing clothes that keep you hot as well as suffering from certain skin diseases could also precipitate this illness. Finally, those who have to work outside during very warm spells are especially at risk. Certain work conditions can also increase the risk of heatstroke, such as a rapid pace of work, no nearby source of water, wearing clothes that keep the heat, etc.

What are the signs of heatstroke?

Warning signs of heatstroke vary from one person to another. In 20% of cases, the person may experience minor clinical signs such as muscle cramps, fatigue, intense thirst and nausea. At this stage, moving the person out of the hot environment and giving him fluids can be enough to correct the situation.

When heatstroke occurs, a number of signs and symptoms will appear, usually fairly quickly. In all cases, the core temperature will rise above 40 C. It can be associated with several manifestations such as rapid pulse, low blood pressure, dry, red and hot skin, severe headaches, nausea and vomiting. In more severe cases, the person can lose consciousness (which could lead to coma), and experience delirium, strange behaviour or seizures.

You should be able to distinguish between heatstroke and other heat-related illnesses. For example, in heat exhaustion, moderate fever is present while in heat cramps or sunburns there is no fever. The intensity of the fever is thus used to distinguish between heatstroke and other heat-related disorders.

These other heat-related disorders are still very serious and should be treated appropriately, but they are usually benign and not considered medical emergencies, contrary to heatstroke.

Among other heat-related disorders, heat exhaustion is the one most similar to heatstroke. Heat exhaustion is a progressive condition that usually occurs in people who are dehydrated while in a hot environment. If it’s not properly treated, heat exhaustion can lead to heatstroke. Those who suffer from heat exhaustion are still able to somewhat regulate their core temperature. They usually present with profuse sweating and cold, pale and moist skin. They can also experience other symptoms such as weakness, nausea, dizziness, and headaches.

The core temperature is usually moderately high, not exceeding 38,5 degrees Celsius. Fever and sweating as well as skin color can help distinguish between heat exhaustion and heatstroke, which is important to determine what measures need to be implemented. The measures are quite similar, but heatstroke commands more urgent medical attention than heat exhaustion.

What should you do?

Heatstroke is a medical emergency that requires medical attention as soon as possible. Inappropriate management or delay in seeking medical attention can have severe, even fatal, consequences. Consequently, you should first call emergency services to ensure the victim will be transported to a hospital. It is essential that the victim be seen by a physician as soon as possible to obtain the best possible care. While waiting for medical help, the victim should be moved to a fresh, shaded and well-ventilated location. Loosen the victim’s clothes to help breathing, place him in a comfortable position or create ventilation to help improve his global comfort.

You should then try to cool the victim’s temperature and give him fluids. Several measures can be used to reduce the victim’s core temperature You can splash him with cold water, spray a fine mist on his skin, place ice cubes on his groin, armpits and neck, cover his body with a moisten sheet, etc.

Be sure to use cold water, so as to reduce the core temperature, but not icy cold, which could cause a thermal shock. If the victim is conscious, have him drink some water. If he is unconscious, or semi-conscious, place him on his side while you wait for medical help. You should also check his vital signs regularly (breathing and pulse).

How can you prevent heatstroke?

Several measures can help prevent heatstroke. Most measures are simply common sense and are aimed at avoiding overexposure to the sun as well as dehydration.

To prevent non-exertional heatstroke, which affects mostly the elderly and young children, first limit exposure to the sun, especially when the sun is at its hottest between lunch and 3 pm. If you have to be in the sun, wear pale-colored, loose and light clothing, cover your head with a hat and wear a sunscreen appropriate for your skin type. Never leave a baby in a car parked in the sun, even for a few minutes (even if the windows are opened) and never allow children to play in poorly ventilated and overheated areas. Those most at risk (babies, pregnant women and frail individuals) should be especially wary of the sun and be extremely cautious in times of hot weather.

It is also possible to prevent exertional heatstroke, which affects mostly outside workers and athletes. When possible, those who know they will have to do an intense physical effort in hot weather should progressively train in the two to three weeks prior to the expected effort, in order to get used to the heat. These people should wear light and ventilated clothing, drink enough fluid during and after the activity and respect their personal limits.

These are crucial measures that should be implemented. We know that workers who work long hours under the sun under often difficult conditions are more at risk. The CSST (Quebec Workmen's Compensation Commission) publishes a very complete document to help these workers assess their risk level and teach them measures to prevent heatstroke. You can find this document (in French) at:

Adequate fluid intake is a central measure in preventing exertional and non-exertional heatstroke. You need to drink sufficient amounts of liquid without waiting to feel thirsty, as thirst is a late indicator of dehydration. As a general rule, you should drink one glass of liquid (200-250 mL) every 30 minutes. Those engaging in a physical activity or who sweat a lot may need more fluids. These people should drink 500 to 1500 mL of liquid during the three hours prior to the activity and take 200 to 250 mL every 20 minutes during the activity.

Because fluid loss continues even after the activity, it is recommended to replenish every kilogram of weight lost with four litres of water, to be taken over three hours after the activity. Cold (but not icy) water is a good choice, but so are fruit juices and rehydration drinks such as Gatorade® or Powerade®. These specialized drinks provide electrolytes and are specifically formulated to promote rehydration. In addition, you should avoid alcoholic beverages as well as coffee and tea, since these drinks increase fluid loss.

When the weather is hot, you should always have a supply of water on hand. Those who keep well hydrated are far less at risk of heatstroke than those who do not.

Heatstroke should not be underestimated. It constitutes a medical emergency that must be treated as soon as possible. Various symptoms can help identify heatstroke: core temperature above 40 degrees Celsius, rapid pulse, dry, hot and red skin, severe headaches, nausea and vomiting. Young children, the elderly and workers that work outside are usually most at risk. Fortunately, heatstroke can be prevented through simple measures. This summer, enjoy the sun reasonably and don’t forget to drink plenty of liquids!

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