It is a hot, humid summer day.
You have gone for a long bike ride, pushing yourself for the final five kilometres to meet your training milestone. Or you have spent much of the day weeding your garden, repeatedly hoeing clods of dirt and bending over to pluck unwanted plants.
Now, you feel dizzy and light-headed. The queasiness in your belly reminds you of being sea sick, and soon your stomach churns. In a few minutes, you may rush to the toilet to vomit.
These are signs that you have heat illness, sometimes called heat exhaustion, a condition that emergency room physician Dr. Eric Letovsky says must be taken seriously.
“There comes a point when your body stops responding appropriately to the heat and you move from heat illness to heat stroke,” says Letovsky, chief of emergency medicine at Trillium Health Partners, which include Credit Valley Hospital, Mississauga Hospital and Queensway Health Centre.
“Your respiratory rate doesn’t go up anymore, your bodily functions stop working … you stop sweating. You actually lose the most basic physiological responses to heat.”
The extreme form of heat illness is known as heat stroke. People experiencing heat stroke will appear confused and disoriented. They may make poor, perhaps life-threatening decisions. Letovsky says people suffering from heat stroke, a potentially fatal medical emergency, must seek help immediately.
“It is a very rare, but real, occurrence,” he says, noting those most at risk are people, such as marathon runners, who overextend themselves with exercise or exertion in extreme heat.
As expected, cases of heat illness increase in the summer. So too, Letovsky says, do the number of people seeking help for dehydration. In some cases, he adds, people have become dehydrated as the result of food poisoning, another health risk that increases as the temperature rises.
Recommendations from an emergency room physician
Employ common sense: Stay out of the heat when temperatures soar over 33C. Minimize exertion. Seek out air conditioning during the hottest parts of the day. Apply sunscreen. Drink a lot of fluid.
“I can’t emphasize the fact that people need to stay hydrated and to stay cool at all costs.”
When to go to the ER
“When people show extreme signs of heat stroke — confusion or disorientation — they must be taken to an emergency department right away,” Letovsky says.
And, when it is hot outside, symptoms of light-headedness, nausea and vomiting could be signs of serious underlying conditions and potential warning symptoms of mild to moderate dehydration. Letovsky says patients should be taken to the ER, where they can be assessed, receive appropriate blood work and, if needed, be “rehydrated aggressively” with intravenous fluids.
Who is at risk
Letovsky says to pay special attention to children and the elderly for signs of heat illness and dehydration.
“It’s really important to keep toddlers out of the sun. They can’t access fluids as frequently and liberally as adults, and they may not ask for fluids while having fun in the heat.”
Hats, he adds, are “just imperative.”
The elderly are also at increased risk, in large part Letovsky says, because they have decreased thirst perception.
Those with limited mobility and people with chronic medical conditions, such as diabetes, heart disease and respiratory illnesses, are also at higher risk. Some medications, including those for high blood pressure, can act as diuretics and cause your body to lose more fluids.
Don’t sweat it
Lawrence Spriet has spent 15 years studying the science of hydration and thermal regulation.
Or, in simple terms, the science of sweat.
The professor and chair of human health and nutritional sciences at the University of Guelph can reel off fact after fact of how the body works to stay cool.
In brief, this is what goes on: As our body takes in heat from external sources — i.e. sunshine — or generates heat during exertion, this heat is transferred from our body’s core, to its periphery, by an increase of blood flow through the skin. Fluid in the blood moves into sweat glands, which then excrete water on to the surface of the skin. “We either lose the heat because the water drips off our body,” Spriet says. “Or, even better, it gets evaporated, causing us to lose more heat.”
It’s a highly efficient cooling system. But, Spriet says, there is one downfall.
“The price we pay is the loss of body water.”
The danger in the body becoming dehydrated is that it loses the ability to dissipate heat, causing an increase in its core temperature. As the body heats up, heat illness can set in, followed by heat stroke, a potentially fatal medical emergency.
Spriet says most of us do replenish lost fluids before the situation becomes dire. But just to be safe, here are some facts and tips, courtesy of Spriet, to keep in mind during the sweltering days of summer.
• The average person doing light exercise loses about half a litre of water per hour.
• During a heat wave, most of us will easily lose half a litre of water just sitting or lying in the sun.
• An elite hockey player loses 1.5 litres per hour during training and play.
• For the average person, doing an average amount of activity, water is enough to rehydrate. Other than water, the two main ingredients in most sport drinks are salt and sugar. Many of us will replenish our salt stores in the snack or meal following activity.
• Our bodies can quickly acclimate to heat. It takes just two or three exercise sessions in higher temperatures for our bodies to increase its blood volume (a person who weighs 70 kilograms will go from about 5 litres of blood to 5.5 litres) to help dissipate heat during exertion.
• Worried about dehydration? Check the colour of your urine. Clear, pale urine means you are hydrated. If your urine is dark in colour, it’s time to drink more fluids.
• A simple way for anyone — whether a backyard gardener or long-distance cyclist — to determine how much fluid they have lost is to hop on the bathroom scale before and after exertion.
Here is how Spriet explains it: “If I normally weigh 70 kilograms, and I’m outside working in the heat, and I come in and weigh 68 kilograms, then I know that I’ve lost 2 kilograms of mostly fluid. Those 2 kilograms are close to 3 per cent of my body mass.” One litre of water weighs approximately one kilogram.