Dear Doctor Column, August 21, 2006

Avoiding Heat-related Illness

What are the symptoms of heat exhaustion, and how can I avoid it?

Answer:

With temperatures setting record highs this summer, everyone needs to take measures to stay cool and avoid overheating. It’s important to learn the signs of heat illness and what to do when they occur, especially if you exercise or work outdoors.

Infants and people older than 65 years are at special risk for heat-related problems as are those with heart problems, high blood pressure, diabetes, obesity, infections, diarrhea, or severe sunburns, which interfere with the body’s ability to sweat. In addition, certain medications increase the risk of heat problems.

Hyperthermia is the umbrella term for a variety of illnesses caused by overexposure to heat, including heat exhaustion, heat-related muscle cramps, or the most serious problem, heat stroke. The body can adapt, within limits, to high environmental temperatures to keep internal body temperature within a narrow normal range. Once the brain senses body temperature is rising, either because of the weather or an illness, it increases the flow of blood to the skin, which increases sweating. Evaporation of sweat cools the skin and the blood flowing just beneath it, which then cools internal organs.

Obviously, you sweat more when it is hot. In fact, while just taking it easy in the heat, you can lose up to 2 quarts of water a day through sweat. High outdoor temperatures and exertion or exercise in the heat can increase the loss of fluid through sweat to 5 to 10 quarts of water a day. You must replace lost fluid for your body to function normally and continue to control its internal temperature.

In addition to environmental temperature, humidity contributes to heat illness. As humidity rises, evaporation of sweat slows and sweating becomes less efficient, increasing the risk of problems. Hyperthermia is most likely to develop when the humidity is high and temperatures are 90° Fahrenheit or above for 3 or more consecutive days — the official definition of a heat wave.

Humidity raises the apparent temperature, or how warm you feel based on the interaction between the humidity and the air temperature. Meteorologists have devised a system, known as the Heat Index (HI), to help measure this effect. For example, if the temperature is 95° and the humidity is 60%, the HI is 114° — that is how hot it feels.

Heat cramps are painful muscle spasms that occur when muscles are deprived of salt, which is often lost through excessive sweating. Heat cramps typically occur in the stomach, arms, or legs. Left untreated, these cramps can develop into a more serious heat-related illness. Take the following first-aid steps to combat heat cramps:

• Find a cool place and sit quietly.
• Drink clear juice, an electrolyte-filled sports beverage, or a large glass of water mixed with a teaspoon of salt.
• Get medical attention if heat cramps do not go away within 1 hour, or if you are on a low-sodium or fluid-restricted diet, or if you have heart problems.

Heat exhaustion can happen after being exposed to high temperatures and not drinking enough fluids. It may occur suddenly or develop after several days of continued heat exposure. It can feel a bit like the flu with symptoms that include irritability, headache, fatigue and weakness, nausea or vomiting, heavy sweating, and intense thirst. If you experience any of these symptoms:

• Get out of the heat immediately, preferably into an air-conditioned area.
• Remove unnecessary clothing.
• Apply water or cold wet towels to the skin.
• Drink cool water or sports drinks. Generally, people with heat exhaustion do not need extra salt.

Signs that heat exhaustion is serious enough to warrant medical attention include cold, clammy skin, a body temperature above 103° Fahrenheit, and no improvement with self-care measures. Untreated, heat exhaustion can progress to heat stroke, the deadliest form of heat illness.

Heat stroke results when the body’s cooling mechanisms break down completely. It is more likely to occur in the elderly and those unaccustomed to high heat and humidity. If someone exhibits any of these signs, seek immediate, emergency medical attention:

• Mental confusion, disorientation, and collapse or loss of consciousness
• Enlarged pupils
• Red, hot, dry skin
• Extremely high body temperature

Heat stroke is a major medical emergency and demands immediate emergency treatment if the victim is to survive. Death will result if treatment is delayed. Call 911 if you suspect someone is suffering from heat stroke and apply cool compresses or ice packs until help arrives.

Remember heat illnesses are preventable, and that it is important to take precautions before you feel too hot. UAB safety experts offer these suggestions to prevent heat-related illnesses:

1. Drink plenty of water to stay hydrated during hot weather, whether you feel thirsty or not. Avoid alcoholic, caffeinated, and sugary beverages, which increase urination, thereby contributing to dehydration.

2. Build up your tolerance to the heat by gradually increasing the time you spend in the heat over 1 to 2 weeks. Your body will increase its ability to adapt to high environmental temperatures.

3. Wear light-colored clothing to reflect heat and sunlight and loose-fitting lightweight clothes made of natural fibers. When you are in the sun, wear a hat, but be sure that it allows air circulation.

4. Stay out of the midday sun, when possible. Avoid strong, hot, dry winds. Seek air-conditioned spaces, even if only for a few hours.

5. Do not rely on fans. If the temperature is above 90°, fans alone often cannot protect against heat-related illness. This is especially true when high humidity interferes with the ability to sweat.

6. Take it easy. During hot weather, exercise in an air-conditioned room or gym, or if you must exercise outdoors, try exercising early in the morning or do aquatic exercises in the pool. Rest at the first sign of fatigue, lightheadedness, or feeling hot. During heat waves, skip any strenuous outside activity.

7. Take baths and showers. Because water conducts heat away from the body, baths and showers in tepid water are good cooling techniques.

8. Eat light. Choose foods high in water content, such as fruits, salads, and soups. Cut down your intake of proteins and fats, which increase the body’s heat production.

If you are taking medications, ask your doctor if any are likely to cause a problem for you when you are in the heat. Diuretics used to treat high blood pressure, for example, can make dehydration worse. Certain other blood pressure and heart medicines can interfere with the body’s ability to sweat, and some tranquilizers dull your sense of thirst.