Summer Heat Can Kill

Q:  With the summer heat upon us, I was wondering, how is it that people actually die of the heat? Is it really just dehydration or is it an actual stroke?

A:  Normally, the body keeps cool by evaporation, radiation, conduction, or convection. Evaporation, the principal cooling mechanism, occurs when sweat dissipates into the air - basically, it's a liquid turning into a gas. This process is sped up by heat, but it also depends on the relative humidity. When it's humid, sweat evaporates more slowly because the air already contains so much moisture.

Radiation, conduction, and convection operate by transferring heat to the ambient air. These cooling mechanisms only work if the air temperature is cooler than the body, that is, cooler than 98.6° Fahrenheit (F) or if the body is placed next to a cooler object like a swimming pool filled with water.

The normal cooling mechanisms don't work as well in persons who are very young or of advanced age, or who have heart disease or other chronic health problems. They depend on an accurate nervous system to set the body on alert by increasing sweating and on a well-functioning circulatory system to send the water to the skin.

People suffer heat-related illness when the body's temperature control system is overloaded.

Heat stroke is the most serious heat-related illness. It occurs when the body becomes unable to control its temperature: the body's temperature rises rapidly, the sweating mechanism fails, and the body is unable to cool down. Body temperature may rise to 106° F or higher within 10 to 15 minutes.

When the body's temperature is extremely hot, hotter than 108° F, cells in the body lose the ability to create ATP (adenosine triphosphate), the source of energy for the cells' machinery. Also, enzymes - proteins made in the body to help process food and toxins - cease to function. As a result, many organs and organ systems will not work well (the lungs, nerves and brain, blood vessels, and the liver, among others).

"Heat stroke" is nothing like what we usually think of as a "stroke," where a blood clot or bleeding artery in the brain causes numbness or weakness on one side of the body. But heat stroke can cause death or permanent disability if emergency treatment is not provided.

The Centers for Disease Control and Prevention (CDC) has several recommendations to prevent heat stroke: take a cool shower or bath, drink fluids to replace evaporated sweat, limit exercise, and get into an air conditioned area. Make sure your drinks are non-alcoholic and without caffeine. If you are on a fluid-restricted diet, talk with your doctor about how to stay hydrated.

Warning signs of heat stroke vary but can include the following:

• An extremely high body temperature (above 103°F)
• Red, hot, and dry skin (no sweating)
• Rapid, strong pulse
• Throbbing headache
• Dizziness
• Nausea
• Confusion
• Unconsciousness

If you see a person showing any of these signs, you could be dealing with a life-threatening emergency. Have someone call for immediate medical assistance while you begin cooling the victim. Do the following:

• Get the victim to a shady area.
• Cool the victim rapidly, using whatever methods you can. For example, immerse the victim in a tub of cool water; place the person in a cool shower; spray the victim with cool water from a garden hose; sponge the person with cool water; or if the humidity is low, wrap the victim in a cool, wet sheet and fan him or her vigorously.
• Monitor body temperature and continue cooling efforts until the body temperature drops to 101°-102°F.
• If emergency medical personnel are delayed, call the hospital emergency room for further instructions.
• Do not give the victim alcohol to drink.
• Get medical assistance as soon as possible.

Most heat disorders occur because the victim has been overexposed to heat or has over-exercised for his or her age and physical condition. Remember that older adults, young children, and those who are sick or overweight are more likely to succumb to extreme heat. Make sure you know your limits, and watch for signs of heat illness in yourself and others.

Julie L. Mitchell, MD, MS, is an Assistant Professor of Medicine at the Medical College of Wisconsin. She practices at the Froedtert & The Medical College of Wisconsin General Internal Medicine Clinic - East. Her column appears in the Milwaukee Journal-Sentinel.