By John Messmer
Penn State Family and Community Medicine
Penn State Milton S. Hershey Medical Center
Penn State College of Medicine
It's another hot one in much of the country. Global warming not withstanding, we have experienced one hot summer after another for the last decade. Heat-stress injuries are becoming potential risks even for our Canadian neighbors.
Heat-stress injury is related to excess water loss. Our bodies eliminate heat primarily through sweating. Heat is produced by muscle activity and converting food into energy but is also absorbed from sunlight on skin and darker clothing.
Our brains regulate body temperature by turning on perspiration and dilating blood vessels in our skin to radiate heat away. If sweat cannot evaporate, such as on humid days or when wearing tight clothing, we do not cool off as well. High humidity raises the heat index, which is like the wind chill factor for cold days. At higher humidity, the body feels and acts as though the temperature is higher. At 90 degrees and 70 percent humidity, it feels like 105 degrees.
By failing to stay properly hydrated, people impair the ability to perspire and cool off. Before heading out for the day's activities, plan to have enough to drink and remember, staying cool is more important than looking cool. It's best to wear light-colored, loosely fitting clothing, which allows air to circulate.
Heavy activities such as sports or yard work require more liquid. Drink one to two cups of water before heading out and another two to four cups of water per hour of activities depending on the heat. Most people should not need more than four cups per hour, even in high heat. Fluid replacement is sufficient if one is perspiring and needs to urinate every three hours or so. Alcohol and caffeinated beverages increase the risk of heat stress by increasing water loss. Many over-the-counter medications such as decongestants, weight-loss products and ephedra also reduce sweating and increase the risk of heat stress.
Timing is another important factor in beating the heat. Exercise or do heavy work early or late in the day when it's cooler. For those just starting an exercise program, go slowly and rest often for the first two weeks while the body learns to tolerate the heat.
Sports drinks are not necessary for the average person. A regular diet and water are fine for all but the elite athlete or for those in desert environments. Salt tablets are dangerous and not recommended. For the average person simply trying to stay hydrated in hot weather, normal kidneys retain all the salt one needs.
Early detection and treatment are keys in battling heat-related injury. The first signs of trouble are usually leg and abdominal muscle cramps, often accompanied by weakness. If this happens, get to a cool place -- inside or in shade -- and drink cool liquids. Do not return to the heat until fully recovered.
Heat exhaustion is the second stage. Low fever develops, and the person is dehydrated, weak and sometimes confused, nauseous and anxious. When this situation occurs, it's vital to get the person to a cool area, preferably indoors in air-conditioning. Keep the skin moist and run a fan to aid evaporation or apply cold towels and offer cold liquids. If recovery does not begin in an hour or if the person is confused or lethargic, call 9-1-1.
Heat stroke is the final and potentially fatal stage. About 400 people die annually from heat-stress injuries. Body temperature is high, as much as 104 degrees, and typically the skin is hot and dry. Although sweating usually stops at this point, the person may have slightly damp skin. The victim often is delirious or even unconscious because he or she is in shock and requires emergency treatment. Call 9-1-1, then apply ice packs to the victim's armpits and groin, because cooling the body is critical. Offer fluids only if the person is awake. Intravenous fluid usually is needed.
Several special cases bear mentioning. Children do not lose heat as effectively as adults and are more susceptible to heat injury at temperatures when healthy adults may be fine. Older people may not feel the heat as well and do not sweat as efficiently as younger people. This combined with medical problems and medications that can affect sweating are the reason more than half of all heat-related deaths occur in this age group. Alcohol abuse, sunburn, eating disorders, fatigue, obesity, thyroid disease, uncontrolled diabetes and upper respiratory infections all increase the risk of developing a heat-related illness.
With simple precautions summer can be safe. For detailed information on the heat including a heat index chart, visit http://www.crh.noaa.gov/pub/heat.php online.