Aging Begins at 30

Killing Heat

Ian Maclean Smith, M.D.
Emeritus Professor
Department of Internal Medicine
University of Iowa Hospitals and Clinics
Creation Date: July 2002
Last Revision Date: July 2002
Peer Review Status: Internally Peer Reviewed

Our son, who cycles long distances, asked, "What is heat stroke?" This was after a trip of over 50 miles in 108-degree F (heat index) weather. Damaging (apparent) heat is measured by the heat index, a combination of heat and humidity. A heat wave is defined as three or more consecutive days of air temperature over 90 degrees F (>32.2C).

Related diseases that overlap are heat cramps, heat exhaustion, exertional heat injury (typically suffered by soldiers, long distance cyclists, and marathon runners), and heat stroke. U.S. heat-related disease deaths yearly average 380 but vary from 150 to 1,700.

Heat stroke is a medical emergency with body temperature rapidly rising to over 105 degrees F (>40.6 C) with lethargy, disorientation and then delirium and coma. The skin is hot and dry. Temperature lowering with salt and fluid replacement is urgently needed. Survival depends on prompt diagnosis and treatment but is often fatal despite iced baths because there is already brain damage. Heat exhaustion is milder with dizziness, weakness and fatigue. Physical exertion during hot weather can cause heat syncope (fainting).

The elderly with chronic heart disease, lung disease, mental disease or Parkinson's disease are mainly affected. Other factors are social isolation, alcohol, anti-depression medicines, antihistamines, cough medicines, and other over-the-counter medicines. Salt tablets are not helpful and may be dangerous. Nonwhite races are five times more often affected than white.

In very hot weather, fans are not protective but air conditioning is and should be sought even for short periods in malls, senior centers and public libraries. Neighbors, relatives and letter carriers are useful in finding those elderly who are at risk.

The elderly in certain large cities (Chicago, St. Louis and Memphis) are particularly likely to be affected. City contingency plans should be in place. Targeted action can save lives by listing elderly people at risk because of disease, immobility or prior heat related trouble. Excess deaths do not usually occur until the second day of the heat wave. Then media warnings, especially on the TV (the only connection with the world for many elderly) should be broadcast with urgent instructions about the use of any available air conditioning. Some cities have in their building codes the need for air conditioning in lobbies of all hotels and large apartment buildings.

If one analyzes the risk of death in persons with a characteristic compared to those without it and call it an "odds ratio" then the problem areas are, confined to bed (odds ratio of x 8), do not leave home each day (x 7), live on the top floor of their building (x 5), live alone (x 2). Benefits are gained from functioning air conditioners (odds ratio of x 0.3), and access to transportation (x 0.3). Elderly persons dead of heart disease during a heat wave have similar risk factors and may have died of heat or heart problems or both. The obese are not unusually susceptible.

I told our son, "Duck into any air conditioned store, even for only half an hour" when taking your annual 500-mile ride across Iowa, "and survive in good health!" Prevention is the key word!

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See related Patient Topics Heat Illness, Injuries and Wounds or Symptoms and Manifestations.

See related Provider Topics Heat Illness, Injuries and Wounds or Symptoms and Manifestations.

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