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Heat Exhaustion or Heat Stroke -
Which Is Worse?

By Dr. Peter W. Kujtan, B.Sc., M.D., Ph.D.

Dr. Peter W. Kujtan

Heat exhaustion is the predecessor to heat stroke. We spend all spring waiting for the heat, and often underestimate heat wave problems. Heat illnesses account for thousands of emergency visits yearly. Most of us have experienced mild Heat Cramps, those painful leg cramps that sometimes occur while exercising in the heat. No need for salt tablets, simply replenish your water, rest and they resolve.

Our bodies dissipate heat in many ways, but mostly by sweating and radiating it out. When we are active in hot or humid environments, controlling body temperature is more difficult. Our core temperatures begin to rise, but stay under 41°C. Our pulse increases; we sweat profusely, breathe faster and begin to feel weak and achy. Exertion in hot weather can produce 2 liters of sweat per hour. Drinking 300 - 500 ml of water prior to exercise is a must, along with regular water during activity. Salt tablets can produce sodium overload and need only to be used by elite athletes under physician direction. Beer and alcohol have no role in treatment, and should be avoided.

Heat exhaustion leads to Heat Stroke which is a medical emergency requiring hospitalization. It can develop more suddenly than people expect. In the 1995 Chicago heat wave, almost five hundred people died of Heat Stroke. When the humidex is above body temperature, our only means of cooling is sweating. Radiated cooling depends on heat moving from our bodies to the cooler air. When the air is warmer than our bodies, heat actually moves into the body. Sweating eventually fails to regulate heat and our core temperatures rise above 42°C, a fatal trend. Sweating eventually stops, our skin gets hot and dry, we become nauseated, develop respiratory distress, headaches, and may begin to hallucinate or behave bizarrely. The elevated temperature will cause kidney failure, seizures, and brain swelling and general organ failure. Immediate first aid should aim at cooling the victim, and immediate removal to a hospital. Delays of more than 90 minutes are associated with a poor prognosis and death. Heat Stroke is best defined by temperature.

Prevention is the best solution. All kids' activity should cease anytime the humidex is above 35°C. Wear light clothing, stay in the shade and drink lots of water. Expensive store bought fluids offer very little advantage to the average person.

Related resources:

Staying Cool in Extreme Heat. Video from FEMA, 0:55 min.

Heat Stroke from MedicineNet.com. Understand the Risks and Signs of Dehydration by Melissa Conrad Stöppler, MD.

Heat stress - preventing heat stroke from Better Health.vic.gov.au.

Heat Exhaustion: Prevention from Mayo Clinic.

Heat Stroke: Prevention from Mayo Clinic.

Tips for Preventing Heat-Related Illness from Centers for Disease Control and Prevention (CDC).

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