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by Joanne Senn RN, CEN

Heat Exhaustion
H eat Exhaustion and Heat Stroke

     The body's regulatory center (internal thermometer) is the hypothalamus in the brainstem. The increase in blood temperature is sensed and mechanisms are activated for heat dissipation; blood vessels dilate that promotes radiation and convection heat loss. Also, as body temperature rises, mojor heat loss occurs via sweating (evaporation), which is the main mechanism used for cooling. Humans may sweat up to 1.5 Liters/hour, Sweating also leads to loss of potassium and sodium. The body can tolerate up to a 5% loss of body weight in perspiration, but then dehydration occurs after that if replacements aren't adequately made.

     Heat exhaustion or heat stroke occurs when the body is unable to regulate body temperature with normal coping mechanisms. Factors such as drug influence, excessive exercise, high ambient temperatures increase internal heat production.The body is constantly striving to maintain core temperature of 100 degrees F or 37.8 degrees C.

     Elderly people and children are particularly more prone to heat-related emergencies than others. People with psychiatric illnesses are also more prone because they do not sense heat as others do due often to medications or lack of perception.

     Heat exhaustion usually occurs in older adults that have been exposed to heat for several days; perhaps they have no air-conditioning and are exposed to high temperatures.The end result is dehydration and electrolyte imbalance. The symptoms may be stomach cramps, nausea, vomiting, weakness, thirst, headache, leg cramping, confusion. The person usually will need cool fluids orally, intravenous fluids and removal from the stressful environment.

     On the other hand, heat stroke is a serious emergency that occurs when the body's normal thermoregulation fails to reduce temperature.The symptoms of heat stroke are temperature greater than 104 degrees, rapid pulse, low blood pressure, and neurological impairment. Often times sweating is absent and the skin is very hot and dry to touch. This state usually means that there is severe depletion of fluids and electrolytes in the body and require emergent treatment. If untreated, this state can lead to cardiovascular collapse, brain damage and death. There is often a high mortality with HEAT STROKE.

     Call 911 if you suspect someone with heat stroke especially if elderly. Watch out for homeless people on street, psychiatric patients who cannot perceive temperature changes or someone inebriated on the street. If you suspect heat exhaustion in someone, provide them with a cool environment and give cold fluids. Alcohol should be avoided because it causes more dehydration . Cold fluids should be ingested before exercising, during and after. Warm fluids should not be taken because they are warming the body! Children and older adults should avoid extreme heat situations.


Bryant, K. (1994), Emergency Nursing Core Curriculum, 4th ed. , Philadelphia: Saunders.

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