External Heat Illness Guidelines

Body temperature is dependent on a balance between heat production and heat loss. There are several mechanisms by which we lose heat; for example, sweating allows us to lose heat via evaporation (accounts for 20-25% of heat loss). Radiation, convection, and conduction (2% of heat loss) also play important roles in heat loss. Radiation accounts for as much as 70% of heat loss under normal conditions. Hypothermia results when the body loses more heat than it produces.

Temperature regulation is mediated by the nervous system through changes in muscular activity and metabolism. Heat is generated in the body through metabolism and muscular activity. A complex regulating system is responsible for controlling the delicate balance between heat production and loss. When conditions in the environment become too hot or humid and the body is unable to compensate, we become susceptible to heat illness. Certain drugs contribute to the development of heat illness : phenothiazines (chlorpromazine), antihistamines, beta-blockers, diuretics, over-the-counter medications for colds or allergies, and tricyclic antidepressants (amitriptyline, imipramine).

There are 3 types of heat illness:



Heat cramps are usually associated with strenuous physical activity. They occur due to profuse sweating, resulting from a loss of body salt (sodium). These patients are NOT dehydrated. SYMPTOMS are painful spasms of muscles in the extremities and the abdomen. The patient has a normal body temperature, but has not adequately maintained their salt levels because of sweating. Oral fluids and electrolyte replacement will be sufficient. Popular sports drinks, (i.e. Gatorade) are effective in restoring body fluids and salt balance. Persistent symptoms, despite oral intake, require physician evaluation to exclude a more serious heat illness.


Heat exhaustion is similar to heat cramps, but the patient IS dehydrated.Here, the patient has been unable to maintain body sodium and fluidrequirements, resulting in the symptoms of heat exhaustion. SYMPTOMS include: fatigue progressing to lightheadedness, nausea, vomiting, headache, rapid heartbeat while in a state of rest (100 beats per minute or more in the adult), and lowered blood pressure. Body temperature is normal, or only slightly elevated. Blood electrolyte abnormalities are commonly seen secondary to dehydration.

TREATMENT involves intravenous fluid administration under a physician's care. Seek treatment PROMPTLY.


This is the most serious heat illness and a true medical EMERGENCY. Heat stroke is often defined as a temperature of greater than 106 degrees Fahrenheit and the presence of a neurologic symptoms. People at risk are: the elderly, infants, athletes, construction workers, miners, new military recruits, persons
taking amphetamines, Mao inhibitors, phenothiazines, anticholinergics, or tricyclic antidepressants. Those with lack of sleep, exercise, or inadequate acclimatization to the environment are also at risk.
COMMON SYMPTOMS include: an ELEVATED temperature, LACK OF sweating, and often neurologic symptoms. Findings can be quite varied, including the occurrence of seizures, unresponsiveness, one-sided paralysis, or abnormal pupillary responses when light is shone into the eye(s). Early symptoms may include bizzare behavior, irritability, combativeness, or hallucinations. The patient may have fluid and body sodium depletion as seen in classic heat exhaustion. TREATMENT involves aggressive measures, applied quickly, to lower body temperature. Clothing should be removed on the scene, with cool water applied to the skin, followed by fanning. Ice packs to the groin and armpits are also useful. Intravenous fluid administration is often necessary to compensate for any associated fluid or electrolyte losses. These patients require IMMEDIATE emergency treatment.

Hope this article will provide you information about heat illness.

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