Wilderness Medical Society snowmass 2005 Page 227
57
Chapter 13
HEAT-RELATED ILLNESSES
Recommendations are considered Category 1B by the WMS Panel of Expert Reviewers.
I. GENERAL INFORMATION
Heat-related illnesses comprise several conditions caused by exposure to hot
environments, or intense exercise in moderate environments, that range from mild
discomfort to life-threatening illness. Hyperthermia occurs when heat stress on the body,
from internal metabolic heat production and external sources, overcomes the heat
dissipating capability of the body. Extreme or untreated hyperthermia can rapidly become
life threatening.
Heat illnesses are preventable. Prevention includes:
1) Acclimatization, the process by which the body adapts to heat exposure, is induced by
a minimum of 60 to 90 minutes of exercise in the heat each day for one to two weeks.
Initial adaptation occurs within a few days. The most significant change is an increase in
sweat volume initiated at a lower skin temperature. This increases evaporative cooling
and results in a lower heart rate and core temperature for a given amount of work in the
heat.
2) Hydration with adequate fluid quantities. An acclimatized person can lose one L/h or
greater of sweat during exercise. Relieving thirst alone risks not maintaining full
hydration. Start each work period by drinking 500ml of water. At least 300-500 mls per
hour is then likely to be required, and requirements may be higher with extreme exertion
or sweat loss. (see Oral Fluid and Electrolyte Replacement) In extreme conditions, sweat
loss may exceed gastric emptying and intravenous fluids may be required.
3) Dress appropriately in light-colored, loose-fitting clothing, allowing maximum
evaporative heat loss.
4) Frequent rest, especially before full acclimatization, preferably in shade during the
hottest part of the day.
5) Maximize evaporative cooling by dipping clothing periodically in water, if possible.
6) Physical fitness improves the rate and quality of acclimatization, but does not provide
heat adaptation by itself. The insulation of excess body fat reduces heat loss.
II. GUIDELINES FOR ASSESSMENT AND TREATMENT
A. Heat cramps are muscle spasms that may be severe, usually in large, heavily exercised
muscle groups like legs and abdomen. They are probably caused by a combination of
electrolyte depletion, hyperventilation with respiratory alkalosis, and plasma volume
depletion. Rest the patient and give oral or intravenous fluids that contain sodium. Cold
oral fluids are absorbed more quickly than warm ones. Gentle stretching of the cramped
muscles is usually beneficial. After recovery, the activity may be resumed, but if the
cramps return, a 24-hour rest is recommended.
B. Heat syncope is seen immediately after periods of strenuous work in hot
environments. Patients regain consciousness quickly. Treat with recumbent rest in a
