Encyclopedia of Health and Medicine

Heat and Cold Injuries
Heat and cold injuries most often occur in
response to environmental exposure to extremes
in temperature. Environmental temperatures that
are above or below the body’s normal temperature
require the body to implement actions to
compensate. When the external temperature is
higher than body temperature, these actions
include peripheral vasodilation (BLOOD vessels in
the extremities relax to increase the flow of
blood), which moves greater quantities of blood
closer to the body’s surface where the temperature
is somewhat cooler, and sweating, which
cools the SKIN through evaporation.
When the external temperature is lower than
body temperature, the body’s compensatory
mechanisms include peripheral vasoconstriction
(blood vessels in the extremities narrow to
decrease the flow of blood), which pulls more
blood within the body core where temperature is
somewhat warmer, and shivering, which
increases energy output that in turn raises body
temperature. When either set of mechanisms fails
to achieve an acceptable body temperature, body
chemistry and METABOLISM begin to change, altering
vital body activities such as neurologic (BRAIN),
cardiovascular (HEART rhythm and BLOOD PRES-
SURE), and renal (kidney) functions.
A person’s body size and composition and
activity level also influence the rate at which the
body retains or loses heat. A person who has fairly
high body fat loses body heat more slowly; he or
she may have better tolerance for exposure to
cold and less tolerance for exposure to heat. For a
person who has low body fat, the reverse is the
case: He or she often has better tolerance for
exposure to heat and less for exposure to cold.
Moisture further influences the extent to
which such exposure is tolerable or becomes a
health concern. In cold water or when wearing
374
wet clothing a person loses body heat at a rate up
to 20 times that which occurs in cold air. Wind
also influences the effects of cold; a calculation
called the wind-chill factor represents the effect.
Moisture similarly affects the consequences of
heat. High humidity in combination with high
temperature intensifies the risk for heat injury; a
calculation called the heat index represents the
effect. HEAT EXHAUSTION and HEAT STROKE, the two
types of heat-related injuries, most often occur in
people who are engaged in intense physical activity
in circumstances of combined high temperature
and high humidity. DEHYDRATION can occur
rapidly with heat injuries, further complicating
health concerns.
Untreated, progressive heat or cold injury has
high risk for permanent tissue and organ damage
or death.
dehydration Insufficient water intake or excessive
water loss resulting in electrolyte imbalance
within the body. Though there are numerous possible
causes for dehydration, the most common
first aid scenario for dehydration occurs with athletic
activities, sporting events, intense physical
labor (especially in hot conditions), and extremely
hot weather.
Early symptoms of dehydration include thirst,
light-headedness, and dry SKIN. Drinking cool
water, to 6 ounces every 15 minutes, is often adequate
treatment for mild dehydration. Symptoms
of moderate dehydration may include mild MUSCLE
cramps, mental confusion, and disorientation.
Though drinking water may improve moderate
dehydration as a first aid response, intravenous
fluids are often necessary to restore electrolyte
balance. Severe dehydration may result in loss of
CONSCIOUSNESS, rapid or irregular HEART RATE
(tachycardia or ARRHYTHMIA), rapid BREATHING,