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Chapter 11
HYPOTHERMIA
Recommendations are considered Category 1B, except were indicated 1A, by the WMS
Panel of Expert Reviewers.
I. GENERAL INFORMATION
Hypothermia occurs when the body's ability to generate and conserve heat is overcome
by heat loss. Acute hypothermia presents with a sudden drop in body core temperature
within a few hours. This is usually caused by immersion in cold water or a sudden drop in
ambient temperature combined with wind and precipitation. Chronic hypothermia is the
result of a gradual drop in body core temperature over several hours. Most chronic
hypothermia deaths occur when the ambient temperature ranges from 30 to 50
o
F (-1 to
10
o
C). Hypothermia is almost always preventable by minimizing heat loss via
conduction, convection, radiation, and evaporation. Prevention includes 1) proper choice
and use of clothing and shelter, 2) avoidance of overexertion, 3) staying dry (a
combination of proper clothing and avoidance of overexertion), 4) staying well-hydrated
and 5) maintenance of adequate nutrition.
A. Mild Hypothermia: Hypothermia is considered mild if the core temperature is below
95
o
F (35
o
C) and above 90°F (32
o
C). In this temperature range, the thermoregulatory
defense mechanisms, such as shivering, are generally unimpaired and operating
maximally. Mild hypothermia often first manifests itself as loss of judgment and fine
motor coordination. Shivering is often suppressed by physical activity, but by the time
core temperature reaches 95
o
F (35
o
C), most patients are shivering vigorously.
Uncontrollable shivering will be seen during further cooling to 90°F (32°C), except in
some chronic exposure situations (>6-8 hours) where exhaustion and shivering fatigue
may occur. Slurred speech, a stumbling gait and the development of ataxia are highly
suggestive of hypothermia in a cold-exposed patient. It is important to note that most
patients with mild hypothermia are fully able to rewarm themselves through shivering
heat production, although they require protection from further heat loss in order to do so.
The exception will be an exhausted patient who is unable to shiver.
B. Moderate-to-Severe Hypothermia: Hypothermia is considered moderate at core
temperatures below 90°F (32°C) and above 82°F (28°C), and severe at core temperatures
below 82°F (28°C).
Since taking core temperature measurements may not be possible or appropriate in the
field, diagnosis can be based on observations and functional characteristics.
As core temperature decreases within the moderate range, thermoregulatory
shivering is progressively inhibited until it stops and the patient loses the ability to
rewarm (usually at a core temperature of about 86°F (30°C). The patient may have a
profoundly altered mental status, loss of coordination, lassitude and an apathetic attitude.
Finally, consciousness will be lost.
