Hypothermia and Frostbite
January, 1997
Although cold weather is little more than a nuisance to us, it
can be a cause of serious injury or death to our dog if prolonged
exposure is not prevented. This is especially true if the dog is
very young, old, sick or has not been properly acclimated to cold
temperatures. Hypothermia results when the core body temperature
falls well below normal. Rectal temperatures in normal dogs range
from 101.5 - 102.5 degrees Fahrenheit. Low temperatures interfere
with many enzyme systems and metabolic activities, so hypothermia
affects virtually all organ systems in the body.
The body thermostat is located in a portion of the brain called
the hypothalamus. It is responsible for maintaining a balance
between heat production and heat loss. The major source of heat
production in the body arises from muscle activity, with food
digestion and metabolism as secondary sources. Heat is lost to
any environment which the ambient temperature is below the body’s
temperature. Some natural responses in a cold environment that
help prevent hypothermia include shivering (to increase muscle
activity and, therefore, heat production) and shifting of blood
from extremities to more essential organs. This alteration in
blood flow, along with decreased enzyme systems, accounts for
most of the organ dysfunction seen with hypothermia.
The initial response of the heart to mild hypothermia is an
increase in heart rate and blood pressure, but with increased
time or severity of hypothermia, heart rate and blood pressure
decline. More severe hypothermia causes cardiac arrhythmias and
other EKG abnormalities or cardiac arrest. Similarly, respiratory
changes seen with mild hypothermia include an increased
respiratory rate, but eventually there is a respiratory
depression. Poor clearance of the airways makes a dog susceptible
to pneumonia. Initial neurological signs include intense
shivering, then lethargy and suppressed reflexes which can
progress to incoordination, paralysis, unconsciousness and
collapse. Hypothermia also affects the coagulation ability of the
blood and causes other changes that show up on routine blood
tests and urinalysis.
Treatment is accomplished by rapid warming of the body. For mild
cases, this can be done by external means such as hot water
bottles, heating pads or immersion in warm water. More severe
cases may require internal warming using pre-warmed fluids given
intravenously, by dialysis, or as an enema. Veterinarians may
make use of corticosteroids. It is also important to monitor the
dog for heart arrhythmias, pneumonia or frostbite.
Frostbite occurs when a single body part is damaged from
prolonged exposure to cold air or contact with cold metal. Lower
temperatures require shorter times to cause severe damage.
Frostbite usually affects extremities, due to their more limited
blood supply and the fact that the hair cover may be sparse. The
most commonly affected areas are the toes, the tail, the scrotum
and ear tips. A hound dog’s flapping ears are usually not as
susceptible as those of an erect-eared dog.
Frostbitten tissues are usually pale, cold and lack sensation.
Eventually, there may be redness, swelling and pain. During the
first three days of healing, it is probably impossible to tell
which affected tissue will die and which will heal. Any tissue
that does not start to improve three to four days after rewarming
should be amputated, as it will likely undergo dry gangrene, or
mummification. Mummified tissue is permanently dried out and hard
to the touch. Any tissue that has survived frostbite will likely
be more susceptible to future damage from the cold.
As with most diseases, prevention of hypothermia and frostbite is
more useful than treatment. A healthy adult dog can become
acclimated to cold weather so that it may withstand below-zero
outdoor temperatures, if kept in a well insulated house. Hunting
in the cold for hours is safe if the dog has adapted to it over
time, especially if he keeps moving and is not allowed to rest on
the frozen ground for an extended period of time. Using common
sense as your guide, severe injury to your dog from exposure to
the cold can be prevented.