Summary
Hypothermia is a lowering of the body's temperature.
At a rectal temperature of less than 28°C (82°F), the ability to regain normal temperature
is lost, but the animal will continue to survive if external heat is applied and the
temperature returns to normal. It is important to observe and measure the vital signs:
pulse, breathing, mental status and rectal temperature. To know the severity of
hypothermia is valuable to decide the re-warming technique to be used for treatment. On
the basis of body temperature, hypothermia can be classified as Mild (86-89° F or 30-32°
C), Moderate (71-77°F or 22-25°C) and Severe (32-46.5°F or 0-8°C). There are three
rewarming techniques (Passive external, Active external, and Active internal) which should
be used according to severity of hypothermia.
Due to limited literature in veterinary science, the
authors have obtained relevant information from the medical field on human hypothermia.
The information presented in this article has been obtained from various sources (see
references). In our views, this information is likely to be a valuable in treating
hypothermic animals, however, we advise practitioners to use this knowledge along with
their experience in dealing with hypothermic patients.
Hypothermia is a lowering of the body's temperature.
When the skin or blood is cooled enough to lower the body temperature in non-hibernating
animals, the metabolic and physiological processes slow down. In the hypothermic state,
the oxygen need of cells, particularly neurons is greatly reduced, and the circulation can
be stopped for relatively long periods. At a rectal temperature of less than 28°C (82°F),
the ability to regain normal temperature is lost, but animal will continue to survive if
external heat is applied and the temperature returns to normal. Hypothermia is a condition
of general body cooling in contrast to frostbite, which is localized.
A fall in body temperature can be due to accidental
exposure to external cold, effect of drugs, or failure of internal temperature regulating
mechanisms.
The simplest way to determine whether the patient is
hypothermic or not, is to assess body temperature by placing a bare hand against the skin
(preferably in axilla or groin region) of the patient. If the skin feels warm, hypothermia
is unlikely. Patients with cold skin should have rectal temperatures taken with a low
reading thermometer.
What to expect in a hypothermic animal?
As the body core temperature drops, more body
systems suffer from the effects of cold. The signs and symptoms can assess the presence
and severity of hypothermia. In the cold patient, a rectal temperature is one of the most
important signs and is useful for assessing and treating hypothermia, however there is a
tremendous variability in physiological responses at specific temperatures among
individuals and species.
Once it is established that an animal is hypothermic
it is important to observe and measure the following most important signs: pulse (slow to
none); breathing (slow to none); mental status (responsive to unconsciousness); cold skin;
low rectal temperature.
Severally hypothermic animals may have other
problems, which are not easily detected. e.g. change in blood chemistry; irregular heart
beat; dehydration; difference in temperature between deep body tissues and superficial
body tissues.
Classification on the basis of severity
On the basis of body temperature, hypothermia can be
classified as Mild (86-89°F or 30-32°C), Moderate (71-77°F or 22-25°C) and Severe
(32-46.5°F or 0-8°C).
Management of a hypothermic animal
The primary goals in the treatment and handling of a
hypothermic animal are: keep the animal alive by warming, avoid any further exposure to
cold, and then transport the animal to a site of complete veterinary care.
In order to treat the hypothermic animal
appropriately, one should first know that the animal is in fact hypothermic. If so, then
the severity of hypothermia e.g. mild, moderate or severe. Once this is determined, one
has to decide the re-warming technique to be used for treatment.
Examination of hypothermic animal
To examine a hypothermic animal, one should proceed
as follows:
1. Attention to
ABCD: A. Airway; B. Breathing; C.
Circulation; D.
Degrees. One should make sure that the animal has an open airway, is
breathing, and has a heart beat and assess rectal temperature.
2. Brief history (e.g. duration of exposure,
regarding circumstances in
which animal found etc.).
3. Brief physical examination including a) feel of
body temperature. b)
level of consciousness and neurological examination. c) cardio-pulmonary
examination. d) associated trauma e) weight of animal. Depending upon
the availability of staff and equipment, chest x-ray, urinalysis,
complete blood work, and arterial blood gases are also recommended.
If there is a high probability that the animal is
severely hypothermic, breathing and heart rate may be slow, shallow and very hard to
detect, therefore, take a full minute or more to measure these vital signs.
Hypothermic patients with any measurable pulse or
respiration obviously do not require Cardio - pulmonary Resuscitation (CPR). However, if
both pulse/heart beat and respiration are absent then commence CPR.
Evaluate the animal's level of consciousness, size
of pupil, ability to respond if conscious and ability to walk. When any of these
characteristics are abnormal, suspect severe hypothermia and treat accordingly. While
treating the hypothermic animal, also check the animal for other possible injuries. The
best chances of recovery are as a result of early diagnosis and treatment.
In accidental hypothermia, the animal should be
brought into a heated environment and allowed to warm slowly to its normal temperature.
Rewarming and maintenance of normal body temperature can be accomplished externally or
internally (see Rewarming techniques). Neonates not only require rewarming but careful
attention to nutrition
should also be given.
Mild hypothermia: Prevent further heat loss,
insulate from the ground, protect from the wind, cover the head and neck, and move the
animal to a warm environment. Rewarming through the application of insulated heat packs to
high heat loss areas such as head, neck, between legs, side of chest wall to prevent heat
loss. Consider warm showers and warm bath, if the patient is alert (see passive external
and active external rewarming techniques)
Moderate hypothermia: Keep the patient warm e.g.
warm bottles, blankets, immerse patient in tub of warm water. Continue rewarming efforts
until animal's core temperature is restored to normal (see active external rewarming
methods).
Severe hypothermia: Animal in severe hypothermic
state, can erroneously thought to be dead as no pulse, no heart rate, and no respiration
is apparent. It is wise to follow the same criteria as in human medicine which suggests
" the hypothermic patient is not dead until the patient is warm and dead."
Animals with severe hypothermia should be treated by
putting heat directly into the core areas (see active rewarming methods). If the heart
beat and respiration is not detectable after checking for up to 1 minute then commence
CPR: Mouth to mouth or mouth to mask breathing during CPR is best because this provides
warm, humidified air or oxygen. One can also use an apparatus to ventilate the animal with
100% heated, humidified air or oxygen. Reassess the animal's physical status periodically
while performing CPR. CPR is less likely to have a significant effect on the survival of a
hypothermic animal, if
a) The animal has been under the water for more
than 1 hour.
b) The animal with a core temperature below 60 F
(15.5 C).
c) The animal is frozen e.g. ice formation in the
airway.
d) The animal's chest wall is so stiff that
compression is impossible
Treatment that stimulates peripheral circulation
(i.e. wrapping in a blanket, massaging extremities etc.) must be avoided in cases of
severe hypothermia. These activities will likely increase flow of cold blood from the
periphery (muscle pumping) which can cause after drop, increasing the depth of hypothermia
in critical core tissues, especially the heart. Stimulating the peripheral circulation
also reduces the blood volume in the body core, causing rewarming shock, which increases
the workload on the heart. The blood returning from the periphery can also include
metabolic waste products that can cause a fatal heart arrhythmia.
Rewarming techniques
There are three classes of rewarming techniques:
1. Passive external: The animal's own metabolic
processes continue to
produce heat spontaneously so no external heat is required. Shivering
is an example of thermogenesis. This is simplest and slowest rewarming
method but is sufficient for mild hypothermic patients.
2. Active external: This system includes warm
water baths, hot water
bottles, blankets, heating pads, radiant heaters. This method of
rewarming is safe only for mild hypothermia because externally applied
heat stimulates peripheral circulation.
3. Active internal: These rewarming methods are
usually more complex and
need to be carried out by professionals (Veterinarians/Animal health
technicians). These include inhalation rewarming (ventilation of
patient with heated, humidified air or oxygen), circulation of heated
fluids (40.5-43.5°C) in body cavities (gastric, thoracic and
peritoneal lavage), and heated intra venous solutions preferably
dextrose as this provides energy to meet increased metabolic demands
(contribute little heat due to vasoconstriction in cold extremities).
Inhalation rewarming is the only method, which can be used by a layman
and does not require much training (mouth to mouth breathing).
Inhalation of warm-saturated air delivers heat directly to the lungs and
heart. The brain is also warmed from this blood flow and from
conductive heat flow from the respiratory and nasal cavities. This
method also assists in re-hydration as an added benefit.
Precautions while treating hypothermic
animals
1. Be cautious about assuming that animal can not
be resuscitated. As
in resuscitation, a positive attitude is important. The hypothermic
animal may appear to be beyond help because of, skin and membrane
colors, pupil dilatation and depressed vital signs.
2. Avoid direct application of hot objects or
excessive pressure (e.g.
uninsulated hot water bottles, tourniquets etc.). Ensure that items such
as oxygen and fluids coming into contact with the animal are warmed.
3. Do not put severely hypothermic animal in a
shower or bath.
4. Drug treatments are not useful in treating
severe hypothermic animals
since the cold heart will not respond as expected. If administered,
drugs will not be metabolized normally by the liver and kidneys; instead
these will accumulate in the body and become active as it warms.
5. Do not use Lactated Ringers because the
hypothermic liver may not be
able to metabolize the lactate normally.
6. Do not administer cold fluids.
Information Sources:
The Merck Veterinary Manual: A handbook of
Diagnosis, Therapy, and
Disease Prevention and Control for the veterinarian. Edited by Clarence
M. Fraser. Published by Merck & Co., Inc. Rahway, N.J., U.S.A.
Saunders Manual of Small Animal Practice Edited by
Stephen J. Birchard
and Robert G. Sherding. Published by W.B. Saunders Company (1994).
Dhupa Nishi (1995). Hypothermia in Dogs and Cats.
Compendium. CE
Series: Emergency Medicine/Critical Care. Vol. 17. 61-68.
Alaskan Protocol: State of Alaska Cold injuries and
Cold water near
drowning Guidelines (Rev. 01/96).
http://hypothermia.org/protocol.htm
Hypothermia Prevention, Recognition and Treatment.
Journal of the
American medical Association. Vol. 268. (16), 1992.
http://hypothermia.org/jama.htm
Hypothermia 1: Hypothermia rescue response.
Published by Robert Douwens
(Internet) with permission from author CDR. DR A.M Steinman, USPHS.U.S.
Coast Guard On Scene Magazine.
http://hypothermia.org/hypothermia1.htm
Hypothermia 2: Survey on Inhalation rewarming.
Published by Robert Douwens.
http://hypothermia.org/hypothermia2.htm
Hypothermia 3: Rescue.
Published by Robert Douwens.
http://hypothermia.org/hypothermia3.htm
Hypothermia information. Michael R.
Schmehl..
http://cac.psu.edu/~jxm181/scouts/winter/hypothrm.html
Hypothermia -The Silent killer. Gary R,
EMT-D.
http://cac.psu.edu/~jxm181/scouts/winter/hypsikil.html
Physical symptoms of Hypothermia. Smokey S.
http://cac.psu.edu/~jxm181/scouts/winter/physmhyp.html
RES-Q-AIR