Winter is rapidly approaching – at least here in North America. With the advent of this season comes bone-chilling temperatures in many regions. Dogs and cats – just like humans – are at risk for developing subnormal body temperatures, a condition known as hypothermia. This week I’ve dedicated some blog space to spreading the word about this adverse condition to raise awareness. Happy ready!

Hypothermia – What is it?

Hypothermia is a state of lower-than-normal body temperature. The normal body temperature for dogs and cats ranges from 100.5°F to 102.5°F. Hypothermia is classified as primary or secondary:

• Primary – this form is due to environmental exposure despite normal heat production by the body
• Secondary – this form is due to alterations in heat production because of illness, injury, or drugs.

Hypothermia – Why does it happen?

The body can lose heat through four basic mechanisms. Convection transfers heat from the body surface to air or water moving past the animal. Conduction transfers heat from the body surface to colder objects in contact with the skin. Radiation is the exchange of heat between the body and objects in the environment that are not in contact with the skin, independent of the temperature of the surrounding air. Evaporation occurs when moisture in contact with skin or the respiratory tract dissipates into the air

One of the most common contributors to hypothermia in veterinary medicine is placing pets under anesthesia to perform surgery and/or diagnostic tests. Patients breathe cold, dry air delivered directly to the lungs. Routine aseptic preparation of surgical sites promotes evaporative heat loss. Cold table surfaces and open body cavities exacerbate heat loss through conduction and radiation, respectively. Anesthetic agents contribute to hypothermia by:

• Negatively affecting the temperature control center in the brain
• Causing peripheral blood vessels to dilate
• Reducing a patient’s metabolic rate

Veterinarians strive to minimize the duration of anesthetic and surgical procedures to help reduce the incidence of secondary hypothermia.

Hypothermia – Why is it potentially harmful?

There are many potential complications associated with primary and secondary hypothermia, including:

• Cardiovascular – the heart rate slows down, electrical activity in the heart is altered, and the tone of blood vessels is dramatically reduced.
• Lungs – the breathing rate slows down, breaths are shallow, and oxygenation and ventilation are compromised.
• Organ function – blood glucose drops; the clotting system is compromised, and the kidneys may fail.
• Nervous system: patients are often depressed and can slip into comas
• Immune system – the immune system is impaired and can’t fight infection as effectively; wounds don’t heal properly.
• Skin – dogs and cats can develop “frost bite” just like people exposed to extremely cold temperature. The paws and the ears are most commonly affected.

Hypothermia – How is it treated?

The best treatment for hypothermia is preventing it from occurring in the first place. Alas, that is often much easier said than done. Thus, therapeutic efforts are aimed at rewarming patients and reducing additional heat loss. Veterinarians rewarm hypothermic animals via several different methods, including:

• Passive surface strategies (e.g., room temperature blankets)
• Active surface strategies (e.g., heated blankets, circulating heated water beds)
• Active core strategies (e.g., administering warmed intravenous fluids)

A dog receiving active surface rewarming via a forced air warming blanket. Photo courtesy of Advanced Anesthesia Specialists.

Hypothermic patients should not be submerged in warm water, as doing so can trigger life-threatening blood pressure changes and abnormal heart rhythms. Veterinary medical teams will closely monitor many parameters in hypothermic patients, including electrolytes (e.g.: sodium, potassium), heart rhythm, blood pressure, and blood oxygenation. Once hypothermia has been corrected, the various abnormalities often normalize quickly,

The take-away message about hypothermia in dogs and cats…

When body temperature drops due to environmental exposure, surgery, or illness, the body faces many unique challenges. Without prompt correction of hypothermia, patients will develop potentially life-threatening complications. While aggressive and early treatment typically results in a positive outcome, prevention of hypothermia is the preferred intervention.

To find a board-certified veterinary emergency and critical care specialist, please visit the American College of Veterinary Emergency and Critical Care.

Wishing you wet-nosed kisses,

CriticalCareDVM