Heat stroke is a condition arising from extremely high body temperature (rectal temperature of 105 to 110 degrees F), which leads to nervous system abnormalities such as lethargy, weakness, collapse, or coma. Abnormally high body temperature develops after increased muscular activity with impaired ability to give off heat due to high heat and humidity or respiratory obstruction. Allowing a dog to remain in a car with closed windows on a hot summer day is probably the most common cause of heat stroke.

Normal dogs dissipate heat from their skin. In addition, panting allows evaporation of water from the respiratory tract and is an effective method of heat dissipation. When these mechanisms are overwhelmed, hyperthermia and heat stroke usually develop. At temperatures greater than 109 F, failure of vital organs, and consequently death, can occur.

Heat-related illnesses, including heat stroke, heat exhaustion, and heat cramps can occur after exposure to extremely high environmental temperatures. These illnesses occur in all mammals and can be prevented by taking proper precautions.

Animals at greatest risk for heat-related illness include:

• Puppies up to 6 months of age
• Overweight dogs
• Dogs that are overexerted during exercise
• Dogs that are ill or receiving certain medications
• Dogs with short, wide heads like pugs, English bulldogs and Boston terriers
• Dogs with airway obstructive diseases
• Dogs with pre-existing fever
• Dogs that are dehydrated
• Dogs with heart disease
• Dogs with poor circulation due to cardiovascular or other underlying disease
• Older pets

What to watch for:

• Noisy breathing that may indicate upper airway obstruction
• Excessive panting
• Bright red mucous membranes (gums, conjunctiva of the eyes)
• Weakness
• Collapse
• Coma

Diagnostic tests are needed to diagnose heat stroke and assess the extent of vital organ dysfunction, including:

• A complete medical history and thorough physical examination, including rectal temperature.
• A complete blood count (CBC) to assess the severity of dehydration and cardiovascular stress.
• Coagulation tests to determine if there is a failure in blood clotting that is often a complication of heat stroke.
• Blood tests to check blood glucose concentration, assess the extent of damage to vital organs, such as muscles, kidneys and liver to evaluate the electrolyte and acid base status.

The treatment of heat stroke depends upon the severity of the illness. Animals with temperatures less than 105 F may only require rest, fresh water, and careful observation. Temperatures of 105 to 107 should be hospitalized on intravenous fluids. Temperatures over 107 must be treated more aggressively and cooling can be promoted externally by immersion in cool water or internally by administering a cool water enema. Additional treatments may be needed if secondary complications arise such as: liver failure, kidney failure, muscle breakdown, low blood pressure, low blood sugar, convulsions, and secondary infections.

Heat stroke is a life-threatening emergency, but there are several things you can do to prevent heat related problems for your dog. Monitor outdoor temperatures and minimize your dog’s activity on hot, humid days. NEVER leave your dog in a car, even with the windows partially rolled down, for any reason at any time.Leaving dogs in a car during warm weather is the most common cause of heat stroke. Provide your dog with plenty of fresh water and plenty of shade.