Heat Stroke, Hyperthermia

Hot vehicles fit for neither man nor beast in summer

Barry Burtis, Pet Tales

There are some pet health warnings that just need to be repeated and repeated.

Most people are aware of the danger associated with leaving a pet in a car without adequate ventilation. Nevertheless, every year pets die or suffer serious injury because owners forget the danger heat stroke or hyperthermia can pose to animals.

Let's review the basics of the problem.

Hyperthermia is an elevation of the core body temperature. It is generally accepted that body temperatures above 39 C (103 F) are abnormal. A dangerously high temperature can result from things happening inside a pet's own body, such as a fever, muscle fasciculations or a seizure. It can also happen as a result of excessive external heat, as happens in heat stroke.

It is also important to remember there are other causes of heat stroke besides being left in a car in the heat of summer. Dogs are more susceptible to the problem than other animals. This is partly due to their inability to dissipate body heat very effectively because dogs can only perspire from their nostrils and foot pads -- very small areas compared to their overall body surfaces.

Very young animals and geriatric animals, especially those with pre-existing disease, are at higher risk to suffer heat stroke.

It can happen in any breed, but there are certain breed and genetic factors that predispose some animals to the problem. Brachycephalic breeds, those dogs with short noses, flat faces and prominent eyes, like pugs, Pekingese, boxers and bulldogs, are at greater risk to have problems. Obese or overweight animals, dark-coloured and long-haired dogs also have heightened susceptibility.


In our geographical area, it is more likely to be a health concern in the early summer when pets have not yet had an opportunity to acclimatize to changing air temperatures and people may have forgotten how quickly temperatures can change inside a car or with exercise.

Remember that point about exercise. Exercise is good and jogging with your dog or having a good workout at the beach with your favourite canine is fun, but don't overdo it when the hot days arrive. Dogs, in their exuberance over play and activity, will likely forget they are heating up and need to slow down a bit. It's another time when it's up to the owner to recognize what's best for their dog.

Cats and dogs, unable to evaporate water by sweating and thereby lower their body temperature, instead pant. It is just another way of evaporating moisture and act as a cooling force.

Any pet that is being affected by hyperthermia will likely first begin to pant. An observant pet owner should recognize panting as a warning signal that may indicate their pet needs to turn whatever they are doing down a notch.

Excessive panting may mean that a more serious stage of heat stroke has developed. As the condition continues, the pet may collapse and be unable to rise. Vomiting and/or diarrhea will often occur as the problem worsens. If an animal is found with these signs in a place where it is extremely warm such as a car, a clothes dryer, an attic or other poorly-ventilated room, it should be even more obvious what is causing the problem.

In an animal that becomes hyperthermic, a very complex and destructive sequence of events is triggered. With hyperthermia, body temperatures of 41 C (106 F) often develop. The critical temperature that leads to multiple organ dysfunction is 42.7 C (109 F).


Inflammatory processes are activated and cytokines are produced. Body tissues that line various body organs, including heart and blood vessels, may be damaged as the core body temperature is elevated. These changes can in turn lead to failure of the blood circulatory system.

Cerebral edema may result from damage that occurs to the process regulating transfer of materials between the brain and circulating blood. Unless these changes can be stopped and reversed, death may occur.

Early recognition of the problem is the key to successful treatment of heat stroke.

Immediate correction of the hyperthermia is critically important. If an animal is found in such a condition, there should be some external cooling techniques begun even before transporting to a veterinary facility, if that is possible. The animal should be sprayed with water or immersed in water. Cooling with fans could be started.

It is best not to use ice to cool the affected pet, as this may cause superficial blood vessels to constrict and impede heat dissipation. A shivering response is also undesirable, as that process generates heat.

In an animal hospital, further life saving measures can be instituted. Continuous body temperature monitoring is important in determining appropriate therapy.

Intravenous fluid therapy, oxygen supplementation and measures to support breathing are usually the most important components in treatment procedures. A pet that successfully recovers may have sustained damage to the thermoregulatory centre in the brain. This means they will be more susceptible to heat stroke episodes in the future.

Enjoy all the activities and events of the summer season with your pet, but use good pet care rules and keep it cool when you do.