Hyperthermia (overheating or heat exhaustion) in cats and dogs
Hyperthermia is the term used to describe elevation in the core body temperature above the acceptable normal range. Where heat is produced or stored in the body at a greater rate than it is lost, hyperthermia ensues.
Because of their fur covering, dogs and cats are less efficient at being able to lose heat compared with humans. Animals rely on loss of heat by panting and external cooling; our domestic pets do not sweat and so do not have evaporative cooling. Heat stroke occurs when animals, more commonly dogs, are placed in a situation of low ventilation and high temperature or when they are exercised beyond their capacity to lose heat.
Hot cars and excessive exercise
Cars are a real problem in warm weather. Environmental temperatures of 24 degrees can exceed 48 degrees inside a locked car. So just 20 minutes at this temperature is enough to cause severe hyperthermia and death in a dog or cat. The problem is compounded more for the brachiocephalic breed – short muzzles or faces – as they are even less efficient at panting and ability to lose heat.
Exercise-induced hyperthermia can even occur in the absence of extreme heat or humidity. Exercise will cause a rise in core temperature due to sustained muscle activity. If the pet is not cooled and allowed time for its core body temperature to drop, it will suffer hyperthermia. Even sled dogs in heavy snow can suffer from hyperthermia if they are overworked in temperatures above zero degrees.
Each year our hospitals see dogs in a collapsed and hypothermic state that have been over-exercised in warm conditions. We also see dogs and cats in severe heat-stressed states where the owners have left them in a car for as little as 10 minutes while they 'duck inside' a shop or house or whatever.
We recommend that on even moderately warm days you only exercise your dog early in the morning and later in the evening. If your dog is heavily panting it is probably a sign that their core temperature is rising and that you should stop and let them rest. It is a good idea to carry a water spray bottle so you can wet your dog to cool them down. If you wet the face, under the arms and abdomen you will achieve the best result. Be aware of your individual pet’s tolerance for heat as this varies significantly between breed and individuals.
Signs of overheating – treat and bring the pet to our hospital
If your dog collapses or seems overheated, if possible wet its abdomen while getting it in the car. Ice packs can be applied around the neck and under the arm while you are on your way to our hosptial.
Once at the hospital we will continue cooling and provide oxygen and intravenous fluids. Cold water enemas may be required. Cooling needs to be controlled so as not to cause rebound hypothermia. Cooling too quickly can also shut down the peripheral skin vessels and actually inhibit the cooling process.
Hyperthermia can lead to a cascade of metabolic, cardiovascular and blood-clotting abnormalities. We will likely need to take blood samples and run tests, possibly over a prolonged recovery period. In uncomplicated hyperthermia the patient is usually discharged after 24 hours. Severe hyperthermia can require much longer in hospital depending on recovery and whether any organ damage has occurred.
Hyperthermia is usually preventable – with proper care on hot days, controlled exercise and never leaving pets unattended in a car. For more ways to safeguard your dog or cat during the warmer months, talk to our staff on your next visit to one of our Sydney Animal Hospitals.