Heatstroke and Animals: 

Why You Shouldn’t Leave Your Dog in a Parked Car

By Nancy Otten, Animal Health Technologist

What happens to dogs when we leave them in parked cars?

We all know that it’s dangerous to leave your dog alone in a parked car for any period of time, especially in the summer.  Even on days when it’s just mildly warm or even cool, temperatures can rise to dangerous levels within 10 minutes.  The dog’s body will try to compensate for the sudden rise in temperature.  When the dog’s body temperature becomes too high, thermo receptors send signals to the thermoregulatory centre (the hypothalamus.)  The hypothalamus sends signals to the blood vessels in the skin and to the respiratory centre in order to start the compensation processes.  The blood vessels in the skin will dilate (increase in diameter) and the heart rate will increase in order to increase the amount of blood going to the skin.  By doing this, the body is able to send more blood to the surface of the skin to be cooled by the ambient air.  Unfortunately, in parked cars, the hot ambient air is what is causing the problem so this compensation mechanism is ineffective.  The hypothalamus also sends signals to the respiratory centre to start the process of panting.  Panting uses the principle of evaporation to cool the body.  When a dog pants, his breathing becomes very rapid and shallow in order to increase the airflow into his respiratory tract without increasing oxygen intake or carbon dioxide loss.  By doing this, he uses the evaporation of the fluid in his mouth and lungs to increase heat loss.

What happens when it gets so hot that the dog can’t compensate anymore?           

When the dog can’t compensate anymore, he begins to suffer from heatstroke.  In the early stages he’ll be panting, the mucous membranes (e.g. gums) will be bright red and his heart rate will be high.  Eventually this extreme dilation of the surface blood vessels takes its toll by lowering the blood pressure to a point where the vital organs aren’t getting enough oxygen.  This lack of oxygen causes cell death.  The body then has to compensate for that by going into shock.  The surface blood vessels are constricted in order to increase blood pressure and the flow of blood to the organs.  At this stage of heatstroke, the mucous membranes would be gray and the pulse would be weak.  Insufficient oxygen levels aren’t the only thing that causes damage to cells.  The heat itself causes injury.  When the animal goes into shock and the blood is shunted to the vital organs, this hot blood literally cooks the organs.  The blood cells themselves become cooked so that they can’t carry out their normal functions.  The digestive tract can become ulcerated causing vomiting and diarrhea.  Damage to the central nervous system can cause a coma.  Your dog’s liver and kidneys can fail.  All organs and tissues can be affected and can suffer irreparable damage.            

What happens if we screw up and we leave our dog in the car?  What can we do to save him?

Heatstroke should be considered an extreme medical emergency.  The key to initial treatment is to lower the core body temperature.  It is important to get the dog out of the car as soon as possible and into a shady area.  Don’t pour cold water over the dog or throw him into the lake.  All you will accomplish is to constrict those surface blood vessels and to send all of that hot blood to the vital organs.  You need to bring the dog’s temperature down slowly and make your way to a veterinarian as soon as you can.  You can wash the body down with warm to room temperature water to facilitate evaporative cooling.  Fanning the dog will help this process.  If large quantities of warm water aren’t available, compresses of cool water can be placed in the dog’s armpits to cool the blood flowing through the large blood vessels found there. Massage the body to promote peripheral blood flow and the dilation of these surface blood vessels.  If the animal is still conscious and responsive, offer him water because all of the compensatory panting will have dehydrated him.  If the animal begins to shiver, stop all cooling methods immediately.  Shivering will produce more heat.  It is important that the dog’s body temperature be monitored closely.  His thermoregulatory system may have been damaged by the heat so he may not be able to maintain his body temperature at the appropriate level once it is achieved.  The last thing he’ll need is to suffer from hypothermia (low body temperature.)  Once at the veterinary clinic, the vet may decide that your dog has suffered severe dehydration and needs IV (intravenous) fluids.  In addition to the use of water and fanning, he may also try to lower your dog’s temperature by chilled IV fluids or a cold water enema.  A thorough exam will be done to look for signs of organ and tissue damage.  Blood tests may be needed to help determine this.  Sometimes it takes a while to discover what damage has been done so the dog will need to be monitored closely for several days.