Heat Stroke

The following article was written by Rachel Peeples.

The dog regulates its body temperature differently than humans do.  The most striking difference is that they do not have an entire body for sweat to evaporate off of to cool them and, thus, have to rely on panting as the primary means of cooling their bodies.  Anything that prevents the ability to pant effectively will prevent the animal from adequately cooling itself.  Such things include laryngeal paralysis (common in older Labradors), brachycephalic head conformation (Bulldog, Boxer, Pug, Pekinese, etc), a mass compressing the trachea (windpipe), and tracheal collapse (common in small breed dogs).  In addition to panting, dogs get rid of heat from the skin not so much via sweat evaporation but from a process called convection (heat dissipates from an area of high heat to an area of low heat) in which heat leaves the skin into the air. Therefore, conditions that reduce the ability of the heart to adequately send blood to vessels in the skin and thereby allow heat from the blood to go into the air across the skin will also hinder a dog's ability to properly cool itself and maintain the proper body temperature.  Such conditions include heart disease, obesity, and dehydration.

Anytime that a dog is unable to cool itself enough to prevent its temperature from increasing out of normal limits it is at risk for heatstroke.  Dogs with the aforementioned conditions can experience this just with normal everyday activity when it is warm to hot.  These dogs should be kept cool and quiet when the weather is hot.   Normal dogs (i.e. those without these predisposing factors) are able to adapt to a much greater extent.  But sometimes we humans put them into positions where they are simply unable to keep themselves cooled off even with everything functioning maximally.   Such a situation we create by leaving a dog in a car with the windows up on a sunny, warm to hot day where car temperatures rise to 140 degrees or more.  Other situations include the outside dog without adequate shade and / or water, extreme exercise in warm to hot weather, and very rarely when dogs are in extremely stressful situations where they experience extreme fear or anxiety.

When a dog's temperature begins to rise the body continues to send blood to the outside of the body even to the point of depriving the inner organs of proper blood flow.  This leads to all sorts of internal organ damage including acute kidney failure, liver failure, stomach and intestinal ulceration, stomach and intestinal tissue death, and brain / nerve damage.  Once the body's temperature reaches 109 degrees, cell membranes start to break down, proteins start to denature, and organ failure is beginning to occur.  Few dogs that reach this stage ever recover.

Once the cells start to break down and proteins start to denature all sorts of things start to go wrong.  The cells and proteins that are responsible for clotting the blood start to form clots everywhere leading to blocked blood vessels and loss of even more blood to internal organs.  Once all the clotting cells and proteins are "used up" then the animal is unable to keep from bleeding as its blood vessels start to break down from the effects of the high heat (via disrupting cells that line the blood vessels).  Nerve tissue is very susceptible to heat injury and often permanent damage is done to the cells in the brain and spine leading to seizures, coma, and death.   The poor heart is trying its best to cool the body and keep blood going to the organs and as more and more blood leaks out of the damaged vessels its job becomes even more impossible.  To make matters worse as the tissue in the stomach and intestine dies from lack of blood flow and the effects of the high temperatures, bacteria that normally reside in the gut can now "break in" to the body resulting in a septicemia and endotoxemia which further injures the blood vessels and organs.

Animals with heat stroke present with signs ranging from increased heart rates, excessive panting, increased salivation, and dehydration; to shock, respiratory distress, hemorrhage, vomiting frank blood, and diarrhea with
digested or frank blood; to seizures, stupor, coma, cardiac arrest, and respiratory arrest; to death.

Treatment is to cool the animal as quickly as possible but to not overcool them as this will result in shock as well.  Ice is the obvious choice to cool the animal but some studies suggest that ice works too well in that is constricts blood vessels in the skin preventing heat loss from the internal parts of the body and actually slowing heat loss.

Actions for the owner include:

• Pour cool water all over the dog and place the dog in front of a fan (increase evaporation)
• Rubbing alcohol on the stomach, foot pads, and ears (for evaporation)
• Getting the animal out of the heat into the shade or air conditioning
• Cool water immersion (as in a bath tub - again avoid ice for the reason mentioned above)
• Placing cool compresses on the inside of the thighs and the shoulders where large arteries run below relatively little fur and, thus, can give heat to the compresses without a fur coat in the way
• Getting the animal to a veterinarian as soon as possible.

The veterinarian can give cool intravenous fluids, cool enemas, and in emergency situations open the abdomen and wash the abdominal organs in cool, sterile fluid.

Whenever the cooling treatment is begun either by the owner or the veterinarian, the dog's temperature should be monitored, if not constantly, then every 3-5 minutes.  Stop cooling the animal when its temperature reaches 103 degrees or you risk sending the dog into hypothermia (i.e. too low a body temperature which can be fatal also).   Usually, the temperature will continue to drop past the 103 degrees.  Once the elevated temperature has been returned to a more normal level, treat the remaining problems and wait to see what will resolve and what is permanent damage.

Prevention is obviously the best medicine in this case.  Don't leave your dog in the car during the summer even for a "few minutes."  Be sure your pets have plenty of shade and water.  Don't allow your dogs to exert themselves excessively in hot weather.  Keep dogs with predisposing conditions like laryngeal paralysis cool and quiet.  Keep short nosed breeds like Bulldogs and Boxers cool and quiet as well.

Heat exhaustion is a mild form of heat stroke in which the body does not reach such a critical state but damage is done resulting in a weak, lethargic animal that has trouble doing anything for days to weeks.  Usually the dog will fully recover but it takes time.

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