Heat Stroke

Heat stroke occurs when the dog's ability to regulate its body temperature is lost.  A dog regulates body temperature primarily through respiration.  When the respiratory tract cannot evacuate heat quickly enough, the body temperature rises.  Normal body temperature is less than 103F, but once the temperature goes over 105F a number of physiologic events can occur that make it even more difficult for the animal to regain control of its temperature.  At this time, oxygen delivery to the system cannot keep up with rapidly elevating demand.  If the temperature exceeds 108F, cellular damage starts to occur in a number of organ systems including the kidneys, liver, gastrointestinal tract, heart and brain.  The extent of the cellular damage depends on the magnitude and the duration of the temperature elevation.  Clearly, this can be a life-threatening situation, but for those animals that survive there is the possibility of long term problems after the occurrence. 

There are a number of predisposing factors for heat stroke.  Some of the most significant are listed here:

Heat 
Humidity 
Muscular activity 
High body mass 
Anxiety 
Poor ventilation 
Dehydration 
Obesity 
Antihistamines 
Phenothiazines (some medications for vomiting) 
Brachycephalic breeds (short-nosed breeds) 
Increased age 

Dogs experiencing heat stroke will have a muddy pink colour of their gums instead of the nice red-pink colour that normally exists.  Their heart rate will be dramatically elevated, and they will be panting furiously.  They tend to stand or walk very slowly without regard to where they are.  Some will lay on their sternum.  Most dogs will have a wild or panicked expression and are not particularly aware of their environment.  Any combination of these symptoms should have an owner scrambling for a rectal thermometer and taking those steps necessary to help drive the temperature back down.  If a thermometer is not available, presume it to be heat stroke and initiate treatment.  If the animal does not respond favourably, the diagnosis can be re-evaluated later.  Significantly delaying the treatment of heat stroke can dramatically increase the risk of long-term consequences or death. 

Heat stroke is an emergency that requires veterinary assistance, but you can effectively initiate treatment in most cases before heading for the veterinary hospital.  You must aggressively assist the dog's efforts to lower body temperature with the use of water and air.  Since the lungs cannot keep up with the heat build-up, we now have to cool the skin and associated blood vessels so the body's temperature will decrease.  Submersion of the dog in cool water will start to bring the temperature down quickly.  You will want to avoid extremely cold water or ice since they cause the blood vessels in the skin to constrict and will not allow for a meaningful heat exchange.  If there isn't anything available to submerse the dog in, you can start wetting him down with a hose.  Wet him down all over, but let the water run continuously in the groin area since there are large numbers of significant and relatively superficial blood vessels in that area that will allow for more rapid cooling of the blood.  The dog should be in a well-ventilated, shady area to allow for evaporation of the water.  Evaporation cools body temperatures very effectively.  When you are transporting him to the veterinary hospital, keep the air conditioner on or the windows open, or use the back of a truck to increase evaporation.  Do not use an enclosed style crate since it allows for very little evaporation or fresh cool air for the lungs.  Do not cover the dog with a wet towel as it will prevent evaporation. 

Once the temperature starts dropping, you should seek veterinary assistance.  It is advisable in most cases to start these animals on intravenous fluids and monitor kidney and liver function for at least several days.  The necessity for this laboratory work depends on the magnitude and the duration of the elevated temperature, but even in relatively short mild occurrences, it is a wise precaution to take. 

Obviously prevention of heat stroke is a far better alternative than treatment.  Everyone is aware of the risks of having a dog in a vehicle in the summer, but there are some less obvious risk factors that we all need to be aware of.  Even moderate environmental temperatures can be very significant when there is little or no ventilation.  Heavy muscular activity drives body temperatures up with alarming speed.  Following intervals of high activity, return the dog to an air conditioned vehicle, or wet the dog down and go to an area that is shaded and preferably breezy to allow for evaporation.  Do not wet the dog down and return it to an enclosed style crate, as you will be creating a steam bath like environment.  Make sure there is access to reasonable volumes of cool fresh water both before and after activity. We also need to be conscious of those animals that are at increased risk, which would include those dogs that have high body mass, older dogs, and those that are carrying more weight than is normal for them.  Being aware of the various risk factors as well as the environmental considerations should help all of us avoid this potentially devastating problem.
 

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