Animals are probably more at risk from high temperatures and humidity than humans because we are better at losing excess heat from our bodies. People can dissipate body heat by sweating. Animals covered in fur cannot do this effectively and they have very few sweat glands; they dissipate heat by panting instead. This is not really as effective as sweating and the activity of panting may in itself produce extra heat and humidity, so animals are more vulnerable to conditions of high temperature and humidity than we are, (although humans may die from heat stroke too). People should remember that warm conditions which are reasonably comfortable for themselves may not be OK for their pet.
Dogs are commonly affected by heat stroke. Those animals most at risk are the brachycephalic breeds (short faced dogs such as the pug or bulldog), those with a thick hair coat, obese dogs, and the very young or the very old. Dogs with cardiovascular disease or other health problems may also be vulnerable. Heat stroke can develop very quickly indeed if the conditions are hot and humid.
It is impossible to write about heat stroke and not consider the effects of leaving dogs in cars. Almost everyone knows that they should never leave their dog in a parked car on a hot sunny day. If you consider how hot a parked car can get in the sun on such a day you will understand the problems a dog in the vehicle faces. Think about how uncomfortable it is to get back inside such a vehicle and how hot that steering wheel gets. Now imagine being locked in there and unable to wind down the window or open the door! It wouldn't be long before you felt unwell would it? Cars, even parked in the shade with a window open, act like greenhouses and get very hot, very quickly. The humidity inside the vehicle also builds up as the dog breathes then pants; this increases the animal's discomfort. As heat and humidity build up it becomes impossible for the heat control mechanisms of the body to work. Unfortunately it only takes a short time for these factors to cause serious hyperthermia (rise in body temperature). Many dogs die when left in cars!
It is not only dogs in cars which experience heat stroke. It could be the rabbit in a hutch which is left in the sun on a hot day. It could be the cat left in a carrier on the way to the boarding facility. It might be the hamster forgotten in the play ball. Dogs taken out around the park on a hot day may also succumb if they are not as fit as their owners or they have thick fur (the poor dog can't take his coat off!). As you can see there are numerous ways in which a pet can be overcome by the heat and suffer from heat stroke. It is up to us as responsible keepers to ensure that the conditions in which we keep our pets are comfortable and safe.
Now let's consider what happens in the body of an animal experiencing hot and humid conditions. The response of the animal feeling too warm will be to use various behavioural and physiological methods to lose heat and cool down in order to maintain its optimal body temperature. This is a homeostatic process.
Homeostasis is the scientific term for the regulation of the body temperature and other variables. If homeostatic regulation of the body temperature fails, the cells in the body will experience conditions in which they cannot function; this will lead to organ failure, collapse and death if not treated. Even with aggressive treatment heat stroke victims often die.
So how does heat stroke cause problems within the body? Living organisms are made up of cells. All cells contain proteins; these proteins may be part of the actual structure of the cell or they may have a particular function within the cell as enzymes (special proteins which take part in chemical reactions). One of the disadvantages of these proteins is that they will only function properly if the temperature is within a limited range. Beyond the optimal temperature for these proteins they can become denatured (their structure changes irreparably - think about cooking an egg; you are denaturing the proteins of the egg during this process; it's a serious change isn't it?) There are many chemical reactions going on in the cells of the body which will be adversely affected by a rise in temperature because the enzymes involved in these reactions will be denatured. Other cell proteins and the cell membrane can be denatured by high temperatures; this will ultimately lead to the breakdown of the cells. Once the cells of the body begin to break down there is a really serious problem. Since every organ in the body is composed of cells of one type or another, once cells start to die then the organs begin to fail. Organ failure will ultimately lead to death.
What are the signs of heat stroke?
Heat stroke in the dog makes him pant rapidly and intensely, he will become weak and stagger when he tries to walk, he will have staring, frightened eyes and will salivate profusely. If heat stroke progresses beyond this stage the dog eventually collapses and loses consciousness. The gums in these animals are pale and dry not a healthy pink (an indication of shock). If a vet takes the rectal temperature of the dog it will be very high 105F or above. (109F is the critical temperature for organ failure).
The organs and systems which may be affected by heat stroke include:
The liver - toxic thermal damage - liver failure.
The nervous system - damage to the actual neurons and cerebral oedema (swelling of the brain) - this may lead to seizures, coma and respiratory arrest.
The musculoskeletal system - damage of the muscles.
The kidneys - acute renal failure - the kidneys may not produce urine properly.
The heart - myocardial necrosis - damage to the heart muscle.
The gastrointestinal system - mucosal necrosis - can lead to toxins entering the blood stream.
The immune system and blood - the blood can become too thick due to dehydration and this can lead to disseminated intravascular coagulation - a serious condition involving multiple blood clots throughout the body.
The lungs - pulmonary oedema - this leads to breathing difficulties.
If you believe that your dog is suffering from heat stroke you should take him to your vet as quickly as you can; this is an emergency situation! On the way to the veterinary surgery you should try to cool your pet down. Spray him with cool water, have the fan in the car on cool or the windows open; if you have air conditioning it should be as cool as you can get it and on full blast. ( Cold ice baths are not recommended for heat stroke; they will make the surface blood vessels constrict and the dog may start to shiver, both of which reduce heat loss from the body).
Once your pet reaches the veterinary surgery your vet will continue to cool your pet down until the rectal temperature reaches about 103F. Dogs may sometimes receive oxygen. The dog may need treatment for complications associated with this condition so intravenous fluids and various drugs may be required. (Treatment will depend upon what complications are detected) . Your pet will probably need to be in the veterinary hospital for a while to receive treatment. The outcome for these pets is closely linked to the seriousness of the hyperthermia and the time taken to bring their temperature back to normal. In all cases the prognosis will be guarded to grave.
Do be aware that this is a life threatening condition and even with the best veterinary treatment your pet may die. Recovered animals may have neurological problems or damaged kidneys. If your dog has one episode of heat stroke he may be more vulnerable to having another, so take extra care with animals who have recovered from an episode of hyperthermia.
The best thing to do about heat stroke is to avoid it in the first place!
Never leave your dog in the car (If he can't go with you when you reach your destination leave him at home!)
Ensure your dog has access to water at all times during warm weather (dehydration makes the risk of heat stroke higher).
Don't keep your pet in an enclosed space where temperature and humidity can build up (outside rabbit hutches should be in a cool shady place preferably where they will get a light breeze in summer).
Avoid making your pet exercise during the heat of the day (walks will be more pleasant for both of you if you go in the cool of the early morning or in the evening).
Caged indoor pets should not be placed on the window sills.
Avoid taking your dog or cat abroad to a hotter climate than they are used to. If you must take them ensure they have time to acclimatize to the warmer environment.
Keep your pet at its optimum weight (obesity increases the risk of heat stroke).
Avoid taking your pet anywhere hot or humid.
If your dog has any kind of disease, but especially heart or respiratory problems, be aware that they may not be able to control their internal temperature as well as a healthy animal and take extra care with them.
If your pet is very young or old take extra care of them.
If your pet has a thick coat or is a very large breed they may be more vulnerable to heat stroke. Consider having their coats clipped in the summer months.
Allow your dog to use behavioural mechanisms to lose heat in hot weather. Your pet should be free to drink water, find shade, rest, and pant (so don't use a restrictive muzzle).
Remember that heat stroke is avoidable: it requires high humidity/ high temperatures and time for these to affect the body. If you take sensible measures to avoid these factors then the tragedies often associated with hyperthermia can be prevented.