When hot is TOO HOT!
June 18, 2015
From the desk of Dr. Voorheis
As I sat and thought of what topic to write about next, I went outside to put my feet in the pool because I was hot. Devine inspiration struck and I thought I would write about heat stroke in dogs and cats. You may remember seeing something on the news recently about a Boxer suffering from heat stroke up in Runyon Canyon. The owner had taken the dog out for a hike in the heat of the late morning and the Boxer was unable to keep up in high temperatures. First aid was rendered to the dog by LA County Fire who was thankfully nearby at the time. Heat stroke in animals is very serious. You see, they do not have the same ability that you and I have to self cool. They cannot sweat.
Heat stroke is defined as a body temperature between 106 and 109, which results in thermal injury to tissues. Our bodies are not made to reach those temperatures, and bad things happen to tissues when those temperatures are reached. As we move into the summer, it is appropriate to talk about heat stroke because we see it quite a bit. Every year that I have been a veterinarian, I have seen cases of heat stroke. What are the risk factors for heat stroke? Any breed prone to upper airway obstruction, for example brachycephalic breeds (Pugs, French Bulldogs, Bulldogs, American Bulldogs, Boston Terriers, Pit Bulls, Boxers, and Mastiffs etc) or the breeds prone to laryngeal paralysis (Labrador Retrievers, Golden Retrievers and others). Obesity is also a risk factor. Dogs and cats confined in non-ventilated areas, deprived of water or shade, subjected to forced heat (such as dryers after bathing), locked in cars etc. I’ve had cats crawl into clothes dryers. One of the more common presenting scenarios is the brachycephalic breed that is taken for a run in the late morning to early afternoon. The owner not realizing his dog cannot cool himself. I’ve seen the same scenario with a lab being taken for a run during the day, with owner not realizing that the loud breathing his dog has prevents him from cooling.
So how does this happen? How do we normally keep cool? To put it simply, thermoregulation is controlled by the brain (thermoregulatory center is in the anterior hypothalamus). Core body temperature is kept mostly constant in the normal dog and cat, under usual temperature fluctuations. Elevated ambient temperatures stimulate panting, drooling of saliva and vasodilation which cool the body by evaporation and radiation. In people, I would have added sweating as a major means of keeping cool. We sweat, the sweat cools on our skin, and it’s one of our ways to keep cool. Dogs and cats don’t sweat. The sweat glands are only found on the nasal planum and the foot pads. This is not enough to keep cool.
Abnormal ambient temperature and humidity make it difficult for the normal means of temperature control to function. Translation: Hot, humid weather is the worst for dogs and cats.
In the early stages of heat stroke, cardiac output increases due to peripheral vasodilation and decreased vascular resistance. As hyperthermia progresses, blood pools in the blood vessels supplying the GI tract and other abdominal organs, this causes a decrease in blood returning to the heart, a decreased circulating blood volume resulting in LOW BLOOD PRESSURE. Cardiac output declines, decreasing further circulating blood volume, the heat loss that was happening through radiation and convection fails and heat stroke worsens.
Initially, as dogs or cats pant, they develop something called respiratory alkalosis which means they blow off carbon dioxide and their body pH elevates. Then with the hypotension that develops, they develop metabolic acidosis. The bottom line is fluctuations in body pH that are dangerous require life saving intervention. As temperatures elevate, body proteins denature (break down), the enzymatic reactions that are essential for life stop happening and tissue death ensues (this is called necrosis).
All of that is happening at a cellular level. At the organ level, we see acute renal failure from direct thermal damage and from poor renal blood flow. Muscles breakdown and those large muscle proteins contribute to acute renal failure. In the gastrointestinal tract, direct thermal damage happens to the cells lining the gut and from poor GI blood flow – these cells rapidly die, resulting in hemorrhagic diarrhea. The toxins that are present in the gut and the bacteria that live in the gut cross into the bloodstream and cause sepsis, endotoxemia and SIRS (sudden inflammatory response syndrome). The brain swells and infarction (stroke) occurs. The same damage described above as happening in the kidneys and gut also happens in the liver and the heart. Bottom line – there isn’t an organ that heatstroke doesn’t affect negatively. That is why there is more than a 50% death rate from heatstroke in dogs and cats.
Treatment is cooling; cool water in a tub or garden hose, then transport to hospital. If hospital is close, just transport. Cool water is better than ice water. Treatment is IV fluids, colloids, plasma, and treating individuals as their signs dictate. The prognosis is usually guarded.
Prevention is easier than treatment. Be aware if you have a high risk dog or cat and take extra precautions. I’m gonna jump on my soap box here. If your dog is obese, work on weight loss. If you walk your dog (and you should) do so before 9 am in the summer time. If we are having hot humid weather, take precautions. Provide access to shade and water. Owners of brachycephalic breeds – these lovable dogs walk around at risk every day. It does not take much for them to overheat. So keep them thin and keep them cool. Owners of older labs, goldens and other large breed dogs should take the same precautions. If they are “loud breathers” walking around the house, there is a good chance they have laryngeal paralysis. Talk to one of us about laryngeal paralysis. These guys don’t cool well either. It goes without saying (but I will say it). Don’t leave your dog or cat in the car. Not even for a few minutes. You will live to regret it. They might not live through it. Don’t mean to scare you too much… but this is very real. We all see it on the news every summer and all over the internet and social media. Be aware and take precautions. They depend on you for their safety and well being. As always, if you have questions or concerns about your critters, we are here to help. Never hesitate to give us a call.
Until next time,