Summer is a great time to be a dog owner. Long warm days mean plenty of outdoor activities like swimming, hiking, and playing. It’s important to remember however, that just like us, our canine friends can overheat. As a result, taking precautions in the spring and summer is critical. With attention to your dog’s behavior in the heat and preparation for the season, you can avoid a heat stroke.
What Causes Heat Stroke?
The canine body operates best in a very narrow temperature range – usually from 99 to 102 degrees. Above 109, and body systems will become severely damaged.
The dog’s temperature is tightly controlled by the hypothalamus, an area in the brain. Elevations in temperature can be caused either by endogenous factors (inside the body) or exogenous (outside).
Fever occurs when the hypothalamus resets the normal body temperature higher as a result of infection or inflammation. It is initially a beneficial response, as it enhances the ability of the immune system to destroy viruses and bacteria. With fever, trying to cool a dog down will not help, as the brain is controlling the body temperature. It will only lead to shivering as the body tries to rewarm to the new set point. This is uncomfortable and expends energy. Cooling is not recommended for fevers.
Heat stroke (hyperthermia) is caused by external factors such as a hot environment or overexertion in the heat. The brain set temperature is normal, but a dog is unable to cool effectively, and so body temperature rises.
Dogs cool by two mechanisms: evaporation and conduction. Evaporation of heat occurs with heavy panting. Conduction occurs when a hot dog lies on a cool surface and heat is transferred. Dogs sweat very minimally and only through their footpads, so this is not a significant means of cooling.
Heat stroke progresses through three stages. It begins with heat stress. Initially, a dog will pant heavily, seek a cool surface, and drink water to bring body temperature down.
If a dog cannot do these things or cannot do them effectively (such as when trapped in a hot car), heat stress develops into heat exhaustion. The panting becomes much faster, heart rate elevates, the gums become red and tacky, and body temperature is likely greater than 106 degrees.
If this goes unaddressed, heat stroke develops. Body temperature exceeds 109 degrees. A dog will vomit, have profuse diarrhea, begin to seizure, and collapse.
Most Susceptible Dogs
All dogs can have heat strokes, but some are more prone to developing problems. Brachycephalic breeds like Bulldogs, Boston Terriers, and Boxers are notorious for overheating. Due to breed-related airway abnormalities such as small nostrils, long floppy palates and tonsils, and narrow, weak windpipes, brachycephalic dogs can overheat very quickly.
However, Labradors and other breeds vulnerable to laryngeal paralysis, another obstructive upper airway disease, are also at significantly increased risk. Dogs with cardiac disease can be predisposed, as well.
Another consideration is whether a dog is conditioned enough to be in the heat. Dogs who are not accustomed to exercise and exert themselves in hot weather can suffer heat stroke very rapidly. This is especially true if they are overweight or elderly.
Most commonly, any dog left in an unventilated car in temperatures above 65 degrees can suffer from heat stroke. This is most often seen in the spring and summer.
Heat stroke is not immediate. Symptoms begin with heavy panting and restlessness. This progresses to weakness and collapse, followed by profuse vomiting and diarrhea (often bloody). As heat stroke continues, a dog will become extremely dull to non-responsive. Seizures can develop in the late stages. Red to purple spots and patches may become visible on the skin.
Once the heat stroke goes untreated, every body system becomes involved. Shock develops. This means decreased oxygen delivery to tissue, which eventually leads to multiple organ dysfunction syndrome (MODS).
In the kidneys, the renal tubules (responsible for conserving water and electrolytes) are damaged. Water, glucose, and electrolytes are lost instead of conserved. Potassium, instead of being excreted, is retained. High levels of potassium causes cardiac arrhythmias.
The ability to clot blood is also severely affected. Coagulation proteins are made in the liver, and they function within the body’s normal temperature range. At above 109 degrees, they are damaged, and clotting becomes difficult. This leads to visible bruising on the skin called petechiae. When these coalesce into large patches, they are called ecchymoses. It is especially visible on the belly, where there is less hair, on the gums, the white of the eye (sclera), and inside the ear pinna.
Liver damage also occurs due to shock. The liver is essential for many functions. Two of the most important are production and storage of glucose, the body’s energy source, and the manufacture of clotting factors. Most dogs suffering heat stroke will have low blood glucose levels due to liver damage. Brain tissue is likewise affected leading to swelling of neurons. This can cause stupor, seizures, coma, and death.
The cells lining the gastrointestinal tract start to die as a result of the hyperthermia. Once those cells are damaged, the protective lining of the intestines weakens and thins, leading to bacteria moving freely into the bloodstream (bacterial translocation). This causes “blood poisoning” or sepsis.
Every system of the body feels the effects of heat stroke, making prompt care imperative to recovery.
Treatment of true heat stroke must be rapid and aggressive. Immediately cool your dog if you suspect heat exhaustion. If you have a hose or bathtub, wet your dog down with cold water thoroughly, especially the paw pads and thinly haired areas like the stomach (this will help dissipate heat quicker). If you are outdoors and near a body of water, a quick dip can help bring down temperature.
After cooling, take your dog to the veterinarian. Do not wait to see if he improves, as heat stroke can be deadly in a matter of hours.
Heat stroke causes shock, and this must be treated quickly. Initial vitals will be taken while the veterinary team works to stabilize your dog. If you have already cooled your dog at home, the temperature may be lower than expected, but this does not mean your dog has not had a heat stroke.
An intravenous (IV) catheter will be placed, and cool fluids will be given rapidly. This will increase blood flow to all parts of the body and improve oxygen delivery. Fans and cold water will be applied to bring body temperature down. Oxygen should be supplied either via face mask or nasal prongs. Ice chips in the oxygen mask can cool and moisten the air to further increase cooling.
Additional treatments should include broad spectrum antibiotics to protect against bacterial translocation and sepsis, IV dextrose to maintain normal blood sugar levels, mannitol or hypertonic saline to decrease cerebral edema (swelling in the brain), and continued oxygen and IV fluids. Fresh frozen plasma may be given in cases where clotting abnormalities have already developed. The plasma can provide clotting factors when the liver cannot manufacture its own or when they are deactivated by hyperthermia.
The prognosis is always guarded, as uncontrolled hyperthermia leads to multiple organ damage. Immediate, intensive care will improve the prognosis. Hospitalization can be prolonged, often at least 48 to 72 hours. During that time, frequent vitals and bloodwork should be conducted, including tests of clotting times and blood glucose.
Avoiding Heat Stroke
When the weather warms up, it is important to slowly acclimate your canine companion to the weather. Heat and humidity both play a role in overheating, and even on moderately warm days, if the humidity is high, overheating can occur. Plan exercise and activities for the cooler parts of the day – around sunset and early in the morning. If the temperature is moderately hot, your dog can spend short periods of time outdoors to acclimate. Do not exercise an unconditioned dog in the heat.
Any dog with upper airway abnormalities or cardiac disease should have minimal outdoor time in the summer. At the first sign of any overheating, they should be calmed and aggressively cooled with a hose or bath. This includes brachycephalic breeds and dogs with laryngeal paralysis and heart disease.
Make sure when your dog is outside that he has shade and plentiful fresh water. Keeping it cold and fresh may encourage your dog to drink more. Replenish frequently and add ice cubes. A kiddie pool filled with cold water is also excellent for the water-loving canines. If you plan to visit a dog park, choose one that has water nearby for swimming and playing.
There are an array of cooling devices that can be found for purchase including vests, sleeping pads, dog houses, and collars. (The best of these were recommended in “How to Prevent Heat Stroke in Dogs,” in the July 2015 issue.)
The best tip to remember is, if you’re in doubt, err on the side of caution and avoid overdoing it!
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