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Heat stroke is hyperthermia/high body temperature that develops when the body’s normal cooling mechanisms (mainly panting) are overcome by heat. The body temperatures in these animals are often 106° F and above. The problem with such high body temperatures is the development of multisystemic organ damage and dysfunction. Both dogs and cats of any age or breed can be affected. Obese animals and those with thick hair coats are at an increased risk. The brachycephalic/shortnosed dog breeds (including bulldogs, pugs, shih tzus, lhasa apsos, etc.) are especially predisposed due to breed related upper airway conformation that limits efficient heat dissipation through panting. Dogs with laryngeal paralysis are also predisposed. Humidity and enclosed spaces with poor ventilation (cars without the windows down) predispose by decreasing the efficiency of heat dissipation from the body. Thus, a humid day, even if it is not particularly sunny, can precipitate heat stroke just as easily as a 100° sunny day. And animals shut in cars without the windows down can suffer from heat stroke even on a cool day.

Signs of heat stroke are varied and include heavy panting, increased noise while breathing (wheezing type sounds), upper airway obstruction (especially brachycephalic dog breeds), drooling, bright red gum color, red-purple splotching on the skin or gums (petechia), shaking, dull mentation, seizures, vomiting, diarrhea, collapse, shock, coma and sudden death. Diagnosis is based on known exposure to heat/humidity/poorly ventilated environment, hyperthermia where true fever (high body temperature from the body’s response to an inflammatory process) is ruled out and clinical signs.

It is important for a full work-up to be done on the animal to rule out inflammatory diseases that may be causing fever and to identify the sequella of heat stroke. Any organ(s) can be damaged and stop functioning properly with heat stroke. Cerebral edema or swelling in the brain, liver damage, acute kidney failure, heart arrhythmias, gastrointestinal ulceration and blood clotting abnormalities are probably the most common sequella we see. A CBC, biochemistry screen, urinalysis and coagulation screen are often the baseline diagnostics performed and are often repeated regularly to monitor progression. Chest x-rays are recommended for some patients, especially those that present with severe upper respiratory compromise, as fluid accumulation in the lungs (pulmonary edema) can be a sequella.

Hospitalization of patients with heat stroke is imperative. Most animals require intensive care and monitoring for a couple of days. Initial treatment involves cooling the patient relatively aggressively, oxygen support and IV fluids. Some patients with severe upper respiratory compromise require a tube placed in the trachea to breathe through. Sedation may be necessary to keep very anxious/hyperactive animals quiet and cool. Broad-spectrum IV antibiotics and GI protectants are indicated in most cases. Other specific medications will be used based on the signs/sequella that arise (i.e. antiseizure medications, anti-arrhythmics). Blood pressure, ECG and urine output monitoring is important.

The prognosis for heat stroke is guarded in general and very variable between patients. The severity of the hyperthermia, duration of hyperthermia and presence of predisposing factors all lend toward the likelihood/severity of multiorgan damage and thus overall prognosis. Sometimes organ damage is repairable with time, but sometimes it is not. Unfortunately, there is no reliable way to determine which patients will recover fully and which will not at initial presentation. Some patients recover and are discharged from the hospital but develop later sequella, such as seizures or heart arrhythmias. Many times these things can be controlled, but it is important for owners to be aware that they can develop. Patients that develop a syndrome called DIC/disseminated intravascular coagulation, have a very poor prognosis. This is a very complex syndrome of altered blood clotting, bleeding and further organ damage that is very difficult to prevent and treat.

Above all the most important thing for owners to understand about heat stroke is that it is an emergency situation. The animal should be taken to a veterinarian as soon as possible for treatment. Cooling during transport with air conditioning and wet towels is a good idea, but delay in getting the animal to the hospital for cooling at home is not recommended. Aggressive care at a veterinary facility will give the best chance of full recovery, but owners must be aware of the possibility of complications and the guarded prognosis from the beginning.