Article by Dr. Debra Primovic
Canine heat stroke is a condition arising from extremely high body temperature (rectal temperature of 105 to 110 degrees Fahrenheit), which leads to nervous system abnormalities that may include lethargy, weakness, collapse or coma. Abnormally high body temperature (also called hyperthermia) develops after increased muscular activity with impaired ability to give off heat due to high heat and humidity or respiratory obstruction. Allowing a dog to remain in a car with closed windows on a hot summer day is probably the most common cause of heat stroke.
Normal dogs dissipate heat from their skin. In addition, panting allows evaporation of water from the respiratory tract and is an effective method of heat dissipation. When these mechanisms are overwhelmed, hyperthermia and heat stroke usually develop. The elevation in body temperature stimulates the body to release substances that activate inflammation.
At temperatures greater than 109 Fahrenheit, failure of vital organs, and consequently death, occurs.
Heat-related illnesses, including heat stroke, heat exhaustion and heat cramps can occur after exposure to extremely high environmental temperatures. These illnesses occur in all mammals and can be prevented by taking proper precautions.
Animals at greatest risk for heat-related illness include:
# Puppies up to 6 months of age
# Overweight dogs
# Dogs overexerted during exercise
# Dogs that are ill or receiving certain medications
# Brachycephalic breeds (dogs with short, wide heads like pugs, English bulldogs, Boston terriers)
# Dogs with obstructive airway diseases
# Dogs with pre-existing fever
# Dogs that are dehydrated
# Dogs with heart disease
# Dogs with poor circulation due to cardiovascular or other underlying disease
# Older pets (large breed dogs over 7 years of age, small breed dogs over 14 years of age)
# Pets with a history of seizures
# Pregnancy and nursing
What to Watch For:
# Noisy breathing that may indicate upper airway obstruction
# Excessive panting
# Bright red mucous membranes (gums, conjunctiva of the eyes)
# Altered mentation
# Petechiae (pinpoint hemorrhages on the gums and/or skin)
Certain tests are needed to confirm the diagnosis of heat stroke and exclude other diseases that may cause similar symptoms or to better understand the impact of heat stroke. These tests insure optimal medical care and are selected on a case-by-case basis. Your veterinarian will take a complete medical history and perform a thorough physical examination. A complete medical history and thorough physical examination, including rectal temperature.
Diagnostic tests are needed to diagnose heat stroke and assess the extent of vital organ dysfunction, including:
# A complete blood count (CBC or hemogram) or packed cell volume or PCV. This is a simple test to evaluate your dog for the presence of blood loss (anemia), to assess the severity of dehydration and cardiovascular stress, low platelet concentration, or inflammation. It determines the percentage of the blood occupied by red blood cells, which is normally 35 to 55 percent in dogs. Total plasma protein concentration (TP) evaluates the hydration status (water will be lost from the blood during dehydration resulting in a higher concentration of proteins in blood).
# Tests of coagulation including: activated coagulation time (ACT); prothrombin time (OSPT); partial thromboplastin time (APTT); serum fibrinogen concentration; and platelet count. Fibrin degradation products (FDPs) to evaluate and to identify the presence of a life-threatening, body-wide disorder called disseminated intravascular coagulation (DIC). This is the failure of blood clotting which can result in consumption of the body’s clotting proteins and ultimately the inability of the blood to clot that is often a complication of heat stroke. The presence of breakdown products of fibrin (called fibrin degradation products) indicates that fibrin (the active form of the blood clotting protein fibrinogen) has been broken down and can serve as an important clue and supports the diagnosis of DIC.
# Serum biochemistry tests to assess the extent of damage to vital organs such as muscles, kidneys and liver. To evaluate kidney function since acute kidney failure can complicate heat stroke, there is Blood urea nitrogen (BUN), serum creatinine concentrations, and serum phosphorus concentrations. For liver function – alanine aminotransferase, aspartate aminotransferase, and alkaline phosphatase. And for muscle function – creatine kinase.
Blood glucose and electrolyte (sodium, potassium, chloride) concentrations to evaluate for body wide infection (sepsis), the electrolyte and acid base status, and metabolic abnormalities that can complicate heat stroke.
Blood gas analysis may show abnormalities in body wide acid base balance including metabolic acidosis due to poor circulation and kidney failure or respiratory alkalosis from excessively rapid breathing.
# Routine urinalysis to identify leakage of protein including the muscle protein myoglobin, which can damage the kidneys and cause acute kidney failure. Damaged kidney cells may be sloughed into the kidney tubules and form microscopic casts that indicate ongoing damage to the kidneys.
# An electrocardiogram (ECG or EKG) may be recommended if arrhythmias are suspected. Arrhythmias are a relatively common complication of heat stroke.
Intensity of treatment must be individualized and based upon the cause and severity of the heat illness, the condition, complications, pre-existing health problems, and other factors that must be analyzed by your veterinarian. Treatments may include:
# For mildly increased temperature (rectal temperature of more than 102.5 F but less than 105 F) your dog may only require rest, a fan to increase air circulation, fresh water to drink and VERY careful observation. If the dog worsens or the temperature increases then medical attention is indicated.
# With temperatures between 105 to 107 F, hospitalization and aggressive medical therapy likely will be recommended. If complications (arrhythmias, kidney failure, liver failure, gastrointestinal bleeding, cerebral edema, and/or disseminated intravascular coagulation) have occurred, the following additional treatments will be necessary.
# Dogs with markedly increased temperature (greater than 107 F) must be treated aggressively.
Cooling can be accomplished externally with cool water baths, application of alcohol to the footpads, enhanced air circulation using a fan, and careful placement of ice packs over areas with large superficial blood vessels (neck, groin, armpit). Internal cooling methods include intravenous administration cool electrolyte solutions, cool water enemas, lavage of the stomach with cool water, or rarely necessary -peritoneal dialysis with cool electrolyte solutions (instillation of cool electrolyte solutions into the peritoneal cavity by means of a catheter).
# Underlying conditions, such as heart disease, respiratory disease and dehydration should be treated with appropriate medications, oxygen delivery, and intravenous administration of electrolyte solutions. Fluid therapy is often started immediately to treat the shock and metabolic waste concentrations that may accompany heat stroke.
# Close monitoring of your dog is necessary to guide treatment. You and your veterinarian will have to evaluate your dog’s rectal temperature, heart rate and rhythm, respiratory rate, blood pressure, urine output, level of consciousness, pinpoint hemorrhages on the gums or bruising of the skin, vomiting, diarrhea or gastrointestinal bleeding.
# The anti-clotting medication heparin may be recommended to prevent disseminated intravascular coagulation (DIC) or if your dog is in the early stages of this life-threatening complication. Plasma that has been frozen soon after collection (fresh frozen plasma) may be administered to provide clotting factors in cases of DIC after your pet has been treated with heparin to prevent ongoing coagulation. Sometimes heparin is mixed in with the fresh frozen plasma.
# Mannitol may be used to reduce cerebral edema if it is suspected.
# The drugs dopamine and furosemide may be used to dilate blood vessels to the kidneys and to increase urinary excretion of salt and water, respectively. These treatments are given when acute kidney failure due to heat stroke is suspected.
# Sucralfate is a coating agent that can be used to limit gastrointestinal bleeding. Cimetidine and omeprazole are drugs that can be used to decrease acid secretion by the stomach and reduce the risk of gastrointestinal bleeding.
# Antibiotics may be administered to treat suspected bacterial infection.
# Dextrose (sugar) may be added to your dog’s intravenous electrolyte solution to prevent or treat low blood sugar concentration (hypoglycemia).
# The short-acting anti-convulsant agent diazepam may be recommended for seizures. Other seizure medications such as Phenobarbital may also be needed if diazepam is ineffective.
# The anti-arrhythmic agent lidocaine may be used to treat certain heart rhythm disturbances (rapid ventricular tachycardia).
The need for additional treatments depends on the severity of heat stroke and secondary complications that may arise. Complications of heat stroke may include:
# Disseminated intravascular coagulation (DIC)
# Liver failure
# Acute kidney failure
# Muscle breakdown
# Low blood pressure (hypotension)
# Low blood sugar (hypoglycemia)
# Convulsions (seizures)
# Secondary infections (including pneumonia)
# Gastrointestinal problems including bleeding and absorption of bacteria or toxins from the intestine with development of systemic infection (sepsis)
Home Care and Prevention
Heat stroke is a life-threatening emergency. Check your dog’s temperature rectally if you suspect heatstroke. Normal body temperature in dogs is higher than in humans (99.5 to 102.5 F as compared to 98.6 F). If your dog’s temperature is over 105 F, call your veterinarian and remove your dog from the heat source immediately.
Meanwhile, place a cool, wet towel over your dog or place him in a cool water bath. Do NOT use ice because it may cause skin injury and causes surface vessels to constrict preventing cooling of core organs and tissues. Surface blood vessels should remain dialated to carry core body heat to the body surface via circulation of blood and lymph so the body temperature can decrease.
There are several things you can do to prevent heat related problems for your dog:
# Monitor outdoor temperature and minimize your dog’s activity and provide cool housing on hot, humid days.
# Limit sun exposure during the hours of 11 AM to 3 PM on hot days.
# Walk or exercise your dog in the morning or evening when it is cooler or if temperatures are high limit exercise.
# Keep your dog in a comfortable environment (air-conditioned room, partially open windows with a breeze, fans, shade, etc ) during extremely hot weather.
# NEVER leave your dog in a car (even with the windows partially rolled down) for any reason at any time. Leaving dogs in a car during warm weather is the most common cause of heat stroke.
# Provide your dog with plenty of fresh water and plenty of shade. Take extra care with puppies, thick coated or long haired dark colored pets with medical problems, obese pets and senior pets.
# If possible, allow your dog to acclimate gradually to high temperatures. Heat illness is common in the spring when the animal has not had sufficient time to acclimate to the warmer temperatures.
# After traveling to a warmer climate, allow your dog several days to become acclimated before allowing any vigorous exercise.
# Consider the length of coat, amount and thickness of hair, and coat color when evaluating the amount of exercise and environment that is safe for your dog when the weather is warm and hot.
# Supervise children as they play with dogs in hot weather and prevent them from exercising or housing dogs to risk heat strokes. Children often can not understand that dogs will get hotter faster and can not cool down in comparason to themselves.
# Prevent dogs from “denning up” in places where they can not get out to a cooler area.
# Do not encourage or allow dogs to engage in activities that they have instinctive drive to persue that will interfere with their sense of discomfort or danger ( i.e. hunting, retreiving, herding, digging, etc)
Other medical problems can lead to symptoms similar to those encountered in heat stroke. These conditions should be excluded before establishing a definitive diagnosis of heat stroke:
# Anxiety and fear
# Drug intoxication causing hyperactivity or seizures
# Intense exercise
# Hyperthyroidism (overactivity of the thyroid gland)
# Hypoglycemia (low blood sugar concentration) resulting in seizures
# Hypocalcemia (low blood calcium concentration) resulting in increased muscle activity or seizures)
# Malignant hyperthermia (greatly increased body temperature) during anesthesia
# Abnormality of the temperature regulation center in the hypothalamus of the brain
# Seizures of any cause
The prognosis is variable. The prognosis depends on the severity of the clinical signs, response to treatment and secondary complications. Pets that are extremely mentally depressed or that have active signs of hemorrhage have a poorer prognosis.
Optimal treatment for your dog requires a combination of home and professional veterinary care. Follow-up is crucial. Administer any medications prescribed by your veterinarian and contact your veterinarian if you are experiencing problems treating your dog.
Observe your dog’s activity level and appetite. Monitor his skin for bruising and gums for pinpoint hemorrhages.
Your dog should be re-examined after 3 to 7 days to evaluate serum biochemical tests and an electrocardiogram (ECG or EKG) if arrhythmias were detected during hospitalization.
The actual follow-up procedure employed will depend on the severity of your dog’s heat illness, his response to therapy, and your veterinarian’s recommendations.