Heat Stroke  
by PetPlace Veterinarians

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Overview

Heat stroke is a condition arising from extremely high body temperature (rectal temperature of 105° to 110°F), which leads to nervous system abnormalities (such as 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 heatstroke.

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. At temperatures greater than 109° F, failure of vital organs, and consequently death, can occur.

Heat-related illnesses, including heatstroke, 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
• Older pets (large breeds over 7 years of age, small breeds over 14 years of age)
• Overweight dogs
• Dogs that are overexerted during exercise
• Dogs that are ill or receiving certain medications
• Dog with short, wide heads (Brachycephalic), like Pugs, English bulldogs, Boston terriers
  Dogs with airway obstructive 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.

What to Watch for:

• Noisy breathing that may indicate upper airway obstruction
• Excessive panting
• Bright red mucous membranes (gums, conjunctiva of the eyes)
• Weakness
• Collapse
• Coma

Section 1 - Home Care

Heatstroke 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.

Section 2 - Preventative Care

There are several things you can do to prevent heat related problems for your dog:

• Monitor outdoor temperature and minimize your dog’s activity 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.
• Keep your dog in a comfortable environment (air-conditioned room or partially open windows with a breeze) 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 heatstroke.
• Provide your dog with plenty of fresh water and plenty of shade. Take extra care with puppies.
• 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 itself to the warmer temperatures.
• After traveling to a warmer climate, allow your dog several days to become acclimated before allowing any vigorous exercise.

Section 3 - Follow-up

Optimal treatment for your dog requires a combination of home and professional veterinary care. Follow-up is crucial. Be sure to:

1. Administer any medications prescribed by your veterinarian.
2. Contact your veterinarian if you are experiencing problems treating your dog.
   Observe your dog’s activity level and appetite.
3. Monitor your dog’s skin for bruising and gums for pinpoint hemorrhages.
   Re-evaluate after 3 to 7 days to evaluate serum biochemical tests and an 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.

Section 4 - Veterinary Care

Veterinary care should include diagnostic tests and subsequent treatment recommendations.

Diagnosis

Diagnostic tests are needed to diagnose heat stroke and assess the extent of vital organ dysfunction, including:

A complete medical history and thorough physical examination, including rectal temperature.

A complete blood count (CBC or hemogram) to assess the severity of dehydration and cardiovascular stress.

Tests of coagulation including: activated coagulation time (ACT); prothrombin time (OSPT); partial thromboplastin time (APTT); serum fibrinogen concentration; platelet count; and fibrin degradation products (FDPs) to identify the presence of disseminated intravascular coagulation (DIC), a life-threatening body-wide failure of blood clotting that is often a complication heatstroke. The presence of breakdown products of fibrin (called fibrin degradation products) can serve as an important clue to the presence of DIC.

Serum biochemistry tests to check blood glucose concentration, assess the extent of damage to vital organs, such as: muscles (serum creatine kinase test); kidneys (blood urea nitrogen and serum creatinine tests); and liver (alanine aminotransferase, aspartate aminotransferase and alkaline phosphatase tests) and to evaluate the electroyte and acid base status.

Treatment

Intensity of treatment depends upon the cause and severity of the heat illness.

Mildly increased temperature (less than 105°F) may only require rest, a fan to increase air circulation, fresh water to drink and careful observation.

Markedly increased temperature (greater than 106°F) must be treated more aggressively. Cooling can be promoted externally by immersion in cool water, or internally by administering a cool water enema.

Underlying aggravating conditions, such as upper airway obstructive diseases, heart disease, pulmonary disease, and dehydration may be treated with appropriate medications, supplemental oxygen or fluid therapy.

Treatment with cortisone-like drugs such as short-acting forms of dexamethasone or prednisone may be recommended.

The need for additional treatments depends on the severity of heatstroke and secondary complications that may arise. Complications of heatstroke may include:

• Disseminated intravascular coagulation (DIC).
• Gastrointestinal problems including bleeding and absorption of bacteria or toxins from the intestine with development of systemic infection (sepsis)
• Liver failure
• Acute kidney failure
• Muscle breakdown (called “rhabdomyolysis”)
• Low blood pressure (hypotension)
• Low blood sugar (hypoglycemia)
• Convulsions (seizures)
• Secondary infections (including pneumonia)

Section 5- Veterinary Care In-depth

Veterinary care should include diagnostic tests and subsequent treatment recommendations.

Diagnosis:

Certain tests are needed to confirm the diagnosis of heat stroke and exclude other diseases that may cause similar symptoms. Your veterinarian will take a complete medical history and perform a thorough physical examination. The following emergency tests may also be included:

Packed cell volume or PCV. This is a simple test to evaluate your dog for anemia. It determins 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).

Activated clotting time (ACT) to evaluate for a life-threatening, body-wide disorder called disseminated intravascular coagulation (DIC), which can result in consumption of the body’s clotting proteins and ultimately the inability of the blood to clot.

Blood urea nitrogen (BUN) and serum creatinine concentrations to evaluate kidney function since acute kidney failure can complicate heatstroke.

Blood glucose and electrolyte (sodium, potassium, chloride) concentrations to evaluate for body wide infection (sepsis) and metabolic abnormalities that can complicate heatstroke.

Additional Tests:

Your veterinarian may recommend additional diagnostic tests to exclude or diagnose other conditions or to better understand the impact of heatstroke. These tests insure optimal medical care and are selected on a case-by-case basis. Examples include:

Complete blood count (CBC or hemogram) to evaluate your dog’s hydration and to evaluate for the presence of blood loss, low platelet concentration or inflammation.

Serum biochemistry tests including tests of kidney function (blood urea nitrogen, serum creatinine and serum phosphorus concentrations), liver function (alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase) and muscle function (creatine kinase).

Specialized tests of clotting function including prothrombin time (OSPT), partial thromboplastin time (APTT), platelet count, fibrinogen, and fibrin degradation products to identify the presence of disseminated intravascular coagulation (DIC), which may complicate heatstroke. The presence of “fibrin degradation products” indicates that fibrin (the active form of the blood clotting protein fibrinogen) has been broken down and supports the diagnosis of disseminated intravascular coagulation (DIC).

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 heatstroke.

Treatment:

Treatment of heatstroke must be individualized and based on the severity of the condition and other factors that must be analyzed by your veterinarian.

Treatments may include:

If your dog has mild heat illness (rectal temperature of more than 102.5°F but less than 105°F), therapy may entail rest, increased air circulation using a fan, fresh water to drink and careful observation. With temperatures greater than 106°F, hospitalization and aggressive medical therapy likely will be recommended. If complications (arrhythmias, kidney failure, liver failure, gastrointestinal bleeding, disseminated intravascular coagulation) have occurred, additional treatments will be necessary.

Dogs with temperatures greater than 106°F should be treated more 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 peritoneal dialysis with cool electrolyte solutions (instillation of cool electrolyte solutions into the peritoneal cavity by means of a catheter). These methods are rarely necessary.

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 to treat the shock that may accompany heatstroke.

Treatment with short-acting cortisone-like drugs such as dexamethasone sodium phosphate or methylprednisolone sodium succinate may be recommended to combat shock.

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.

Other treatments may include:

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.

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 heatstroke 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).
Cortisone-like drugs (dexamethasone, prednisone) and oxygen therapy may be used if cerebral edema (accumulation of fluid in the brain) is suspected.
The short-acting anti-convulsant agent diazepam may be recommended for seizures.
The anti-arrhythmic agent lidocaine may be used to treat certain heart rhythm disturbances (rapid ventricular tachycardia).