Hyperthermia in Dogs

What is Hyperthermia in Dogs?

Hyperthermia is a general term for an abnormal increased body temperature. In dogs, the normal high-end temperature is 102.5-103 F. Dogs with temperatures above 103 F are considered hyperthermic. Increasing body temperatures, if they grow or remain high enough, can cause whole-body inflammation or blood-related issues such as coagulation complications, and this may lead to multi-organ failure.

Once a dog’s body temperature starts rising, regardless of cause, it is a life-threatening emergency. If a dog shows signs of hyperthermia, immediately contact an emergency veterinarian and start the following cooling process:

• Begin cooling your dog while on your way to a veterinarian.

• Soak the dog in water, especially around the groin, armpits, and neck.

• Do not use cold water or ice, because this can cause blood vessel constriction and delay cooling. Use lukewarm to cool water.

• Use car vents and fans to blow air on the dog.

• Offer small amounts of cool (not cold) drinking water.

• Do not submerge the dog’s head in water.

• Contact an emergency veterinarian to let them know you are on the way, and ask for any other instructions.

Depending on the cause, hyperthermia can progress rapidly, leading to life-altering permanent systemic damage, sometimes within minutes. Delaying veterinary treatment more than 90 minutes often results in a decreased survival rate. 

Symptoms of Hyperthermia in Dogs

Regardless of the cause, hyperthermia causes extreme damage to the body. Initially, dogs may seem distressed, pant, or be unsteady or restless. They may drool, or their gums may turn blue or bright red. As hyperthermia progresses, clinical signs include:

• Collapse

• Spontaneous bleeding

• Dehydration

• Seizures

• Extreme lethargy, progressing to a comatose state

Causes of Hyperthermia in Dogs

In general, hyperthermia has two causes:

• Infections (such as bacteria or viruses) trigger a fever, where the body’s core temperature rises as a response.

• External conditions, where other factors cause the body to increase in temperature. In this scenario, a dog’s body cannot dissipate the heat appropriately, so the body temperature continues to rise.

The most common external conditions causing hyperthermia include the following:

• Heatstroke often occurs when the temperature outside is high and there is a lack of good ventilation. This type of heatstroke occurs in the absence of exercise, is also known as non-exertional, and is the most common type of heatstroke that veterinarians treat.

• Exercise-induced heatstroke, or exertional heatstroke, occurs after strenuous play or activity.

• Malignant hyperthermia is a rare reaction to anesthesia or other drugs in which muscles experience increased contractions and break down, causing increased body temperature.

• Toxicity from substances such as hops, excessive thyroid hormone, or compounds that lead to seizures can also cause hyperthermia.

Hyperthermia occurs more often in the summer, especially in hot and humid climates, but can occur at any time in any environment. Risk factors for hyperthermia include:

• Brachycephalic, or short-nosed, breeds, such as Pugs, English Bulldogs, and Boston Terriers

• Overweight dogs

• Dogs with breathing conditions, such as laryngeal paralysis or obstructive airway disease

• Age: Young puppies and senior dogs are each at higher risk

• Hyperthyroidism

• Thick hair coats

• Young male dogs may be more likely to suffer from exercise-induced heatstroke

Dogs most commonly suffer from hyperthermia and heatstroke when they are trapped in a vehicle or other enclosed places like sheds or kennels.

Other causes include excessive exercise, especially in hot or humid environments. The heat production from muscle activity, often while hiking, hunting, or jogging with owners, raises the body temperature to potentially dangerous levels.

Dogs are unable to sweat like humans, and instead use panting to cool their body off. This makes it difficult for Pugs and other brachycephalic breeds, with their flat faces, to dissipate heat as efficiently as other breeds.

Malignant hyperthermia is a genetic condition in which a dog is susceptible to hyperthermia from anesthesia. Malignant hyperthermia can occur in any breed, but the following breeds may be at higher risk:

• St. Bernard

• Labrador Retriever

• Greyhound

• Border Collie

• English Springer Spaniel

• Irish Wolfhound

• Cocker Spaniel

• Doberman Pinscher

• Siberian Husky

• Pointer

Exposure to known toxic agents such as hops, mycotoxins, and compounds that cause seizures like strychnine and metaldehyde can all cause hyperthermia.

In all cases of hyperthermia, neurological damage can begin at 105.8 F. Temperatures above 106.7 F cause cellular death, and temperatures above 109 degrees are usually fatal.

How Veterinarians Diagnose Hyperthermia in Dogs

Veterinarians usually suspect hyperthermia from a dog’s behavior, physical condition, and history. Taking a dog’s temperature rectally confirms the diagnosis.

Once a veterinarian confirms the diagnosis, they will order multiple tests to determine the extent of damage. This can include a complete blood count, serum blood chemistry, and urinalysis for a baseline evaluation.  Veterinarians will monitor these tests before, during, and after the resolution of clinical signs.

Treatment of Hyperthermia in Dogs

Safely cooling a hyperthermic dog before getting to the hospital is key to increasing your pet’s chances of survival.

Prior to getting your dog to a veterinarian, begin cooling your dog in transit. Do not use cold water or ice, because this can cause blood vessel constriction and actually delay cooling. Instead, lukewarm or cool water and car vents and fans should be utilized. The dog can be soaked in water, especially around the groin, armpits, and neck. However, use caution to not submerge the head in water. Offer small amounts of cool drinking water and call the veterinarian on the way and ask for additional instructions.

In most cases, a dog will need to be hospitalized. Once under veterinary care, dogs in respiratory distress require oxygen supplementation and may even need intubation. Dogs in this situation are scared—they feel sick, cannot get enough oxygen, and may panic, which causes a further increase of body temperature.

These dogs may need sedatives to help them calm down, and all dogs will receive intravenous fluid therapy to hydrate and deliver medications. Other treatments vary, depending on the severity and clinical signs, including:

• Glucose supplementation

• Antibiotics

• Gastrointestinal protectants

• Blood products to treat bleeding disorders

• Cardiac drugs

• Pain management drugs

Mild cases of heatstroke caught early may resolve the same day. More serious and complicated cases of hyperthermia likely require hospitalization with close monitoring. Correction of the body temperature stops ongoing damage to cells, but only time and extensive veterinary care can correct the injury already done. Veterinarians will continuously monitor temperature, pulse, respiration, coagulation parameters, and other blood work to monitor organ function until they all return to normal.

Recovery and Management of Hyperthermia in Dogs

Unfortunately, due to the severity of hyperthermia, the prognosis is guarded. Approximately half of hyperthermic patients ultimately die or are euthanized. Treatment is expensive and intensive, with hospital stays averaging 1 to 6 days. Dogs with low blood sugar, coagulation changes, cardiac arrhythmias, and kidney injury are less likely to survive until discharge. Patients are more likely to return home if they survive the first 3 days after the incident.

At home, pet parents are urged to ensure their dog doesn’t overheat again. This may include more fans or air conditioning and never leaving dogs outside unsupervised. Pet parents should keep dogs quiet at home while they are recovering.

Prevention of Hyperthermia in Dogs

The single most important preventative factor for hyperthermia is to never leave your dog inside a car or other enclosed area. Even on cooler days, the inside of a car can increase by 40 F within an hour. On hot days, only go outside for short periods of time and only exercise in early morning or late evening when temperatures are cooler.

Ensure appropriate access to water, and especially monitor dogs who have previously suffered from heatstroke. Obese and overweight dogs are also more likely to become hyperthermic, so always discuss a proper and healthy weight for your dog with your veterinarian. These preventatives factors are especially critical for brachycephalic breeds but apply to all dogs.

Early recognition of hyperthermia is key. If you’re concerned your dog is suffering from hyperthermia, contact your veterinarian immediately and begin cooling procedures. Dog breeds at risk for malignant hyperthermia should talk to their veterinarian about genetic testing.