Heatstroke in Dogs

What is Heatstroke in Dogs?

Heatstroke is the most severe condition in a spectrum of heat-related illnesses. The first sign a dog may be developing heat-induced illness is typically heat cramps, characterized by muscle spasms. This is often related to dehydration and electrolyte depletion.

If the dog continues to be exposed to the heat, this will likely progress to heat exhaustion. Heat exhaustion is characterized by fatigue and weakness but may also include vomiting and diarrhea. In the heat exhaustion phase, the pet will likely still have a normal or slightly elevated temperature and dehydration.

The hallmark of the transition from heat exhaustion to heatstroke is central nervous system signs such as disorientation or seizures, an elevated temperature (greater than 104 degrees Fahrenheit), and often, multiple organ dysfunction. Heatstroke results from an inability of the body to cool down. This results in damage to the tissues of the body (inflammation), which leads to decreased blood flow to the organs and can ultimately cause organ damage and failure.

Every system in the body can be affected by heatstroke, but main ones include:

• Heart (elevated heart rate)

• Central nervous system (disorientation, seizures)

• Gastrointestinal tract (vomiting and diarrhea, often bloody)

• Kidneys

• Liver

• Coagulation system (increased risk of bleeding)

Furthermore, heatstroke overpowers the body’s defense mechanisms by damaging heat shock proteins, which are designed to protect the body from stress and heat.  

Heatstroke can occur very quickly and result in death in under an hour, especially if the pet does not have access to shade, water, and rest. This is an absolute emergency, and pet parents should take their dog immediately to the local emergency veterinary hospital if they suspect heatstroke.  

Symptoms of Heatstroke in Dogs

The signs of heatstroke include:

• Excessive panting

• Reddened gums/mucous membranes

• Tachycardia (fast heart rate)

• Dehydration 

• Elevated temperature (104 F and above) 

• Vomiting (with or without blood) 

• Diarrhea (with or without blood)

• Disorientation/stumbling

• Weakness/collapse

• Seizures/death 

Causes of Heatstroke in Dogs

There are two classic examples of how a dog develops heatstroke:  

• A dog left in the car, even on a relatively cool day: According to a recent study, the temperature inside a car increases by an average of 40 F per hour. This means even if it is only 70 F outside, the inside of the car can easily be greater than 110 F. For this reason, a dog should never be left alone in the car, even with the windows partially open.  

• A dog exercising on a hot, humid day: Use extreme caution when exercising your dog on summer days. Dogs can develop heatstroke even when walking for relatively short periods of time. Consider performing outdoor activities early in the morning or late at night and be sure to provide plenty of fresh water.  

Some dogs have a higher risk of developing heatstroke. Dogs with:

• Brachycephalic syndrome (meaning short-nosed dogs with flattened faces such as pugs or boxers)

• Heart disease

• Laryngeal paralysis

• Obesity

• Tracheal collapse

Older dogs are also at higher risk. However, any dog can develop heatstroke. Dogs are more susceptible to the effects of heat-related illnesses than humans because they are not able to cool themselves by sweating.

The main way dogs cool themselves is by panting causing water to evaporate from their tongue, but this is inefficient, and they can overheat quickly. Heatstroke cases are more commonly seen in Southern states, and in general in areas with higher temperatures and humidity. Heatstroke is becoming a growing danger due to climate change and extreme weather patterns.

How Veterinarians Diagnose Heatstroke in Dogs

Heatstroke is often a diagnosis based on history of heat exposure (being left in the car, exercising), clinical signs, and body temperature greater than 104 F). A complete medical history for any predisposing factors such as heart disease, laryngeal paralysis, and tracheal collapse is also helpful.

If you suspect your dog may be experiencing heatstroke, call your veterinarian or local emergency veterinary hospital immediately. They will likely instruct you on beginning to cool your dog prior to arrival at the hospital. This is extremely important. Cooling your pet prior to arrival at the hospital has been shown to increase their chances of survival from 50% to 80%. The cooling technique is crucial to preventing more damage.

When cooling your pet, never use ice, as it can increase the risk of shock (drop in blood pressure, further damage to organs) and even cause hypothermia. Try to move your pet to a cool or shaded area with a fan if possible. Wet your dog with room temperature water and drape wet towels on the back of the dog during transportation to the hospital.  

Once you arrive at the hospital, the veterinarian will start with a thorough physical examination to check your dog’s mental status and temperature. If you initiated cooling measure before arriving at the hospital, the temperature may be normal and will need to be carefully monitored to make sure it does not become too low, creating hypothermia.

A complete blood count, serum blood chemistry, and urinalysis will all likely be recommended for a baseline evaluation. There may already be elevation in liver and kidney values, but serial monitoring is recommended.

Treating Heatstroke in Dogs

Based on the diagnosis of heatstroke, your dog will need to be hospitalized and started on IV fluids to treat dehydration. Medication will be given to reduce or prevent symptoms of vomiting and diarrhea. Antibiotics will likely be a part of your pet’s treatment to prevent infection.

Depending on the severity of your pet’s condition, medications may also be used to help with swelling of the brain and seizure activity. Additional care may include oxygen therapy, plasma transfusions, and/or anti-arrhythmic medications as indicated.

While in the hospital, the veterinary staff will monitor your dog’s mental status, temperature, blood pressure, heart rate, and respiratory rate and effort, and may perform an electrocardiogram test. Repeat bloodwork is likely, to monitor any changes and help guide therapy.  

Recovery and Management of Heatstroke in Dogs

Early diagnosis and aggressive treatment of heatstroke are important for a dog’s survival and recovery. Recovering from heatstroke is directly related to how high the dog’s temperature was, for how long, and how quickly they arrived at the hospital. Major damage can occur when the body’s temperature reaches higher than 109 F. The prognosis is considered poor if multiple organ failure occurs.  

Most dogs that survive the initial 24 hours will live but will remain hospitalized on IV fluids and supportive care for 2-3 days. Once discharged, they will need lots of rest and extra TLC, but typically they can make a full recovery and go on to live normal lives. Your vet will likely want to check bloodwork 1-2 weeks after the heatstroke event to ensure all organs are working properly.  

Prevention of Heatstroke in Dogs

Prevention is key for heatstroke in dogs; keep in mind the following when the weather is hot:

• Always ensure that your pet has access to shade and water when outdoors.

• Only exercise dogs in cooler parts of the day (early in the morning, late at night). Even short walks can cause heatstroke in predisposed dogs or on extremely hot, humid days.

• Never leave dogs alone in cars, even on seemingly cool days. Even if the windows are left partially open or the car is parked in the shade, the inside of the car can be greater than 40 F hotter than outside.

• On hot days, keep your pet inside the house with air-conditioning, especially if they have a predisposed condition such as older age, brachycephalic syndrome, obesity, heart disease, tracheal collapse, or laryngeal paralysis.