Hyperthermia is an elevation in body temperature that is above the generally accepted normal range. Although normal values for dogs vary slightly, it usually is accepted that body temperatures above 103° F (39° C) are abnormal.
Heat stroke, meanwhile, is a form of non-fever hyperthermia that occurs when heat-dissipating mechanisms of the body cannot accommodate excessive external heat. Typically associated with temperature of 106° F (41° C) or higher without signs of inflammation, a heat stroke can lead to multiple organ dysfunction.
This condition can lead to multiple organ dysfunction. Temperatures are suggestive of non-fever hyperthermia. Another type, malignant hyperthermia, is an uncommon familial non-fever hyperthermia that can occur secondary to some anesthetic agents.
Hyperthermia can be categorized as either fever or non-fever hyperthermias. Fever hyperthermia results from inflammation in the body (such as the type that occurs secondary to a bacterial infection). Non-fever hyperthermia results from all other causes of increased body temperature.
Other causes of non-fever hyperthermia include excessive exercise, excessive levels of thyroid hormones in the body, and lesions in the hypothalamus, the part of the brain that regulates body temperature.
Non-fever hyperthermia occurs most commonly in dogs (as opposed to cats). It can affect any breed, but is more frequent in long-haired dogs and short-nosed, flat-faced dogs, also known as brachycephalic breeds. It can occur at any age but tends to affect young dogs more than old dogs.
Symptoms and Types
Hyperthermia can be categorized as either fever or non-fever hyperthermias; heat stroke is a common form of the latter. Symptoms of both types include:
- Excessive drooling (ptyalism)
- Increased body temperature - above 103° F (39° C)
- Reddened gums and moist tissues of the body
- Production of only small amounts of urine or no urine
- Sudden (acute) kidney failure
- Rapid heart rate
- Irregular heart beats
- Stoppage of the heart and breathing (cardiopulmonary arrest)
- Fluid build-up in the lungs; sudden breathing distress (tachypnea)
- Blood-clotting disorder(s)
- Vomiting blood (hematemesis)
- Passage of blood in the bowel movement or stool
- Black, tarry stools
- Small, pinpoint areas of bleeding
- Generalized (systemic) inflammatory response syndrome
- Disease characterized by the breakdown of red-muscle tissue
- Death of liver cells
- Changes in mental status
- Muscle tremors
- Wobbly, uncoordinated or drunken gait or movement (ataxia)
- Unconsciousness in which the dog cannot be stimulated to be awakened
- Excessive environmental heat and humidity (may be due to weather conditions, such as a hot day, or to being enclosed in an unventilated room, car, or grooming dryer cage)
- Upper airway disease that inhibits breathing; the upper airway (also known as the upper respiratory tract) includes the nose, nasal passages, throat (pharynx), and windpipe (trachea)
- Underlying disease that increases likelihood of developing hyperthermia, such as paralysis of the voice box or larynx; heart and/or blood vessel disease; nervous system and/or muscular disease; previous history of heat-related disease
- Poisoning; some poisonous compounds, such as strychnine and slug and snail bait, can lead to seizures, which can cause an abnormal increase in body temperature
- Anesthesia complications
- Excessive exercise
- Previous history of heat-related disease
- Age extremes (very young, very old)
- Heat intolerance due to poor acclimatization to the environment (such as a heavy coated dog in a hot geographical location)
- Poor heart/lung conditioning
- Underlying heart/lung disease
- Increased levels of thyroid hormone (hyperthyroidism)
- Short-nosed, flat-faced (brachycephalic) breeds
- Thick hair coat
- Dehydration, insufficient water intake, restricted access to water
Early recognition of the symptoms of heat stroke is key to a prompt recovery. If your dog's increased body temperature can be linked to environmental temperature, such as weather, an enclosed room, grooming cage or exercise, the first immediate step will be to attempt to lower the body temperature.
Some external cooling techniques include spraying the dog down with cool water, or immersing the dog's entire body in cool – not cold – water; wrapping the dog in cool, wet towels; convection cooling with fans; and/or evaporative cooling (such as isopropyl alcohol on foot pads, groin, and under the forelegs). Stop cooling procedures when temperature reaches 103° F (using a rectal thermometer) to avoid dropping below normal body temperature.
It is very important to avoid ice or very cold water, as this may cause blood vessels near the surface of the body to constrict and may decrease heat dissipation. A shivering response also is undesirable, as it creates internal heat. Lowering the temperature too quickly can lead to other health problems, a gradual lowering is best. The same guideline applies to drinking water. Allow your dog to drink cool, not cold, water freely. However, do not force your dog to drink.
You will need to have your dog examined by a veterinarian to ensure that a normal temperature has been reach and has stabilized, and that no long lasting damage has taken place within the organs or brain. Complications, such as a blood-clotting disorder, kidney failure, or fluid build-up in the brain will need to be immediately and thoroughly treated. Your doctor will check your dog's blood clotting times, and kidney function will be analyzed in part by urinalysis. An electrocardiogram may also be used to observe your dog's heart capabilities and any irregularities that might have resulted as a result of the hyperthermic condition.
In many cases patients need to be hospitalized until their temperature is stabilized, and may even need intensive care for several days if organ failure has occurred. Oxygen supplementation via mask, cage, or nasal catheter may be used for severe breathing problems, or a surgical opening into the windpipe or trachea may be required if upper airway obstruction is an underlying cause or a contributing factor. Intravenous feeding or a special diet may need to be prescribed until your dog's organs have recovered to handle a normal diet again.
Underlying disease conditions or factors that increase the likelihood of developing hyperthermia will also need to be corrected and treated if possible (e.g., obesity, heart/lung disease, grooming with respect to environmental temperatures, restricting activity with respect to age).
Dogs that have suffered an episode of hyperthermia are prone to experiencing it again. Be aware of the clinical signs of heat stroke so you may respond quickly to an episode. Know how to cool your dog properly, and talk to your veterinarian about the appropriate procedures for maintaining proper body temperature and lowering it in the safest way possible.
If your dog is older, or is a brachycephalic breed that is prone to overheating, avoid taking your dog out during the hottest times of day, or leaving the dog in places that can become too hot for your dog, like a garage, sunny room, sunny yard, or car. Never leave your dog in a parked car, even for only a few minutes, as a closed car becomes dangerously hot very rapidly. Always have water accessible to your dog; on hot days you might even add ice blocks for your dog to lick.
If you have not done so already, you may wish to invest in a pet CPR class. It can mean the difference between your dog living or dying should an episode of heat stroke occur.