Heat Stroke and Hyperthermia in Dogs

Increased Body Temperature and Heat Stroke in Dogs

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 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:

  • Panting

  • Dehydration

  • 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

  • Shock

  • 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

  • Seizures