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
• Muscle tremors
• Wobbly, incoordinated or drunken gait or movement (ataxia)
• Unconsciousness in which the dog cannot be stimulated to be awakened

Causes

• 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

Risk Factors

• 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)
• Obesity
• 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