Hyperthermia

Heatstroke is the most severe of the heat-induced illnesses (Drobatz, 2015). It is classified as external (overheating from exercise) or non-external (classic heatstroke). Any body system may be involved; however, the major systems involved are the cardiovascular, central nervous, gastrointestinal, renal, and coagulation systems. There are three types of heat illness, presenting as a continuum from least to the most severe (Drobatz, 2015).

■ Heat cramping: Muscle spasms from sodium and chloride loss

■ Heat exhaustion/prostration: Fatigue, weakness, muscle tremors, vomiting, and diarrhea

■ Heatstroke: Severe central nervous system disturbances and multi-organ dysfunction

A more recent definition of heatstroke is hyperthermia associated with a systemic inflammatory response leading to a syndrome of multi-organ failure in which encephalopathy predominates.

Heatstroke is the increase of core body temperature causing heat-induced illness (Drobatz, 2015). Heatstroke within domestic animals is more common in dogs and cats (Drobatz, 2015). A dog’s body dissipates heat via multiple methods. One is the conduction of heat through cutaneous vasodilation ridding the body of heat by direct contact with a cooler surface. Convection occurs via postural changes and cutaneous vasodilation allowing air blowing over a body surface to remove the warmed air layer next to the animal’s body. Radiation is the direct removal of radiation (infrared heat) into the environment, through cutaneous vasodilation. The final method and the most important when the environmental temperatures equal core body temperatures is evaporation. The first three methods discussed enact when environmental temperatures are at or below 89.6°F (32°C). (Merck & Miller, 2013). Dogs cannot sweat like humans and will dissipate heat by evaporation by panting. The oral cavity and nasal passages supply a large surface area for loss of water (evaporation) from the moist mucous membranes (Merck & Miller, 2013). Conditions that combine heat load and decreased heat dissipation can result in rapid and extreme body temperature elevation. Heatstroke occurs when the heat-disseminating mechanisms can no longer compensate for the rising body temperature, such as occurs with entrapment (in a hot vehicle) or exposure to extreme environmental temperatures without shelter or water (tying out) (Merck & Miller, 2013).

In animal abuse cases, hyperthermia is observed when animals are left inside a hot car or building or tethered outside without access to water or any protection from elevated environmental temperaturesand direct sunlight (Merck & Miller, 2013). In addition, the environmental temperature is affected by the relative humidity. As the humidity increases, the heat index is higher than the recorded temperature (Merck & Miller, 2013).

Animals left in a hot vehicle commonly develop heatstroke. A dog may die in as little as 20 minutes in a parked car in direct sunlight even with the windows cracked slightly (Merck & Miller, 2013). There have been multiple studies conducted on the internal heating of vehicles in different conditions. In one study the average temperature rose 3.2°F (1.8°C) every 5 minutes with the windows closed and 3.1°F (1.7°C) with the window open several inches, the inside temperature eventually rising to its maximum level within 1 hour, with over 80% of the rise within the first 30 minutes regardless of the outside temperature. Even at low ambient temperatures, the internal temperature of a vehicle reached 117°F (47°C) with an average maximum increase of 41°F (5°C) (Merck & Miller, 2013). Even at 85°F (29°C) ambient temperature, the internal temperature even with the windows left open 1-2 inches can reach 102°F (39°C) within 10 minutes and 120°F (49°C) in 30 minutes (Merck & Miller, 2013). The temperature inside a car can rise 20°F in just 10 minutes. Even on a 70°F day it can become 110°F in a vehicle (AVMA, 2018), and cracking the windows makes no difference.

A dog’s body maintains body temperature within a narrow range called the set point. When body temperature deviates from the set point, physiologic processes are initiated to elevate or decrease the body temperature. When a dog’s body temperature reaches 106°F (41° C) the dog is in danger of a heat-caused illness. If the body temperature reaches above 110°F (43°C) there is a breakdown of the cellular processes and the dog can die in 5-15 minutes.

Heatstroke is not commonly reported in cats. This may be to the lack of detection (Merck & Miller, 2013). When it is discovered, it is usually caused by the cat being subjected to a sudden increase in temperature or confinement in high temperatures without an escape (Merck & Miller, 2013).

It is important to stress most state laws for animal abuse regarding animals in a hot car have verbiage concerning possible physical harm or actual physical harm. This stresses the importance of veterinary testimony to articulate what can happen even if fortunately, it did not.