Heat stroke is commonly seen in animals left in a vehicle. A dog can die in as little as twenty minutes in a car parked in direct sun (Gregory 2004). Several studies have been conducted on the internal heating of automobiles under different conditions. In 85 ° F ambient temperature, the temperature inside a car, even with the windows left slightly open, can reach 102 ° F in ten minutes and 120 ° F in thirty minutes (API 2005). A study using a dark blue sedan with medium gray interior was conducted under ambient temperatures ranging between 72 ° F and 96 ° F. The study found that the average temperature rose 3.2 ° F per five-minute interval: 3.4 ° F with the windows closed; 3.1 ° F with the windows open 1.5 inches. The interior temperature reached its maximum in sixty minutes with 80% of the rise within the first thirty minutes regardless of the outside temperature. Even at the lowest ambient temperature the internal vehicle temperature reached 117 ° F with an average maximum increase of approximately 41 ° F (McLaren, Null, and Quinn 2005).
Another study was conducted using a dark colored sedan and light colored minivan. The conditions were 93 ° F ambient temperature, partly cloudy, and 53% relative humidity. The study found that within twenty minutes both cars exceeded 125 ° F and reached approximately 140 ° F in forty minutes (Gibbs, Lawrence, and Kohn 1995). The exterior color of the vehicle does not seem to make a difference to the internal temperature in the passenger compartment, but darker-colored cars have a higher temperature in the trunk (Di Maio and Di Maio 2001). The heating of dark colored interior components can reach 180 ° F to more than 200 ° F, which heats the adjacent air by conduction and convection (McLaren, Null, and Quinn 2005). Shade vs. direct sun can make a difference on the inside temperature. None of the studies found that lowering the windows had any significant effect on the inside temperature unless they were fully open.
Dogs with heat stress start to pant. Then they begin to salivate and their tongue hangs out of their mouth. When the rectal temperature reaches 105 ° F, there is loss of equilibrium, and uncontrolled hyperpyrexia (abnormally high fever) may occur. The dog becomes excited and starts to bark. At 109 ° F the dog becomes ataxic (loss of coordination) with possible abdominal swelling from aerophagia (excess air swallowing which goes to the stomach), and collapses (Gregory 2004). Cats have a limited ability to sweat and primarily sweat in their pads. The cat will first pant through its nose. When the rectal temperature reaches 103 ° F, the cat starts open-mouthed panting. The cat may groom to spread saliva for evaporation cooling (Gregory 2004).
The range of clinical signs that occurs in dogs with heat stroke includes: rapid breathing, excessive panting, severe respiratory distress, dehydration, vomiting which may become bloody, diarrhea which may become bloody, collapse, mental depression, coma, and/ or seizures. Seizures occur less frequently than mental depression and coma.
A dog that is exposed to extremely high temperatures in a locked car on a sunny day will die more quickly than one that dies from other causes of heat stroke. Because these dogs die more quickly, the range of clinical signs may be more limited than in dogs that are not exposed to this environmental extreme.
(2012-09-27). Veterinary Forensics: Animal Cruelty Investigations. Wiley. Kindle Edition.