Bradbury, J., Hall, E., Carter, A. and O'Neill, D.G., 2023. Canine heat-related illness–new perspectives from recent research. Companion Animal, 28(7), pp.2-5

A summary

Heat related illness, also referred to as heatstroke, is a condition where an animal's body temperature is so high, that they cannot thermoregulate i.e. reduce it using normal bodily function. There are 2 types – environmental and exertional. Environmental is related directly to context, being in a hot car or exposed to heat. Exertional is related to exercise or being active usually in hot conditions, exertion related heatstroke accounted for almost 75% of all heat related illness presented to a vet in 2016. The average wet bulb globe temperature reading for heat related illness was 16 degrees celsius.

Risk Factors

Breed, age, bodyweight and underlying health issues. 

9 breeds were shown as having increased risk of heat related illness: Chow Chow, English Bulldog, French Bulldog, Dogue de Bordeaux, Greyhound, Pug, English Springer Spaniel, Cavalier King Charles Spaniel and Golden Retriever (Figure 1) (Hall et al, 2020b)

Dogs under the age of 2 were more at risk -- suggesting they undertake more intense exercise perhaps. Dogs over 12 were also more at risk most likely due to age related limitations around thermoregulation.

Brachycephalic breeds were more at risk than mesocephalic breeds, most likely due to the restrictions brachycephaly imposes on panting, an essential part of a dogs thermoregulatory system.

Overweight dogs were more at risk, with dogs weighing under 10kg showing reduced risk.

Clinical signs and grading

"Dogs, like humans, experience grades of heat-related illness, progressing from mild (characterised by lethargy and altered respiration) to moderate (gastrointestinal disorder, episodic collapse, single seizure) and then severe disease (neurological derangement, bleeding disorders, gastrointestinal haemorrhage and damage of the liver, kidneys or both). Dogs presenting with severe heat-related illness had 65 times the risk of death compared to dogs with mild heat-related illness (Hall et al, 2022). Therefore, dog owners should be educated to recognise signs of mild heat-related illness, and how to prevent disease progression." (Bradbury et al. 2023)

Mythbusting the treatment

In the past gradual cooling has been advised, this is no longer the case. This was advised due to the idea that shivering due to excessive cooling could begin to heat the body further. This has been debunked. 

Cold water immersion and evaporative cooling are more effective. Immersion is best for healthy, young dogs, with evaporative being better for geriatric, comatose or dogs with comorbidities. 

Active cooling should take place prior to transport to vet practice.