Heatstroke is a condition where the entire body overheats due to prolonged exposure to high temperatures. Sunstroke is caused by exposure to direct sunlight, and occurs as the result of heat concentration inside the brain.
Heatstroke and sunstroke occur when dogs cannot sufficiently cool their body. In many cases they are unable to achieve an optimal body temperature by sweating only, as dogs themselves only have a limited number of sweat glands to begin with. Both heat stroke and sunstroke show similar symptoms. As body temperature begins to rise, the dog starts to pant, and holds his mouth open while extending his tongue in order to enhance the cooling process. While panting, the respiratory rate increases greatly and breathing becomes shallow. In addition to respiratory changes, natural instincts lead dogs to seek out cool surfaces, to lick his coat and find water. Along with the above-mentioned high respiratory rate, rapid pulse, sunstroke and/or heatstroke may especially cause mucous membranes to become pale, lead to vomiting, apparent behavior changes or cramping fits. An elevated body temperature is dangerous because it causes severe circulatory distress. Blood is moved towards the peripheral parts of the body in order to be cooled. Unfortunately, this cooling strategy leads to a decreased supply of blood to the vital organs, and in severe cases results in shock and can possibly cause death. Old age, physical exercise, mental and physical excitement, obesity, and a dense coat of hair, are some other predisposing factors for the condition. Please take note there is an additional risk of heatstroke when dogs are locked inside a room or a car. In a situation where a dog is locked in a car, they are deprived of their natural cooling strategies, and there is a greater risk that body temperature will rise to critical levels.
Dogs are very sensitive to heat, as they can only expel body heat through a small number of sweat glands located in the pads and the tip of the nose. Sunstroke is caused by intensive sunlight onto the head and the neck, which causes heat to accumulate inside the skull. Transport of blood is impaired, especially to the brain, which may in severe cases result in a brain hemorrhage. In contrast, heatstroke describes overheating of the whole body and can occur, even if the dog is exposed to direct sunlight. The body is not capable of removing excessive body heat within a short period of time. Leaving a dog inside a locked car during summer heat is often the cause of heatstroke. Slightly lowered windows are not providing sufficient ventilation.
In very acute cases the dog will need immediate medical attention and intravenous fluid, as the condition may become life-threatening.
If symptoms are severe, you are looking at a clinical emergency. In that case the dog should be referred immediately to a veterinary practice or a clinic.