Heatstroke: what to do in the first ten minutes and what never to do

Dogs and cats shed heat almost entirely by panting, with minimal evaporation from the paw pads. When the air is hot and humid, panting stops working and core temperature climbs fast. The picture has no single typical sign: it has a progression, and it pays to read it before it turns dramatic.

The signs that move the picture from simple hyperthermia to heatstroke involve the nervous system and the circulation: staggering, a fixed stare, inability to stand, tremors, seizures, vomiting, bloody diarrhoea, gums that are brick red or conversely pale, and panting that becomes noisy and ineffective. An animal that suddenly stops panting while still hot is not improving: that is a serious sign.

The goal is not to bring the animal to normal temperature, it is to remove heat quickly and stop before going too low. The sequence below is designed to be carried out by one person, with whatever is available in a park or a yard.

1. 1

   Stop everything and move into shade

   Interrupt the run, the play or the journey. Move the animal to a shaded, ventilated spot or into a cool room. If you are in the car, turn the air conditioning to maximum and aim it at the animal.

2. 2

   Wet the whole body with cool running water

   Tap water, not iced, poured generously over neck, chest, belly, armpits and groin, where blood runs close to the surface. The water must be renewed constantly: water left sitting on the coat warms up and stops cooling.

3. 3

   Add moving air

   A fan, an improvised one made of card or an open window while driving multiply the effect of the water, because evaporation is what actually removes heat. Water without circulating air cools far less.

4. 4

   Measure temperature every five minutes

   If you have a digital thermometer, use it rectally. Without one, keep cooling for the duration of the journey and tell the clinic that you could not measure.

5. 5

   Stop at 39.4 degrees Celsius

   When the temperature falls to around 39.4 degrees, stop active cooling, towel off roughly and continue only with shade and air. Temperature keeps falling by inertia and the risk of hypothermia is real.

6. 6

   Call the clinic and set off

   Phone while someone else cools, or right after you have started. Give species, weight, the temperature you measured, the time signs began and what the animal was doing. On the way keep the cabin cool and the animal wet.

If the animal is alert and wants to drink, let it take small amounts of cool water at its own pace. Never force water into the mouth of an animal that is not swallowing well or is not fully conscious: it ends up in the airway.

Most mistakes come from good intentions and handed down advice. Some merely slow cooling down, others add real damage.

• Covering the animal with wet towels and leaving them on: within minutes the towel warms up and acts as insulation, trapping heat instead of releasing it.
• Putting ice directly on the skin or immersing the animal in iced water: this causes peripheral vasoconstriction and shivering, meaning less heat exchange and more muscular heat production, plus cold injury to the skin.
• Giving human or veterinary antipyretics on your own initiative: heat hyperthermia is not fever and does not respond to those drugs, which instead worsen the kidney and gastric risk in exactly the organs already affected.
• Forcing water into the mouth with a syringe or a bottle in a confused or semi conscious animal, with a real risk of aspiration pneumonia.
• Waiting at home because the animal looks better: late complications appear in the following hours, not in the first minutes.
• Putting a closed muzzle back on or using an unventilated carrier during transport: panting must stay unobstructed.
• Cooling well past the threshold to be safe, arriving at the clinic with a hypothermic animal in worse shape than it started.

Heatstroke does not strike at random. Studies of large dog populations followed by primary care practices show that most episodes happen during physical activity rather than in parked cars, and that some categories appear far more often than their numbers would suggest.

Cats develop heatstroke less often than dogs, simply because they are rarely made to run on a lead in summer. Feline cases almost always come from entrapment: a closed balcony, a conservatory, a shed, a washing machine or a carrier left in the sun during a journey. In cats, open mouth breathing is an abnormal sign in itself and should always be treated as urgent.

Heat damages the intestinal barrier, the kidney, the liver, the muscles and the clotting mechanisms. Much of that damage is invisible at the time: temperature has come down, the animal walks, drinks and looks tired but normal. Consequences typically appear within the following twenty four to seventy two hours.

• Bloody diarrhoea or black tarry stool, a sign of injury to the intestinal lining.
• Reduced or absent urine output, which indicates acute kidney injury and calls for fluids and serial testing.
• Pinpoint haemorrhages on gums and belly, nosebleeds or spontaneous bruising, consistent with a clotting disorder.
• Dark, almost brown urine, which can indicate muscle breakdown.
• Neurological signs that persist or appear late: disorientation, apparent blindness, seizures.
• Laboured breathing that does not improve, even after temperature has normalised.

This is why assessment after heatstroke is not a formality. Baseline blood work, checks of kidney function and clotting and a period of observation allow complications to be caught while they are still manageable. The monitoring your vet proposes will depend on the peak temperature reached, how long it lasted and the neurological status on arrival.

Almost every episode is predictable, because they arise from recurring situations. Changing habits for two or three months a year costs little and cuts the risk sharply.

1. Move long walks and intense activity to early morning and late evening, and on muggy days shorten the route rather than merely slowing down.
2. Touch the tarmac with the back of your hand for five seconds: if you cannot hold it, it cannot be walked on, and beyond pad burns the hot ground adds heat to the body.
3. Never leave an animal in a parked car, not even for a few minutes, not even in the shade with the windows ajar.
4. Carry water and a bowl on every summer outing, and offer it at regular intervals instead of waiting for the animal to ask.
5. Make sure there is always a cool shaded area reachable at home, and that the animal cannot get shut on balconies, in conservatories or in exposed rooms.
6. For brachycephalic, overweight, cardiac or older animals, lower the threshold: for them a warm humid day is already a risk condition.
7. Do not rely on cooling vests and mats as the only measure: they help, but they do not replace choosing the right hour and reducing the effort.

One last practical point concerns preparation. Knowing in advance where the nearest open clinic is, keeping a digital thermometer in the summer bag and having a current body weight for your animal are three details that change the quality of the response when it matters.