Overheating (Hyperthermia)
Hyperthermia refers to a condition where an animal’s body temperature rises above the normal physiological range. In dogs and cats, the normal body temperature is between 38.0 and 39.0 °C. In veterinary medicine, hyperthermia is defined as a rectal temperature above 39.5 °C. Unlike fever, where the body actively raises its set temperature (e.g., in response to infections), hyperthermia is a passive overheating where the body’s own cooling mechanisms are overwhelmed.
Dogs and cats have limited means of thermoregulation. Unlike humans, they have few sweat glands distributed across their bodies. Dogs primarily regulate their body temperature through panting, releasing heat through the moist mucous membranes of the respiratory tract. Cats use panting as well as grooming their fur for cooling through evaporation. In both species, extreme heat exposure or physical exertion can quickly overwhelm these cooling mechanisms, leading to a dangerous rise in body temperature.
Causes
The causes of hyperthermia in dogs and cats are diverse. The most common form is the classic heat stroke, triggered by high ambient temperatures. Enclosed spaces like cars are particularly dangerous, as they can heat up to over 60°C within minutes in the sun. Prolonged exposure to direct sunlight without shade can also lead to overheating.
Another common cause is hyperthermia resulting from intense physical activity in warm weather. This mainly affects dogs that play, run, or train too intensively in the heat. Stress and anxiety can also contribute to a rise in temperature as they increase the metabolic rate.
Certain groups of animals are particularly at risk. These include brachycephalic (short-headed) breeds such as pugs, bulldogs, boxers, or Persian cats, whose shortened airways make it difficult to dissipate heat through panting. Overweight animals, puppies and seniors, as well as animals with pre-existing conditions (especially heart and respiratory diseases) are also at increased risk. Long-haired breeds and animals with dark fur absorb more solar heat and overheat faster.
Symptoms
- Intense panting
- Weakness
- Dizziness
- Staggering
- Lying on the side
- Weak, rapid pulse
- Seizures
- Vomiting
The symptoms of hyperthermia develop progressively and can vary depending on severity. In early stages, affected animals show increased panting, elevated respiratory rate, increased heart rate, and restless behavior. The mucous membranes appear intensely red and salivation increases. Many animals actively seek cooler spots or lie down on cool surfaces.
As overheating progresses, weakness, dizziness, and coordination problems occur. The animals may stagger or show an unsteady gait. Vomiting and diarrhea are common accompanying symptoms. The respiratory rate continues to increase while the depth of breathing decreases – panting becomes more shallow and ineffective.
In severe cases, neurological symptoms such as muscle tremors, seizures, or even unconsciousness occur. The pulse becomes weak and rapid, and the mucous membranes may turn bluish due to oxygen deficiency. Without immediate treatment, organ failure, coagulation disorders (DIC), cerebral edema, and ultimately death are imminent. At body temperatures above 43°C, the prognosis is extremely unfavorable, as irreversible cell damage occurs in vital organs.
First Aid
- Move your pet to a shaded, cool place.
- Remove the collar.
- Wet the animal’s belly (less hair) with water or place wet towels on the animal.
- If you’re at home and have enough water available, soak your entire pet to the skin.
- Offer water that’s not too cold, but don’t force it to drink.
If your pet is unconscious or breathing doesn’t calm down or body temperature is around 40 degrees Celsius or rising to this range, take your pet to a veterinarian immediately.
There is a risk of “heat stroke”, which can lead to brain and other organ damage and is life-threatening.
If possible, continue cooling your pet with wet towels until you reach the veterinarian.
Diagnosis
The diagnosis of hyperthermia is primarily made by measuring body temperature in conjunction with clinical examination and medical history. Rectal temperature measurement is the gold standard. It is important to distinguish between hyperthermia and fever, as the treatment approaches differ. For hyperthermia, cooling is the primary focus, while for fever, treating the underlying cause is the priority.
In veterinary practice, additional diagnostic procedures are used to assess the extent of organ damage. Blood tests provide information about electrolyte imbalances, kidney and liver function, and acid-base balance. A complete blood count can indicate inflammation or coagulation disorders. Blood lactate measurement serves as a marker for tissue perfusion and the severity of shock.
In severe cases, imaging techniques such as ultrasound may be used to identify organ damage. An ECG helps to detect heat-related cardiac arrhythmias. In specialized facilities, advanced neurological examinations can also be conducted to assess brain damage.
Further veterinary measures
In the small animal practice / clinic, your pet can be shaved and further cooling promoted.
Consequential damages such as cerebral edema, disruption of water, electrolyte, and acid-base balance, or hypoglycemia can be detected and treated through laboratory diagnostic tests.
Supplement
Treating hyperthermia requires quick action and follows a multi-step approach. Initial care aims at controlled lowering of body temperature. This should be done gradually to avoid too rapid a temperature drop, which can be dangerous in itself.
As an immediate measure, the animal is moved to a cool, shaded place and wetted with lukewarm (not ice-cold) water, especially on thinly haired areas like the belly, armpits, and groin, where large blood vessels run close to the skin surface. Damp towels can be applied and changed regularly. Fans support evaporative cooling. The temperature should be continuously monitored, and cooling should be stopped when about 39.5°C is reached to avoid hypothermia.
Intensified therapy is provided in the veterinary practice or hospital. Intravenous fluid administration corrects dehydration and supports circulatory function. Oxygen is administered as needed. Medication may include anticonvulsants for convulsions, mannitol for cerebral edema, and coagulation factors for blood coagulation disorders. In severe cases, intensive care monitoring with continuous ECG and blood pressure monitoring may be necessary.
Prognosis and aftercare
The prognosis for hyperthermia depends significantly on the peak body temperature reached, the duration of overheating, and the speed of initiated treatment. With early intervention and moderate overheating, the prognosis is usually good. In severe cases with temperatures above 42 °C and existing organ damage, the prognosis may be poor despite intensive treatment.
Aftercare plays a crucial role in complete recovery. In the first 24-48 hours following heatstroke, there is an increased risk of complications such as acute kidney failure, liver damage, or coagulation disorders. Regular follow-up checks with blood tests are therefore important to detect and treat organ damage early.
In the long term, animals that have survived severe heatstroke may develop increased sensitivity to heat. Owners should therefore be particularly cautious and consistently implement preventive measures. Some animals may also retain neurological residual effects that require longer-term therapy.
Summary
Hyperthermia in dogs and cats represents a potentially life-threatening emergency that requires quick action. The main causes are high ambient temperatures and excessive physical exertion in warm conditions. Brachycephalic breeds, overweight animals, very young or old animals, and those with pre-existing conditions are particularly at risk.
Symptoms develop progressively, from increased panting to coordination problems, unconsciousness, and organ failure. Diagnosis is made through temperature measurement and clinical examination, supplemented by laboratory diagnostic procedures to assess organ damage.
Treatment includes controlled lowering of body temperature, fluid therapy, and management of complications. The prognosis is usually good with early intervention but can be poor in severe cases with organ failure. Preventive measures such as avoiding exertion in heat and never leaving animals in cars are crucial to prevent hyperthermia.
Outlook on current research
Current research in the field of hyperthermia in small animals focuses on several key areas. New biomarkers are being investigated to enable earlier detection of organ damage. Studies on specific laboratory parameters such as heat shock proteins could allow for more precise prognosis in the future.
Another area of research concerns innovative cooling methods. Experimental approaches such as selective brain cooling or special cooling infusions are showing promising results in initial studies. The development of drugs specifically targeting the inflammation cascade triggered by heat is also a focus of current investigations.
Genetic studies in brachycephalic breeds could lead to long-term breeding recommendations that reduce the risk of heat-related problems. In parallel, improved prevention strategies are being developed, including wearables for temperature monitoring and early warning systems for pet owners.
Frequently asked questions (FAQs)
- At what temperature is hyperthermia considered dangerous for dogs and cats?
Acute danger exists at a body temperature of about 41°C. Temperatures above 42°C can already lead to irreversible organ damage. - How long does it take for an animal to overheat in a closed car?
At outside temperatures from 20°C, a car in the sun can heat up to dangerous temperatures within 10-30 minutes, even with slightly open windows. - Which dog breeds are particularly susceptible to overheating?
Particularly at risk are brachycephalic (short-headed) breeds such as pugs, bulldogs, boxers, Pekingese, as well as long-haired breeds and dogs with dark fur. - Can I give my overheated animal ice cubes or very cold water?
No, water that is too cold can cause shock and constrict blood vessels, which worsens heat dissipation. Instead, use lukewarm to cool water. - How do I know if my animal has heat stroke or is just exhausted?
Extreme exhaustion can be an early sign of heat stroke. Look out for heavy panting, staggering gait, glassy eyes, dark red tongue, and dullness as warning signs. - Can an animal suffer long-term damage after surviving heat stroke?
Yes, possible long-term consequences include kidney and liver damage, neurological problems, and increased sensitivity to heat in the future. - How can I best cool my animal on hot days?
Provide cool, shady resting places, set up several water bowls, use damp towels as a lying surface, and plan walks in the early morning or late evening hours. - Is it dangerous if my dog shivers after swimming in cold water?
Slight shivering after swimming is normal and a sign that the body is trying to produce heat. However, be careful not to let hypothermia set in. - Can cats also suffer from heat stroke?
Yes, although cats can often handle heat better than dogs, they are also at risk, especially if they are trapped in overheated rooms or if they are brachycephalic breeds such as Persian cats. - How do I prepare my animal for hot summer days?
Gradually acclimate your animal to rising temperatures, ensure adequate fluid intake, avoid obesity, and adjust activities to the temperatures.
Literature
- Bruchim Y, Klement E, Saragusty J, Finkeilstein E, Kass P, Aroch I.: Heat stroke in dogs: A retrospective study of 54 cases (1999-2004) and analysis of risk factors for death. J Vet Intern Med. 2006 Jan-Feb;20(1):38-46.
- Jenny McIntosh: Heat stroke – a seasonal challenge. In: kleintier konkret. Volume 20, Issue 2, 2017, pp. 23-31.
- Löwe, G. and Löwe, O. (2021). Emergencies in Dogs and Cats – A Veterinary Guide. Kynos-Verlag. 208 p.
- Bruchim Y, Segev G, Kelmer E, et al. Hospitalized dogs recovery from naturally occurring heatstroke; does serum heat shock protein 72 can provide prognostic biomarker? Cell Stress Chaperones. 2020;25(3):455-464.
- Hall EJ, Carter AJ, O “Neill DG. Dogs Don” t Die Just in Hot Cars—Exertional Heat-Related Illness (Heatstroke) Is a Greater Threat to UK Dogs. Animals. 2020;10(8):1324.
- Hemmelgarn C, Gannon K. Heatstroke: Clinical Signs, Diagnosis, Treatment, and Prognosis. Compendium on Continuing Education for the Practicing Veterinarian. 2021;35(7):E3.
- Johnson SI, McMichael M, White G. Heatstroke in small animal medicine: a clinical practice review. Journal of Veterinary Emergency and Critical Care. 2019;29(1):9-22.
- Teichmann S, Türk J, Dörfelt R. Hyperthermia, heat stroke and malignant hyperthermia in dogs and cats. Tierärztliche Praxis Kleintiere. 2022;42(1):13-20.
Risk of overheating when the dog is left in the car during the warm season.