Low Body Temperature (Hypothermia)
Hypothermia, colloquially also referred to as undercooling, is a pathophysiological condition in which the core body temperature drops below the normal range. In dogs, the normal body temperature is between 37.5°C and 39.0°C, in cats between 38.0°C and 39.5°C. Hypothermia is defined when the body temperature falls below 37.5°C in dogs and below 38.0°C in cats. The severity of hypothermia is classified into three grades: mild hypothermia (35-37°C), moderate hypothermia (32-35°C), and severe hypothermia (below 32°C). At temperatures below 28°C, there is acute danger to life.
Temperature regulation in mammals occurs via the thermoregulatory center in the hypothalamus. This controls various physiological mechanisms for heat production and retention. Dogs and cats can regulate their body temperature through muscle shivering, vasoconstriction of peripheral blood vessels, and metabolic adaptations. However, compared to humans, they have a higher risk of hypothermia due to their smaller body mass and, in some breeds, a less favorable ratio of body surface area to body volume.
Causes
Low body temperature is defined as when the body temperature drops below 36 degrees Celsius.
The cause can be a cold ambient temperature, so that the body is no longer able to maintain its normal body temperature through its own heat generation. This can occur especially during a stay in cold water (Fig.), in anesthetized animals, or in case of severe fluid deficiency.
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The causes of hypothermia in dogs and cats are diverse and can be divided into environmental, medical, and iatrogenic factors:
Environmental factors include prolonged exposure to low temperatures, primarily in combination with wetness or wind. Particularly dangerous is staying in cold water, as water conducts body heat about 25 times faster than air. Falling through ice can also lead to life-threatening hypothermia within a very short time.
Medical causes include severe general illnesses such as shock conditions, sepsis, severe metabolic disorders (e.g., hypoglycemia, hypothyroidism), poisonings, or brain damage that impair the thermoregulation center. Dehydration can also lead to a reduced ability to regulate temperature.
Iatrogenic hypothermia often occurs during surgical procedures. The effect of anesthetics impairs thermoregulation, and open body cavities, cold infusion solutions, and the use of disinfectants lead to increased heat loss.
Particularly at risk are very young or old animals, animals with low body weight, short-haired breeds, and animals with pre-existing conditions, especially those affecting metabolism or the cardiovascular system.
Symptoms
Symptoms of hypothermia develop slowly, except in cases of immersion in icy water. These may include:
- Shivering
- Reduced, shallow breathing
- Decrease in heart rate
- Dizziness
- Unconsciousness
The clinical signs of hypothermia develop progressively as body temperature drops and vary depending on severity. In mild hypothermia (35–37°C), animals initially show muscle shivering as a compensatory mechanism for heat production. The animals appear restless, seek warm places, and huddle to reduce body surface area. Peripheral body parts such as ears, paws, and tail feel cool.
In moderate hypothermia (32–35°C), shivering subsides as energy reserves are depleted. The animals become increasingly lethargic and show neurological symptoms such as coordination disorders and decreased reflexes. Heart rate decreases, pulse weakens, and breathing slows. Mucous membranes appear pale or bluish due to peripheral vasoconstriction and reduced tissue oxygen supply.
Severe hypothermia (below 32°C) leads to pronounced clouding of consciousness up to coma. Muscles become stiff, pupils barely react to light. Heart rate drops drastically, cardiac arrhythmias occur, and ventricular fibrillation may develop. Breathing becomes shallow and irregular. At this stage, there is acute danger to life, and death occurs without immediate treatment.
Particularly problematic is that hypothermic animals can be in an apparently lifeless state, although signs of life are still present. Therefore, the principle applies: “A hypothermic animal is only dead when it is warm and dead.”
First Aid
- Bring your pet to a warm room.
- If that’s not possible, protect it from wind and further cooling by wrapping it in a blanket or similar.
- Dry the fur.
- Use a heating blanket for warming.
- When using a hot water bottle or heating pad, make sure it’s not too hot.
- Don’t warm up your pet too quickly, e.g., with a radiant heater or a hot bath.
- Don’t massage your pet.
- Offer warm water or broth to drink. But don’t force any liquids.
If your pet needs a longer operation under general anesthesia, its body temperature may drop.
Leave your pet with the veterinarian for monitoring after surgery until it is fully conscious. By then, the body temperature will have normalized.
In case of low body temperature due to fluid deficiency (dehydration), there is an underlying condition such as vomiting or diarrhea that requires treatment.
Take your pet to a veterinarian.
Diagnosis
The diagnosis of hypothermia is primarily based on measuring body temperature using a rectal thermometer. It should be noted that standard thermometers often only measure down to 34°C or 32°C; special thermometers are needed for lower temperatures. During the clinical examination, vital parameters such as heart rate, respiratory rate, capillary refill time, and mucous membrane color are also assessed.
Further examinations are useful for assessing the severity and possible complications. A blood count can provide indications of infections or inflammations that may have contributed to hypothermia. Blood gas analyses show disturbances in acid-base balance and oxygen supply. Electrolyte determinations are important as hypothermia can lead to electrolyte shifts. An ECG is used to detect cardiac arrhythmias, which are common in severe hypothermia.
In unconscious animals with unclear causes of hypothermia, imaging techniques such as X-ray, ultrasound, or CT may be necessary to rule out underlying diseases. The diagnosis should always include distinguishing between primary (environmental) and secondary (disease-related) hypothermia, as this has implications for therapy and prognosis.
Further veterinary measures
Establishing venous access and securing the airway are the first measures.
Rewarming must be done gradually, as otherwise there is a risk of ventricular fibrillation. Adequate fluid therapy with pre-warmed infusion solutions counteracts this.
The further procedure differs depending on the degree of hypothermia and the other initial conditions.
In cases of severe hypothermia (<27 ºC), ventricular fibrillation or cardiac arrest may occur, necessitating chest compressions.
Defibrillation should only be performed once a body temperature of at least 30 ºC has been reached.
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The treatment of hypothermia depends on its severity and accompanying circumstances. The basic principle is controlled, slow rewarming to avoid dangerous complications such as the afterdrop phenomenon (further decrease in core temperature due to cold blood returning from the periphery) or reperfusion injuries.
For mild hypothermia (35–37 °C), passive warming measures are often sufficient: The animal is brought into a warm room, wrapped in pre-warmed blankets, and protected from drafts. Wet fur should be carefully dried. Warm, sweetened liquids can be offered if the animal is conscious and able to swallow.
Moderate hypothermia (32–35 °C) requires additional active external heat supply through heating pads, hot water bottles, or heating blankets, which should be wrapped in towels to avoid direct contact. Warming should begin on the torso, not the extremities, to minimize the return of cold blood to the heart. Intravenous fluid therapy with infusion solutions warmed to body temperature supports circulatory stabilization.
In severe hypothermia (below 32 °C), intensive medical care is essential. In addition to the mentioned measures, active core warming techniques are used, such as flushing body cavities with warm fluids or extracorporeal warming procedures. Rewarming should occur at a rate of 0.5-2 °C per hour. Continuous monitoring of vital functions is necessary, as cardiac arrhythmias, electrolyte shifts, and circulatory instability can occur during the warming phase.
Accompanying measures may include oxygen administration, glucose infusions for hypoglycemia, and in severe cases, medications for circulatory stabilization. In case of cardiac arrest, cardiopulmonary resuscitation is performed, noting that defibrillation is only effective in severely hypothermic animals once a body temperature of over 30 °C is reached.
Prognosis and aftercare
The prognosis for hypothermia depends significantly on the severity, duration of hypothermia, and any accompanying illnesses. For mild to moderate hypothermia without complications, the prognosis is good to very good with timely treatment. Animals usually recover completely without long-term effects.
In severe hypothermia (below 32°C), the prognosis worsens significantly. Complications such as cardiac arrhythmias, coagulation disorders, kidney failure, or brain damage can occur. Nevertheless, successful resuscitations have been documented even at very low body temperatures, especially in young, previously healthy animals.
Aftercare includes careful monitoring of vital functions and body temperature for 24-48 hours, as relapses can occur. Regular checks of kidney function, electrolyte balance, and blood count are recommended to detect subsequent damage early. Neurological examinations should be conducted on animals that have survived severe hypothermia to assess possible brain damage.
Preventive measures to avoid repeated hypothermia must be discussed with the owners. These include appropriate weather protection, adjustment of activities in cold weather, and special precautions for at-risk patients such as old or sick animals.
Summary
Hypothermia in dogs and cats is a potentially life-threatening condition characterized by a drop in body temperature below the physiological normal range. It can be caused by environmental factors, underlying diseases, or iatrogenic factors. Particularly at risk are very young or old animals, small breeds, and animals with pre-existing conditions.
Clinical symptoms develop progressively as body temperature drops, ranging from muscle tremors and restlessness in mild hypothermia to unconsciousness, severe cardiac arrhythmias, and respiratory arrest in severe hypothermia. Diagnosis is primarily made by measuring body temperature and clinical examination, supplemented by further diagnostics to assess complications and underlying diseases.
Therapy is based on the principle of controlled, slow rewarming, adapted to the severity of hypothermia. In severe hypothermia, intensive care with continuous monitoring of vital functions is essential. The prognosis is good for mild to moderate hypothermia but worsens with increasing severity and duration of hypothermia.
Through preventive measures such as appropriate weather protection, adjustment of activities in cold weather, and special caution with at-risk patients, the occurrence of hypothermia can be prevented in many cases.
Outlook on current research
Research in the field of hypothermia in small animals is currently focusing on several promising areas. New insights into therapeutic hypothermia show that controlled, mild cooling after certain emergency situations such as cardiac arrest or traumatic brain injury can have neuroprotective effects. This technique, already established in humans, is now being adapted for veterinary use.
Innovative warming systems for the perioperative phase are being developed to minimize the frequently occurring iatrogenic hypothermia during surgical procedures. These include improved heating mats with precise temperature control, warm air blowers, and special insulation materials that more effectively retain body heat.
In the field of intensive care, new protocols for treating severe hypothermia are being researched, including optimized rewarming strategies and pharmacological approaches to minimize reperfusion injury. The development of portable devices for extracorporeal warming could find application in veterinary medicine in the future.
Molecular biological studies are examining the cellular mechanisms of cold adaptation and cold damage, which could lead to new therapeutic approaches. Biomarkers for early detection of organ damage after hypothermia are being evaluated to improve prognosis assessment and enable targeted therapies.
Frequently asked questions (FAQs)
- At what temperature is hypothermia considered to occur in dogs and cats?
In dogs, hypothermia occurs when the body temperature falls below 37.5 °C, in cats below 38.0 °C. - Which animals are particularly at risk for hypothermia?
Particularly at risk are very young and old animals, small breeds with unfavorable surface-to-volume ratios, short-haired breeds, underweight animals, and animals with pre-existing conditions such as hypothyroidism or heart failure. - How can I correctly measure my pet’s body temperature?
The measurement is taken rectally with a digital thermometer, which should be left in the anus for at least one minute. The thermometer should be coated with Vaseline or a water-soluble lubricant beforehand. - Is shivering in cold weather always a sign of hypothermia?
Not necessarily. Shivering is initially a normal compensatory mechanism for heat production. However, if the shivering persists or is accompanied by other symptoms such as lethargy, it may indicate hypothermia. - Can I give alcohol to my hypothermic pet to warm it up?
No, absolutely not! Alcohol dilates peripheral blood vessels and can lead to further heat loss. Additionally, alcohol is toxic to animals. - Why shouldn’t a hypothermic animal be warmed up too quickly?
Warming up too quickly can lead to the “afterdrop” phenomenon, where cold blood from the periphery flows back to the heart and further lowers the core temperature. Additionally, reperfusion injuries and dangerous cardiac arrhythmias can occur. - Can hypothermia cause long-term damage?
Yes, especially in cases of severe hypothermia, organ damage to the kidneys, liver, brain, and other organs can occur. Neurological deficits can also persist as long-term effects. - How can I prevent hypothermia in my pet?
By providing adequate weather protection, adjusting walks in cold weather, using dog clothing for sensitive breeds, immediately drying off after water contact, and taking special precautions with high-risk patients. - Is hypothermia dangerous during anesthesia?
Yes, perioperative hypothermia can lead to prolonged recovery times, increased risk of infection, coagulation disorders, and cardiac arrhythmias. Therefore, warming systems are used in modern veterinary medicine during surgeries. - When should I take my hypothermic pet to the vet?
A veterinarian should be consulted for any suspected hypothermia. It is urgently necessary when body temperatures are below 35°C, if there is altered consciousness, breathing problems, or if the animal does not respond to simple warming measures.
Literature
- Tischer, A.: The effect of heat and moisture exchangers on intraoperative temperature development in dogs and cats. Inaugural dissertation FU Berlin, Berlin 2010
- Löwe, G. and Löwe, O. (2021). Emergencies in Dogs and Cats – A Veterinary Guide. Kynos-Verlag. 208 p.
- Brodeur A, Wright A, Cortes Y. Hypothermia and targeted temperature management in cats and dogs. Journal of Veterinary Emergency and Critical Care. 2017;27(2):151-163.
- Oncken AK, Kirby R, Rudloff E. Hypothermia in critically ill dogs and cats. Compendium on Continuing Education for the Practicing Veterinarian. 2021;23(6):506-521.
- Silverstein DC, Hopper K. Small Animal Critical Care Medicine. 2nd ed. St. Louis, MO: Elsevier; 2022.
- Mazzaferro EM. Perioperative hypothermia in small animals. Veterinary Clinics of North America: Small Animal Practice. 2023;53(1):95-107.
- Plunkett SJ, McMichael M. Emergency procedures for the small animal veterinarian. 4th ed. London: Elsevier; 2023.
