Hypothermia in dogs: signs, first aid and treatment

Overview

An adult dog's normal temperature is usually around 38–38.5°C. A core temperature below 37.5°C is used as the threshold for hypothermia in adult dogs. However, the temperature of the skin or ears does not always reflect the temperature inside the body. Simply feeling the nose or ears is therefore not a reliable way to assess body temperature.

Hypothermia affects the core temperature of the whole body. Frostbite is local tissue damage caused by cold. It most often affects the ears, paws and tip of the tail. The full extent of the damage may only become apparent over the following few days.

A newborn puppy's normal rectal temperature is 35–37.2°C during the first week of life. In weeks 2–3, the normal rectal temperature is 36.1–37.8°C. The reference range does not rise to 37.2–38.3°C until week 4.

Causes

More heat is lost than produced

The hypothalamus in the brain controls body temperature regulation. In the cold, small arteries in the skin narrow, helping to retain heat inside the body. Involuntary muscle contractions, or shivering, produce extra heat. Curling up reduces the body surface exposed to the cold.

Prolonged cold exposure can overwhelm temperature regulation even if it works normally at first. A dog that stays wet becomes chilled particularly in cold water or after it stops exercising. Heat also leaves the body through contact with a cold surface. Air movement and evaporating water can increase heat loss.

Illness can also cause hypothermia

In secondary hypothermia, heat production or temperature regulation fails even in a warm environment. Causes include circulatory shock, low blood sugar and an underactive thyroid. A severe infection, severe Addison's disease or anaphylaxis can also lower body temperature. Heavy blood loss reduces the body's ability to stay warm.

Risk factors

Small dogs lose heat more readily in relation to their weight than large dogs. Puppies cannot regulate their body temperature as effectively as adult dogs. Their limited body fat makes them more sensitive to cold. Older, underweight and otherwise unwell dogs are particularly vulnerable to becoming chilled.

A short or thin coat offers less protection from cold than a dense double coat. Previous acclimatisation to cold conditions also affects a dog's tolerance. Prolonged anaesthesia or surgery increases the risk of heat loss. An anaesthetised dog cannot increase heat production by moving or shivering in the usual way.

A newborn puppy's temperature regulation remains immature until about 4 weeks of age. Its small energy reserves can run out quickly if it cannot suckle. Even a short period without feeding can then cause low blood sugar.

Typical symptoms

The first signs that a dog is struggling with the cold may appear in its posture and movement. A dog that feels cold may suddenly become restless or vocal.

• Your dog shivers as its muscles try to produce more heat.

• Your dog lifts its paws off the cold ground.

• The tail is tucked between the legs or the back becomes arched.

• Your dog is reluctant to carry on walking as usual.

• Movement becomes clumsy and your dog may seem confused.

• Your dog's gums may become paler than usual.

• The heartbeat may become slow and irregular.

In severe hypothermia, shivering may stop altogether. This means a protective response that helps produce heat is failing. Consciousness may deteriorate as far as coma, a state of deep unconsciousness.

Complications and consequences

Cold disrupts circulation and breathing

At first, the body may respond to cold with an increased heart rate. As cooling continues, however, the heart rate slows considerably. Abnormal rhythms may develop in the upper or lower chambers of the heart. The most serious consequence is cardiac arrest.

Slower breathing can impair ventilation of the lungs and eventually lead to respiratory arrest. Coughing and other protective airway reflexes may weaken, increasing the risk of aspiration, when foreign material enters the airways. Hypothermia can also impair blood clotting. In a dog losing blood, hypothermia, increased blood acidity and poor clotting can make one another worse.

The kidneys, metabolism and recovery may suffer

Cold can increase urine production and reduce circulating blood volume even when a dog is dehydrated. Water and electrolytes, the body's salts, may be lost in the urine. Kidney and intestinal damage are also possible. Drug breakdown can slow down, delaying recovery from anaesthesia. Wounds may heal more slowly in a hypothermic patient.

Cold can impair platelet function and slow the formation of the initial clot. The body's ability to fight infection may also weaken during hypothermia. Slow breathing may fail to remove carbon dioxide normally, further increasing blood acidity.

Diagnosis at the vet

Measuring temperature and assessing vital functions

A dog's body temperature is usually measured rectally. In hospital, core temperature can also be measured in the oesophagus of an anaesthetised or unconscious dog. Rectal temperature may differ from the actual core temperature by about 0.4°C.

In classifications of hypothermia, a core temperature of 32–37°C has been considered mild. Moderate hypothermia means a core temperature of 28–32°C. A temperature below 28°C is classified as severe hypothermia. Do not wait until a classification threshold is reached before seeking help: suspected hypothermia already needs immediate assessment.

The vet checks that the airways are clear and assesses circulation and breathing. An ECG can monitor the heart's rhythm. A severely chilled dog's breathing and pulse may be so weak that they are difficult to detect. A cold dog that appears lifeless therefore needs careful assessment.

The vet also looks for injuries and open wounds through which heat can escape. Blood tests can identify problems with blood glucose, electrolytes and acid–base balance, among other things. Clotting test results may look better than the actual situation because routine laboratory tests are performed at 37°C.

Treatment

Dry your dog, insulate against cold and seek care

Move your chilled dog into a warm, dry place. Towel-dry a wet coat. Put dry blankets underneath and over your dog to reduce heat loss. Increase the room or car temperature gradually. Continue first aid on the journey to the vet, where your dog's condition will be checked.

Offer lukewarm water only if your dog is awake and able to drink independently. Handle a severely chilled dog calmly and gently, as vigorous handling may trigger an abnormal heart rhythm. Hot-water bottles and hot grain-filled heat packs can cause burns.

Hospital care supports circulation and controlled warming

The treatment method depends on the severity, duration and cause of hypothermia. Passive warming means retaining the heat the dog produces, for example with dry insulating blankets. Active external warming uses a controlled heat source, such as a forced-air warming blanket. Supplemental oxygen can help supply the tissues when breathing or circulation is impaired.

Warmed intravenous fluids help restore circulating blood volume and correct low blood pressure. A dog in shock is warmed slowly while receiving fluids until its rectal temperature exceeds 36.5°C. If circulation is inadequate, active external warming is started only after circulating blood volume has been sufficiently restored.

Otherwise, marked widening of peripheral blood vessels can lower blood pressure and cause rewarming shock. Cold blood returning from the limbs to the core can also briefly cause a further fall in core temperature. Active warming therefore initially focuses on the trunk rather than the limbs.

Severe hypothermia needs continuous monitoring

Severe cases may need internal warming, for example using warmed fluids to flush body cavities. These are hospital procedures with their own risks of complications. The rise in temperature is monitored to prevent overheating. Active warming of an adult dog may be stopped at around 37–37.5°C as its own temperature regulation starts to recover.

Emergency care first stabilises breathing and circulation and starts controlled warming, followed by treatment of any underlying disease identified. Medicines are chosen cautiously because chilling can slow their elimination from the body.

A chilled newborn needs care suited to its age

A newborn puppy is warmed slowly, usually over 30–60 minutes, following the vet's instructions. Tube feeding starts only once the puppy has reached a normal body temperature. Hypothermia can stop intestinal movement and increase the risk of milk reflux and aspiration.

Prevention

Adjust the length of walks to your dog's cold tolerance and watch its behaviour. A dog with a thin coat, a small dog or an older dog may benefit from a warm coat. Dry your dog if it gets wet and carry a towel on outings in cold weather. Do not leave your dog waiting in a cold car after a walk.

Avoid walking on frozen bodies of water, as thin ice may give way beneath your dog. At home, provide a warm bed away from draughts. During surgery and anaesthesia, insulating blankets and paw covers can reduce heat loss.

A heating pad can burn a newborn puppy if it cannot move away from a surface that is too hot.

Important for dog owners

When calling the emergency vet, explain how long your dog was in the cold, whether it got wet and whether it has received any medicines or recently had an anaesthetic. Record the temperature, when you measured it and the first aid you have given. Keep watching your dog's breathing, responses and movement. Keep dry blankets and a thermometer within easy reach. After treatment, check whether your dog needs another examination if it becomes tired again, eats poorly or later develops changes to its paws or ears.

A dog that has become wet in the cold or is unwell should be examined even if it seems brighter after first aid.

Frequently asked questions

Is it a good sign if my dog stops shivering?

Not necessarily: a severely chilled dog may stop shivering altogether. Shivering normally produces heat through muscle activity. If your dog is still cold or becomes sleepy, it needs first aid and immediate veterinary assessment.

Can hypothermia happen indoors?

Yes, if illness or another factor disrupts heat production or temperature regulation. Possible causes include circulatory shock, low blood sugar and certain types of poisoning. Anaesthesia and room-temperature fluids given in hospital can also contribute to cooling.

Can I warm my dog with a hot-water bottle?

A hot-water bottle can burn a chilled dog's skin. Safe first aid starts with thoroughly drying a wet coat and putting dry blankets underneath and over your dog. Increase the surrounding temperature gradually while arranging veterinary care.

Can I give a hypothermic dog water?

You can offer lukewarm water to a dog that is awake and able to drink independently. Severe hypothermia may weaken protective airway reflexes and increase the risk of aspiration. Do not force a dog with reduced consciousness to drink; it needs emergency veterinary care.

How can I measure my dog's temperature reliably?

A dog's temperature is usually measured with a rectal thermometer. Feeling the nose, tongue or ears does not replace measurement. There may be a considerable temperature difference between the skin and the inside of the body, so touch alone can be misleading.