Hypothermia
Dogs don't get dangerously cold very often because they have a strong shiver reflex.
Shivering increases the body's metabolism and generates heat. Their fur is also a great insulator. It traps warm air next to the skin, keeping pets' internal temperature in the normal range of 99-102.5 degrees. As a result, they're less likely than people to suffer from hypothermia, or low body temperature.
Things change when there's a lot of wind or the dogs fur gets wet, and especially when they spend more time outside than their bodies are designed to handle. As body temperature drops, so do essential functions such as breathing and heart rate. Pets with mild hypothermia, in which body temperature is between 95 and 99 degrees, will shiver, tremble, act sleepy, and be cold to the touch. Most pets with mild hypothermia will recover within an hour with the help of first aid.
Pets with moderate hypothermia have temperatures in the range of 90-95 degrees. They can be treated with first aid at home, but they may take longer to recover than those with mild hypothermia. After home therapy, a pet with moderate hypothermia needs to see a vet the same day. If his temperature doesn't rise after first aid, the dog needs to get to a vet Immediately.
Severe hypothermia can be deadly. Pets stop shivering when their body temperatures drop to around 90 degrees, and without shivering, it's nearly impossible for them to warm up without extra help. With severe hypothermia (body temperature about 90 degrees) pets lose consciousness, their organs begin to fail, and the heartbeat and breathing nearly stop completely. Severe hypothermia requires emergency first aid and immediate vet attention.
Dogs whose temperature has dropped to 90 degrees for longer than 30 minutes need to be rewarmed from the inside out, using special techniques that your vet is trained to perform.
Trying to rewarm the dog yourself in this situation is dangerous- Call Your Vet!
The signs of hypothermia are: violent shivering followed by listlessness and apathy, a rectal temperature of below 97 degrees, and finally a collapse and coma.
Treatment:
Wrap your dog in a blanket or coat and carry him into the house. If the dog is wet (having fallen into icy water), give him a warm bath. Rub him vigorously with towels to dry his skin.
Warm chilled dogs by applying warm water packs to the armpit, chest and abdomen. The temperature of the packs should be that of a baby bottle (warm to the wrist). Continue to change the packs until the rectal temperature reaches 100 degrees F. Warming with a hair dryer works well too.
As the dog begins to move about, give him some honey or glucose (four tablespoons of sugar added to a pint of water).