"Shock and awe" is more than a military tactic - it's a good description of a potentially deadly allergic reaction that occurs in all types of mammals and, without prompt emergency treatment, is fatal.
Anaphylaxis, commonly known as "anaphylactic shock," is a rare but rapidly-developing allergic reaction that results in respiratory failure, heart failure and death. It's most often caused by an allergic reaction to a bite from a stinging insect or snake, or after ingesting a certain food. It can also be brought on by vaccines, antibiotics and select hormones and medications.
Symptoms of anaphylaxis come on quickly, usually within an hour of exposure, and usually include diarrhea, vomiting, shock, seizures, coma and sudden death. In the early stages of a reaction, most dogs will have a racing heartbeat but a weak pulse, and will be restless and excitable. Also, their gums will be very pale and the limbs will feel cold. This is because the reaction pulls fluid from the bloodstream, making the blood thicker and less able to travel to the dog's lower limbs and other extremities. The liver and gastrointestinal system are also hard-hit by shock-related blood and oxygen deprivation.
Prompt emergency treatment is a must if your dog is to survive this deadly reaction. The first and most crucial step is that the dog be given a shot of epinephrine, preferably within the first few minutes. Normally, affected animals then require a combination of intravenous (IV) fluids, oxygen and other medications to help their system recover. The dog also may benefit from follow-up therapy with antihistamines and corticosteroids, to help control the immune system's response to the allergen.
There's no real way to predict which animals will have a reaction to which substance until one occurs. Often anaphylaxis will not result until a dog has been exposed to an allergen multiple times. So, if your dog has had a prior reaction to a vaccine, food or insect bite (in the form of swelling, hives or vomiting), then that substance should be avoided whenever possible. If the reaction was to a vaccine, your veterinarian can help determine if that particular vaccination can be safely administered under controlled circumstances, or whether a different type of vaccine should be used in the future.
Owners who vaccinate their own pets or who know their pet is allergic any particular substance or insect should keep an "epi-pen" on hand. This is a pre-filled, sterile syringe containing a single dose of epinephrine, and is available from your veterinarian. If the animal has a severe reaction, you can inject the dose of epinephrine and then seek emergency help. Epi-pens are particularly recommended when a dog is allergic to insect bites; be sure to take the pen along on any long walks or hikes with your pet.