Anesthetics are drugs used to
block the sensation of pain. They are divided into two categories: local and
Local anesthetics are used to numb the surface of the body. They are
injected into tissue and around regional nerves. They may also be applied
topically to mucous membranes. Local anesthetics, such as xylocaine, have fewer
risks and side effects than general anesthetics, but they are not suitable for
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General anesthetics render the dog unconscious. They can be
given by injection or inhalation. Light anesthesia sedates or relaxes the dog
and may be suitable for short procedures, such as removing porcupine quills.
For prolonged surgeries or extremely painful procedures such as surgery on the
eye or orthopedic procedures, the dog may need to be kept at a deeper level of
anesthesia. This is normally done using inhaled anesthetics. Inhaled gases,
such as isoflurane, are administered through a tube placed in the dog’s
trachea. By adjusting the flow of the gas, the dog can be kept at a lighter or
deeper level of anesthesia.
The guideline dose of an injectable anesthetic is computed according to the
weight of the dog. For gas anesthesia, the mixture of oxygen and anesthetic is
balanced and the dose adjusted according to the breathing of the dog. Many
factors require that the exact dosage be customized to the individual dog.
Certain breeds have an increased sensitivity to barbiturates and other
anesthetics, and that must also be taken into account. Toy breeds and breeds
with a low percentage of body fat, particularly Greyhounds and Border Collies,
require less anesthetic per pound of body weight. This is one reason why
anesthetics should be given by someone who is trained to determine the degree
of sedation each drug produces.
Combinations of anesthetics are often given to lessen the potential toxicity
Anesthetics are removed from the bloodstream by the lungs, liver, and
kidneys. Impaired function of these organs can cause dose-related
complications. If your dog has a history of lung, liver, kidney, or heart
disease, the risk from anesthesia and surgery is increased. Presurgery
bloodwork will help your veterinarian to determine the safest drug and dose for
A major risk of general anesthesia is the dog vomiting when going to sleep or waking up. The vomitus
refluxes into the trachea and produces asphyxiation. This can be avoided by
keeping the stomach empty for 12 hours before scheduled surgery. If you know
your dog is going to have an operation the next day, do not give him anything
to eat or drink after 6 p.m. the night before. This means picking up the water
dish and keeping the dog away from the toilet bowl and other sources of water.
The endotracheal tube used to administer anesthesia has a small inflatable
balloon that helps block off the trachea and inhaling vomitus.
WebMD Veterinary Reference from "Dog Owner's Home Veterinary Handbook"