Anesthesia for Cats
Anesthetics are drugs used to block the sensation of pain. They are divided into two categories: local anesthesia and general anesthesia.
Local anesthesia is used for surgery on the surface of the body, where it is injected into tissues and around regional nerves. It may be applied topically to mucous membranes. Local anesthetics (such as xylocaine) have the fewest risks and side effects but are not suitable for most major surgeries.
General anesthesia renders the cat unconscious. It can be given by injection or inhalation. Light anesthesia sedates or relaxes the cat and may be suitable for short procedures, such as removing a foreign body from the mouth. Inhaled gases (such as halothane, sevoflurane, and isoflurane) are administered through a tube placed in the trachea.
Combinations of anesthesia often are used to lessen potential side effects. For example, ketamine and xylazine (Rompun) are common injectable anesthetics used together for short procedures. The guideline dose of an injectable anesthetic is computed by the cat's weight. Since cats are unusually sensitive to ordinary doses of a drug such as barbiturates, veterinarians often administer the anesthetic in repeated small doses until the desired affect is obtained, rather than giving it all at once.
For gas anesthesia, the mixture of oxygen and anesthetic is balanced and the dose adjusted according to the breathing of the cat. Many factors require that the exact dosage be customized to the individual cat. Certain breeds have an increased sensitivity to barbiturates and other anesthesia, and that must also be taken into account. This may be related to structure, such as cats with short faces, or conformation, such as thin cats without extra weight or fat.
Anesthesia is removed from the cat's system by the lungs, liver, and kidneys. Impaired function of these organs can cause dose-related complications. If your cat has a history of lung, liver, kidney, or heart disease, the risk from anesthesia and surgery is increased. Cats with those problems may require less anesthetic to attain the needed depth of anesthesia or may take longer to become fully aware after anesthesia. Presurgery bloodwork is recommended to detect any such problems. Some clinics may also suggest chest X-rays, an EKG, and blood pressure evaluations, especially if your cat is geriatric.
A major risk of a general anesthetic is the cat vomiting when going to sleep or waking up. The vomitus refluxes into the trachea and causes asphyxiation. This can be avoided by keeping the stomach empty for 12 hours before scheduled surgery. If you know your cat is going to have surgery, do not give anything to eat or drink the night before. This means picking up the water dish and keeping the cat away from the toilet bowl and other sources of water, as well. If your cat has liver or kidney problems, your veterinarian may suggest leaving water available. Diabetic cats may need adjustments in their feeding schedule and insulin injections.
Your cat will also have an endotracheal tube placed into his trachea. This has a small balloon cuff to prevent any fluids from leaking into the lungs. This tube is attached to the gas anesthetic machine.
This article is excerpted from “Cat Owner’s Home Veterinary Handbook” with permission from Wiley Publishing, Inc.
Copyright © 2008 by Delbert Carlson, DVM, and James M. Giffin, MD. All rights reserved.