Chris Kouwenhoven

Is anesthesia safe?

Today we have a question from Colette of Vancouver, WA, USA., who asks "what are the common anesthetics used for cats and are they safe". Great question, Colette, and since so many of our readers will take their pets to their family veterinarian for surgery at some time, it should be of interest to everyone. You ARE planning to take your pet in for spaying/neutering aren't you?

There are two basic forms of anesthesia used on humans and animals: local and general anesthesia. Local anesthesia is what your dentist uses when he or she numbs your mouth prior to drilling. You know, when you end up with a wooden tongue and drool all over yourself trying to rinse and spit! The purpose in local anesthesia is to block pain sensations from a specific area by injecting a local anesthetic drug into the nerve(s) serving the area. Commonly, xylocaine or a similar agent is used for local anesthesia.

Local anesthesia is significantly safer than general anesthesia unless the patient is sensitized to the drug which results in an allergic reaction. Since continued use of local anesthetic agents on a particular patient is unusual, such sensitization is very uncommon. Naturally, there are limitations on what procedures may be accomplished under local anesthesia. Generally speaking, only superficial surgeries, such as the removal of small skin growths or a tooth extraction, are suitable for this type of anesthesia.

The other class of anesthesia is general. In this type the patient is placed in a state of deep sleep in which pain sensations are not perceived by the brain. General anesthesia is suitable for internal surgeries, such as ovarohysterectomies (spay) or repair of a fracture. Sometimes a muscle relaxant is also given to facilitate the surgeon's work.

In terms of how the general anesthesia is administered to the patient, there are two methods.

In both methods of general anesthesia, a tube is placed in the trachea (windpipe) of the patient after a tranquilizer is administered. This tube, called an endotracheal tube, has a cuff around the open tube which, when inflated, prevents any foreign agents from going into the lungs. Such material in the lungs often results in a very serious type of pneumonia, so the placement of the endotracheal tube is very important.

Injectable anesthetic agents are administered subcutaneously, intramuscularly or intravenously. The route for injectable agents depends on the particular drug, the type of anesthesia desired and the species of animal. Commonly ketamine is used, especially in cats, although there are many other types of injectable agents available.

The other method of achieving general anesthesia is via inhalation anesthesia. In this form, the inhalation anesthetic agent is introduced through the endotracheal tube directly to the lungs where it is absorbed into the bloodstream, resulting in general anesthesia.

Since the inhalation type of general anesthesia is rapid acting and is quickly metabolized by the body, the level of anesthesia is easier to control and it is therefore a safer choice in a critical patient.

However, in the vast majority of cases, the use of injectable agents is much more common. The patient is easier to work on with the injectable form since there is no connection to an external machine. The surgeon does not have to worry about the operation of the machine and can concentrate on the surgery at hand. The type of anesthesia employed is a decision your veterinarian makes based on the type of surgery, the condition and species of the patient and her or his experience.

General anesthesia is somewhat dangerous because you are introducing a potent drug into the patient's body which acts on the brain. However, your veterinarian is well trained and experienced in using these agents and only very rarely do patients have problems with general anesthesia.