SAFE ANESTHESIA

Today a veterinarian generally uses two stages to give anesthetic to a cat.  In the first stage, an induction agent (a "preoperative cocktail") known as ketamine is given by injection to the cat in part because it is easy to use, fast acting, controls pain and sedates the cat.  In the second stage, a gas known as isoflurane is given for the length of the surgery.  

The subject of Anesthesia is a controversial one. The controversy lies mostly with ketamine and some warn against all injectables  (telezol, propofol, thiopental) including valium, another common one, which some owners, breeders and vets link anecdotally to adverse reactions in cats.  Ketamine does have side effects (such as hallucinations) and can supress the respiratory system.  Many breeders will ask that isoflurane alone be used on their cats (ie: no induction agent like Ketamine).  Injectable anesthetics can cause respiratory depression that may not be able to be reversed. Gas anesthesia is more easily monitored and controlled.

The injectable type drugs used for tranquilization are filtered out through the cats liver and kidneys. Cats in general don't drink a lot of water compared to say dogs. This makes is harder for the cats system to filter the injectables out. With the gas you take them off and 10 to 20 minutes later the cats are up and walking around. Many veterinarians feel that the gas is much safer to use than the injectables.

The truth is that a very small percentage of all cats can have an adverse reaction to anesthesia such as an allergic reaction or respiratory failure.  Many vets (and veterinary technicians) argue strongly for the overall safety of ketamine and for its usefullness as an induction agent in terms of pain control for the cat. 

Based our own research we recommend the use of isoflorane gas exclusively and no induction agents. The veterinary literature is scarce and contradictory ... some studies say it causes respiratory depression and some say the effect is negligable.   Ultimately, you will likely have to use your own good judgment based on a discussion with your vet. 

To ensure maximum safety during surgical procedures, we recommend a Pre-surgical Exam to include a complete physical exam including a routine blood serum profile to check the health of the organs (kidneys, liver, etc).

Isoflurane is one of the safest anesthetic gases.  In addition, the usual practice in most cases is for an induction agent to be used prior to administration of the isoflurane and the induction agents can cause problems for some cats.

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"The most common induction agents in cats are combinations of ketamine, a short acting injectable anesthetic, sedatives and/or pain relievers. These medications often have variable effects on individual cats, with some cats tolerating the medications with no problems at all and others having more difficulty. Ketamine appears to cause hallucinations in some cats (known effect in people) and is less commonly associated with blindness or other side effects. It can cause rises in blood pressure that are significant enough to cause problems in some cats. It is considered to be a very safe anesthetic overall, but it is not completely safe. The sedatives and pain relievers used (there are several) also have the potential to cause side effects. These agents often allow the use of lower anesthetic doses and even with some side effects are generally viewed as an improvement in safety when compared to using higher dosages of more potent anesthetic agents that are necessary without premedication of anesthetic patients. Diazepam (Valium Rx) is sometimes used as a preanesthetic agent and a small number of cats react very adversely to this medication, although liver damage is the usual finding in these cases.

Isoflurane is quickly eliminated from the body and when it is gone, the pain relieving effect of anesthesia is gone, too. I think that pets who are more susceptible to pain or who have more painful surgeries and are not given additional pain relief medications may suffer from shock or have difficulty recovering from anethesia due to the effects of pain when isoflurane is used as the sole anesthetic agent. I am not at all sure that I am right about this, but I have long suspected that with isoflurane there are more problems with underdosing it than with overdosing it, as some patients seem to be immobilized well before they have really good pain relieving effect from isoflurane. The quick elimination and potential to use low dosages are good reasons to use isoflurane but they have to be balanced against the need for additional pain relief and the need to carefully monitor patients to be sure that they are receiving adequate anesthetic effect during the procedure and following it, to ensure that reactions to pain do not lead to more severe consequences.

Oxygen is administered along with the anesthetic agents and this can cause problems if the flow rates are too high or if there is insufficient oxygentation due to problems with the anethestic equipment or if the patient doesn't maintain an adequate respiratory rate and the anesthetist doesn't notice this (or there isn't an anesthetist and the surgeon misses it). There are occasionally problems with apnea (stopping breathing) during the recovery period and on a busy day this might be overlooked, as well. We had one of these in our clinic a couple of weeks ago and truthfully it was fortunate that we caught the problem in time to prevent any serious damage to the kitten we had just neutered, as we were busy enough that we could easily have missed it on a similar day at another time. I think that problems with delivery of oxygen are the most common causes of anesthetic problems and that these often occur when the equipment and monitoring all seem to be working well, which makes it hard to figure out what happened in retrospect."

Excerpt From "Anesthesia In Cats" © 2001 Mike Richards DVM