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Anesthesia and Pets

Q: What is the difference between sevoflurane and isoflurane?

A: Both sevoflurane and isoflurane are inhalant anesthetics routinely used in both human and veterinary medicine. The main benefits of sevoflurane include more rapid change of anesthetic depth and less irritation to the respiratory tract. The general reputation of sevoflurane as being “safer” comes from the rapid changes in anesthetic depth that can be obtained with sevoflurane.

When using isoflurane, a pet may make take 10 minutes or longer to become more or less anesthetized after an adjustment. That generally requires a veterinarian to select a plane of anesthesia he knows for certain will be deep enough for the surgery. That often means the pet is deeper than the minimum required level of anesthesia.

With sevoflurane, adjustments take only a minute or two. Because of the rapid ability to adjust, it is possible to keep a patient just barely deep enough for the procedure. If reflex signals indicate the anesthesia needs to be increased, it only takes a minute or so and does not significantly delay the procedure or increase the time under anesthesia. It is also comforting to know that if there is a problem, the sevoflurane will wear off much more rapidly than isoflurane.

In actual practice, it would not be correct to say that sevoflurane is safer than isoflurane. Most veterinarians have safely used isoflurane for years. It is generally safer for a doctor to use an anesthetic drug he knows well than that is unfamiliar to him. I have used both in my practice for several years. I have come to develop a strong preference for the sevoflurane. In my hands, pets’ blood pressure can be maintained closer to normal throughout anesthesia and patients wake up much more quickly when I’m finished. Because I can quickly adjust the depth of anesthesia, I also do a better job at controlling unexpected pain when using sevoflurane.

Q: Why not use sevoflurane on every pet?

A: To tell you the truth, I am getting close to this right now. The only time I use isoflurane is for spays and neuters on healthy pets. Every other general anesthetic procedure in my practice gets sevoflurane. The only reason I use isoflurane for spays and neuters is cost. A bottle of isoflurane costs me $25. The same bottle of sevoflurane costs me $250. Since many people choose their spay or neuter surgeon based on cost (poor decision), veterinarians are under pressure to find ways to keep the procedures as inexpensive as possible. Isoflurane is a safe way for me to reduce the cost of the procedures with minimal impact to the patient. For anesthesia on an older pet or one with a medical problem, I advocate sevoflurane in almost all cases despite the increased cost.

Q: Why do veterinarians run blood tests before anesthesia?

A: This is another way we can minimize risk. Every patient, human or veterinary, should have a thorough physical examination and routine laboratory screening tests before anesthesia. These tests help the doctor compile a complete picture of a patient’s health status. Even slight abnormalities may necessitate a different choice of drugs, different fluid rate, or even an alternate procedure. For example, in humans it is well established that a low serum albumin is the single strongest predictor of post-operative mortality for non-cardiac surgery. If your pet’s albumin is low before anesthesia, don’t you want your veterinarian to know? No doctor likes to be surprised by adverse events during an anesthetic episode. We would much rather have the information in advance that will allow us to formulate the safest possible anesthetic experience for our patient

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