Choosing the Safest Anesthesia (courtesy of a vet tech student via a discussion on safe dentals)

Just a quick note here on sevoflurane vs. isoflurane as this often comes up. Vets have huge debates on this ALL the time, so do vet techs -- which as you all know, I'm studying to become. Which one is better, which one is safer? It depends on who you ask. Here's what I've learned.

Sevoflurane *is* considered marginally safer for the kidneys by some vets -- but please note, the difference is marginal while the price difference is significant so if cost is a factor, consider the fact that the "safety" is only marginal. MUCH more importantly, the biggest problem with sevoflurane is that its biodegration produces toxic metabolites (inorganic flouride and hexafluoroisopropanol-HFIP to be exact), and it's unstable in soda lime, and may react with it and produce a toxic compound (compound-A) which can cause kidney damage. What does all this mean for your cat, you may well ask? It means that if a vet is using sevoflurane, they *MUST* be using a lot of it regularly and preferably have separate equipment which is cleaned and cared for very carefully. If a vet only uses sevoflurane occasionally, and more often uses isofluane, then there's a chance the equipment will not be as well tended to (due to lack of experience not negligence). That's when the above problems come into play.

RULE OF THUMB here is ... DON'T ask a vet who usually uses isoflurane to use sevoflurane for just your cat. Even though it may be marginally safer, if the vet doesn't use it regularly, the risks of equipment not being well tended to will greatly outweigh the benefits. If the vet commonly uses both types of inhalants, choose sevoflurane.

It also depends on who you ask whether premedicating with a sedative is safer. Both sevo & iso can cause profound decreases in blood pressure -- even at lower doses, therefore, some vets support the theory that presedation is safer as they inject a sedative into the cat which doesn't anesthetize but SEDATES the cat to the point that the vet can then intubate, and have a smooth induction using either type of inhalant(sevo or iso). During this time, while the cat is sedated, but not anesthetized, the vet can begin monitoring blood pressure and oxygenation saturation to ensure that nothing goes wrong. The safest form of sedation at this time -- for the kidneys and the heart -- is a drug called Propofol. But it's new and pricey and also has a very short shelf life. So, unless vets use a lot of it quickly, it expires. Some vets still prefer to use a method commonly referred to as "boxing down". This procedure involves placing a cat into an induction chamber (a see-through tank) and filling it with the inhalant. This only takes a couple of minutes .. but the vet doesn't have control over the cat's vitals during those couple of moments. It's such a short period, that it may not be important ... but it just might if the cat has a heart condition especially.

RULE OF THUMB here -- go with the method the vet has most experience using. DON'T ask a vet who regularly "boxes" down to use a pre- sedative or vice versa. They will be most comfortable with one method or another and here is where you are putting your cat's life in their hands and really have to trust them.