Anesthesia Types

What exactly is general anesthesia?

General anesthesia is defined by Webster's Dictionary as a loss of sensation affecting the entire body accompanied by a loss of consciousness.  That is a pretty all encompassing definition.  At All Feline Hospital, the vast majority of our surgical procedures are performed with general anesthesia.  This means that your cat will be completely asleep for the procedure, and will wake up afterwards.

What are the different types of general anesthesia?  Do I get to choose for my cat?

We offer 2 primary types of general anesthesia for most procedures.  Injectable and gas anesthesia.  For select routine procedures on young cats, you do get to choose which type of anesthesia you would like to have used.  For older cats, or for more advanced lengthy procedures, we will only use gas anesthesia.

Injectable anesthesia that we use consists of a drug called ketamine which is injected into the muscle.  This will result in about 30-60 minutes of complete unconsciousness with a gradual waking up that can take anywhere from 6 to 24 hours.  Ketamine also is a dissociative drug, which means that even if your cat were to feel pain, which we do our best to avoid, they don't associate it with themselves, and it does also have some pain blocking effects as well.  For more painful procedures such as declaws, ketamine works very well at helping to prevent pain from being felt in the first place.  Ketamine does have some brief discomfort associated with its injection, but it is fairly inexpensive, which enables us to keep our costs low for routine procedures that do not take long to perform.  Ketamine does have some cardiac effects, and can lower what is called the seizure threshold, so we will only use it on young healthy cats.  In addition, it is a rare side effect, but ketamine can potentially change a cat's personality, sometimes temporarily, sometimes permanently.  Once ketamine is in your cat's system, we cannot reverse it.  So, if there is a complication, such as not breathing during surgery, we have to maintain supportive care until the ketamine starts to wear off.

We have two different types of gas anesthesia that we will use in cats.  Sevoflurane and isoflurane.  Sevoflurane is a very fast acting gas anesthesia which will result in a quick loss of consciousness and a quick return to consciousness.  However, it is extremely pricey.  Isoflurane takes just a little longer to both lose consciousness and regain consciousness, but it is a little more cost effective.  Therefore, we will usually use sevoflurane to induce anesthesia, and then switch to isoflurane to maintain anesthesia during the procedure.  Both gasses are very commonly used in human medicine.  The advantage of gas anesthesia is that we maintain control of the depth of the anesthesia, and can deepen it or lighten it as needed during a procedure.  If there is a complication, we can wake up the cat almost immediately if it is safe to do so.  While there is no 100% safe anesthesia, gas anesthesia has the fewest risks associated with it.

What is local anesthesia?

Local anesthesia consists of an injection given under the skin where the nerves are most plentiful to block specific nerve conduction for a short period of time in a small area.  The two local anesthetics that we use most often at All Feline Hospital are lidocaine and bupivicaine.  Lidocaine takes about 5 minutes to block nerve conduction and lasts for about 10-15 minutes.  Bupivicane takes about 20-30 minutes to block nerve conduction, but can last for 6-8 hours.  Cats are extremely sensitive to local anesthesia injections, so we use the lowest effective doses to avoid systemic side effects.  We most commonly use these drugs as adjunct pain control for painful surgeries such as declaws.  However, we will occasionally use local anesthesia for very minor skin surgeries for cats that are not good candidates for general anesthesia.  Since local anesthesia can sting quite a bit when injected with no other pain blocking, such as general anesthesia, if we are using local anesthesia on a concious cat we will buffer it with sodium bicarbonate.  With the buffering, most cats don't seem to notice that anything is being injected under the skin.