Anesthesia side effects in cats depend on the type of sedation used for the surgery. Before your cat undergoes surgery, your vet will conduct blood and urine tests, and possibly an X-ray, to ensure your cat doesn't have an underlying condition that could rule out a particular anesthetic. Your vet will tell you not to feed the cat for about 12 hours prior to surgery, to avoid the cat vomiting as he goes under or comes to. The vomit could go into his lungs, resulting in suffocation or aspiration pneumonia. The most common side effect of anesthetics is post-surgical drowsiness, which might last a day or so.
Acepromazine for Cats
Although not an anesthetic, the tranquilizer acepromazine is commonly administered to cats prior to surgery. It conjunction with anesthetics, it aids in achieving complete sedation. The effects of acepromazine lasts six to eight hours. Side effects include lowered blood pressure, which can increase the cat's heart rate. Cats with cardiac disease, anemia or epilepsy should not receive the drug. If you notice your cat's third eyelid appearing several hours post-surgery, that's a normal occurrence. As the drug wears off, the third eyelid, or nictitating membrane, should disappear.
Ketamine as an Anesthetic
If your cat is young and healthy and undergoes a relatively minor procedure, your vet might chose to use ketamine as an anesthetic. Injectable ketamine puts a cat completely "out" for about an hour, although he won't necessarily completely come back to normal for up to 24 hours. Cats with heart disease or epilepsy should not receive ketamine. The amount of ketamine given to a cat depends on the animal's weight. Ketamine does have one potential, albeit rare, side effect. It can change Kitty's personality, either temporarily or permanently.
In older felines, or for more complex operations, your vet will use a gas anesthesia of the same type used in human surgeries. Common anesthetics used in felines include isoflurane and sevoflurane. How much anesthetic your cat receives depends on his weight, age, general health and any breed-related complications. Years ago, cats more often died from a reaction to the general anesthesia than they do today. That doesn't mean it can't happen, but it's rare. Possible but uncommon side effects to general anesthesia include blindness, liver or kidney failure, cardiac problems, seizures or blood clotting issues. While your cat is under anesthesia, the operating room staff will monitor his blood pressure, heart rate and heartbeat, breathing, body temperature and the oxygen in his blood.
If your cat comes home the same day as surgery, as often happens with a neuter or spay operation, keep him in a quiet, safe place where he can recover. Your vet will inform you when you can start feeding your pet. It's not unusual for a cat recovering from surgery not to have a bowel movement in the first 24 hours, but let your vet know if he doesn't pass stool beyond that period. While your cat might seem drowsy, he shouldn't be completely knocked out. If you can't get him up, call your vet immediately.