How Long Should Your Cat Fast Before Anesthesia?

Guidelines versus actual practice.


For healthy adult cats about to undergo an operation, the American Animal Hospital Association now recommends a 4- to 6-hour fast prior to anesthesia. The organization suggests even shorter pre-surgical fasts for cats younger than 2 months of age and cats with diabetes, who need to eat their food at specific times to pair with their insulin injections.

The American Association of Feline Practitioners, for its part, recommends a pre-anesthetic fast of 3 to 4 hours “at the clinician’s discretion.” Yet a common veterinary practice is for clinics to tell their clients, “no food after midnight” (although water is always okay). That means if the surgery is going to take place later than noon, the cat will have to wait longer than 12 hours to eat. Why do so many veterinary clinics advise “nothing after midnight” when the latest guidelines do not square with that advice?

The whys and wherefores of anesthesia protocols

The reason cats have to fast before anesthesia at all is that stomach contents can be vomited up to the mouth while a cat is unconscious under the anesthetic drugs and then migrate down the trachea and, from there, to the lungs. That sometimes leads to aspiration pneumonia, which can be deadly. Stomach contents can also be regurgitated into the esophagus. That may result in a stricture, or narrowing, that heals with significant scar tissue, meaning food can’t easily pass. If the esophagus can’t be ballooned open, the cat may have to be fed with a stomach tube for life. Such complications are rare, but they do occur.

Most cats are likely safe from stomach contents going to the wrong places after just 6 hours of fasting before anesthesia induction, but protocols are slow to change. “It always takes a while for new guidelines to percolate into actual practice,” says Tufts veterinary anesthesiologist Alicia Karas, DVM.

There’s more to it than that, however. In a number of veterinary practices, particularly large ones, it’s virtually impossible to say exactly what time a planned surgery will occur. “It’s very difficult to schedule OR [operating room] time,” Dr. Karas says. “We have a pretty good idea how long an operation will last,” she explains, “but there are complications. It’s not like they’re all easy spays and neuters. Timing can be thrown off tremendously even by something like not being able to get an IV line into a cat. We had one cat recently — every vein was ruined by IV anti-seizure meds. So his surgery was held up.

“Or a surgeon comes in and is supposed to do two knee surgeries and one bladder surgery. But there’s an emergency. A cat swallowed a needle and thread, and it’s poking through his stomach. That can’t wait. Or something is bleeding into a cat’s abdomen. So all of a sudden the knee the surgeon was going to do starting at 8:30 is pushed off, and then we actually have no idea of who’s going to go when. Some cats may be pushed up while others are pushed back. A bomb is dropped into the schedule almost every day.”

The toll fasting takes

It’s hard for cat “parents” to see their pets go hungry after more than 12 hours of not eating, with the animal not understanding why she can’t get breakfast the morning of the surgery, and not even understanding that she’s going for surgery. But it’s often not as bad as it may seem, Dr. Karas says. “Let’s say you feed your cat at 6 pm, which many people do,” she comments. “By 6 am the next morning, the cat has undergone a 12-hour fast. It happens every single day. So if you give your cat an extra meal at, say, 11 o’clock the night before an operation and the surgery doesn’t occur until 2 the next afternoon, it’s only a few more hours tacked on to the usual fasting period. It’s not such a big deal.

“Animals in the wild, as well as people, can go several days without eating,” Dr. Karas points out. In fact, while a person can go only a few days without water, she can go for weeks without food. So a few extra hours for a cat is not very onerous, especially when you consider that the cat is probably nervous about being at the clinic and therefore not feeling very hungry, anyway.

In the future, as research results catch up with clinical practice, people may get different pre-surgery advice for their cats. But for now, in light of the fact that a cat is not really made to suffer by having to wait for the surgery while fasting, following the clinic’s directions is a better-safe-than-sorry route. That’s true whether the directions are to fast a pet for 4 hours or 6 or 12. Why take any risk by going around the pre-surgical protocol?

Special Cats, Special Anesthesia Protocols
Because cats with diabetes can’t go too long without food, if possible, they are always taken first at Tufts for operations (and their owners are told to inject only half their usual insulin the morning of the operation). Different health conditions often translate to protocols being tweaked to help insure a cat’s health while she is anesthetized.


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