Why It’s Important to Starve Your Pet Before Surgery

If your pet vomits up food or has gastric reflux during anesthesia and then breathes it into their lungs, there’s a risk of aspiration pneumonia.

Your dog may beg for food before surgery, but it’s best to bring them into the clinic with an empty stomach. By: MISS_SUMMER

It started off like any other dental: Mac had 4 bad teeth that needed to come out. His pre-GA bloods were fine, he was nicely chilled after the pre-med injection and inducing anesthesia went smoothly.

Indeed, sorting the first side of his mouth went smoothly. The rotten teeth came out easily, and the rest polished up like ivory. It was when we turned Mac to rest on his other side that it happened.

A gush of yellow-colored fluid came flooding out of his nostrils. Needless to say, this isn’t normal. To work out what was happening, the vet tech collected a sample to run tests.

The fluid was acidic, around pH 5.4, a similar pH to stomach acid. The penny dropped. This was a case of severe gastric (or acid) reflux.

For the remaining time Mac was under anesthetic, there was a steady trickle of fluid from the stomach out through his nostrils. It was as if he’d had a belly full of water ahead of the anesthetic.

A Controlled Recovery

Mac woke uneventfully, but possibly with a bit of a headache. This was because it was necessary to keep his head much lower than his stomach while he was waking. This allowed fluid in his gullet to drain safely out of his mouth rather than inhaled down into his lungs.

I also gave Mac intravenous antacid medication and antibiotics to reduce the risk of complications down the line.

Vomiting Under Anesthesia Is Dangerous

When under anesthesia, the patient cannot swallow.

If the stomach contracts and forces vomit up into the mouth, the dog or cat can’t swallow it back down into the stomach. If they don’t have a tube in their airway, there’s every chance of inhaling vomit down into the lungs.

Inhaled vomit causes 2 problems:

  1. It blocks the airway, causing the patient to suffocate.
  2. Stomach acid in the lungs can set up serious pneumonia.

Either way, it’s a problem best avoided.

Fortunately, vets are fully aware of these risks and take steps to ensure the patient is safe, even if vomiting happens.

Cats under anesthesia are also at risk for aspiration pneumonia. By: woodsilver

Avoiding Complications During Anesthesia

Starve Ahead of Anesthesia

Cats and dogs should be starved the night before their procedure (unless otherwise advised by their vet). With an empty stomach, even if the patient retches while asleep, there won’t be much to bring up.

For most healthy patients, it’s OK to leave water down overnight, but remove it first thing (around 7 a.m.) for surgery later that morning.

A Tube in the Throat

One precaution is to place a special tube into the patient’s windpipe during the anesthetic. This keeps the airway open and allows the pet to be kept asleep with a gaseous anesthetic.

Another benefit is the tube seals off the airway, so that stuff in the mouth can’t physically get down into the lungs.

Throat Packs

Mac was having a dental, which means water from the de-scaler in his mouth. As a matter of routine, we insert throat swabs to protect the airway from water and debris.

Tilted Table

And finally, the patient lies on an angled table, with their head lower than their stomach. This means any vomit should drain out of the mouth under gravity, and reduce the risk of it entering the lungs.

This was why the stomach acid leaked out of Mac’s nose; it tricked downhill rather than pooling at the back of his throat.

Vets take many precautions to keep dogs from breathing in harmful gastric acids during anesthesia. By: Pixabay

What Happened With Mac

I suspect the problem happened because Mac and had a long, deep drink of water before his trip to the surgery on this hot day. When he had the anesthetic, he still had a belly full of water.

Under the anesthetic, the muscles that stop food from heading the wrong way out of the stomach relax. This meant water and stomach acids leaked out into the gullet (esophagus) in such quantity that it leaked out of his nose.

All the protocols in place meant he stayed safe, despite this mishap.

However, gastric reflux does carry a risk of complications. To reduce these, Mac had some pre-emptive treatment:

  • Intravenous antacids: The tissue of his gullet may well be sore and inflamed after contact with stomach acid. Therefore, making the stomach acids less strong helps that sore tissue heal.
  • Antibiotics: In case of fluid getting into his lungs, Mac had a course of antibiotics to reduce the risk of aspirational pneumonia.

Starved animals can still get gastric reflux under anesthesia, but there’s less risk of serious complications.

Under an anesthetic, everything relaxes, including the valves that seal off the stomach. It’s not unusual that a little stomach acid leaks out into the gullet when the animal is asleep.

If the procedure is short, then the natural defenses of the esophagus keep the acid away from the delicate tissue.

However, for longer procedures, the pet can sometimes experience a condition akin to heartburn. The signs include a poor appetite post-surgery, drooling and retching after eating. This is usually easily treated with antacid medication.

Watch this fascinating behind-the-scenes surgery on a dog’s ear:

The Take-Home Message

Take starving your pet ahead of surgery seriously. While the odd treat isn’t going to hurt (indeed, there’s now evidence a small treat helps mop up stomach acid and reduces acid reflux) a full stomach — whether food or water — is a bad idea.

But the vet has your back. We have protocols in place that anticipate problems such as gastric reflux, so there’s less chance of harm. However, let’s not make life more difficult or stressful than it has to be, so be sure to follow those pre-op instructions carefully.

And know that these rules apply to cats or dogs. Rabbits or guinea pigs should never be starved for surgery, but that’s another article for another day.


This pet health content was written by a veterinarian, Dr. Pippa Elliott, BVMS, MRCVS. It was last reviewed Aug. 17, 2018.

Dr. Pippa Elliott, BVMS, MRCVS

View posts by Dr. Pippa Elliott, BVMS, MRCVS
Dr. Pippa Elliott, BVMS, MRCVS, is a veterinarian with nearly 30 years of experience in companion animal practice. Dr. Elliott earned her Bachelor of Veterinary Medicine and Surgery from the University of Glasgow. She was also designated a Member of the Royal College of Veterinary Surgeons. Married with 2 grown-up kids, Dr. Elliott has a naughty puggle called Poggle, 3 cats and a bearded dragon.

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