As a veterinary nurse, this was a topic that needed to be explained clearly and simply to pet owners. Because not only is the animal’s life at stake, it can cause much inconvenience to the veterinary work and the clients’ time when the fasting instructions are not relayed and understood well. Fasting is not as simple as “stopping food”.
How long should the fast be? Do I need to stop water too? Can I just give a teeny-tiny bit of treat? What if my pet vomits bile from the long hours of hunger? These are the most common questions I had from clients. And of course these questions will all be answered in this blog, so happy reading!
For a more fun learning experience, here is my Instagram bite-sized post!
Why is fasting important?
Blood test’s accuracy
- Bile acid test: 12-hour fast needed to give the liver time to retrieve any bile acids remaining in the blood
- ACTH stimulation (except for monitoring of treatment for hyperadrenocorticism): 12-hour fast recommended to avoid lipemia
- Potassium bromide test: 12-hour fast recommended to avoid lipemia
- etc
Prevents vomiting
A sedated or anaesthetised dog/cat relaxes, including the muscle holding stomach contents. They are more prone to vomiting, hence fasting helps to prevent it.
Prevents aspiration pneumonia
Aspiration pneumonia: lung infection/inflammation caused by breathing in stomach contents. Vomitus moves up via oesophagus and enters trachea. Cough and swallowing reflexes are absent (anaesthesia) or weak (sedation), thus unable to prevent aspiration.
In severe cases, it may result in death.
Which species cannot be fasted?
- rabbits
- guinea pigs
- rodents (hamsters, mice, rats etc)
Must NEVER be fasted or deprived of water. Their metabolism is different from cats and dogs. They require a constant source of food. Furthermore, they are unlikely to vomit under anaesthesia. When in doubt, call your veterinary clinic!
When is fasting needed?
- surgeries (e.g spay, castrate)
- dental procedures (including scaling and polishing)
- any other procedures with anaesthesia (e.g endoscopy)
- ultrasound (except for pregnant animals)
- sedation (including for radiography, wound debriding etc)
How long should the fast be?
Young puppies and kittens should NOT be fasted for long — max 1-2 hours. Reason being they are prone to hypoglycemia and dehydration which predisposes them to hypothermia.
Depending on the procedure to be done, the fasting instruction varies. For generality sake and understanding of the range of possible fasting instructions, here are some common examples for dogs and cats:
- Anaesthesia: 8-12 hours no food, 2-4 hours no water
- Sedation: 6-12 hours no food, 2-4 hours no water
- Ultrasound: 12 hours no food, water can be given
- Bile acid test: 12 hours no food, water can be given
Do I need to stop water too?
Yes for procedures that require anaesthesia or sedation.
No for ultrasound (without sedation) and blood tests that are not affected by water intake.
When stopping water, take note to not stop it for longer than 6 hours (may vary according to pre-existing conditions, age, etc) as it can cause dehydration and affect your dog or cat’s blood pressure under anaesthesia/sedation. Follow your vet’s instruction.
Most common problems when it comes to fasting
“I forgot to let the rest of my family know and they fed Fluffy this morning!”
Communicate well with everyone involved in the care of your pet.
“It slipped my mine!”
Set reminders — your calendar, reminder apps. Kindly ask your veterinary clinic to send you a reminder the day before (most clinics do already have this system in place).
“I didn’t completely understand the fasting instructions.”
When in doubt, ask politely.
“I think I removed Brownie’s bowl last night. At least I think my mum did.”
Better be safe than sorry. There’s no room for “I think”. It is for the safety and health of your pet, and to avoid your time and money wasted on inaccurate blood tests. For this, postponing the procedure or test is the best option.
“Coco vomited some yellow liquid, should I worry?”
It is basically bile (yellowish or greenish). In some cats and dogs, vomiting bile can happen from long hours of fasting. If your pet is otherwise well, don’t worry. Keep calm and let your veterinary team know when admitting your pet for the procedure/blood test.
“I just gave a teeny-tiny bit of treat to Blackie just now.”
Especially for anaesthesia and sedation, in severe aspiration pneumonia, just a tiny amount of treat can still cost your pet’s life.
For blood tests, it may still be okay. Let your veterinarian know and he/she will advise accordingly.
What happens if fasting my pet did not go as planned?
Be honest
Better be safe than sorry.
Usually being honest isn’t a problem. But occasionally we do have a case or two when clients are ‘unsure’ and want to still go ahead with the procedure as this is the only day they are available in the whole month.
Postpone
Sometimes it can still be done on the same day, just at a later time! Check with your veterinary team, they’ll be happy to help!