It is a standard protocol to withhold food from patients before they undergo a sedation or an anaesthetic for a period of time – both in the veterinary and human field. However, over the past few years the number of hours your pet needs to be ‘nil by mouth’ before surgery has sparked many debates and there is variability between fasting recommendations. This article will extract and discuss these debates through the area of evidence based Veterinary medicine.

Why do we starve pets before surgery?

When your beloved pet is booked in to have a surgical procedure the following day, the anaesthetic protocol starts with you at home, by following the fasting instructions! 

The overall goal with fasting patients is to reduce the volume of stomach contents to prevent gastroesophageal reflux (GER) (regurgitation of stomach contents) and aspiration (inhalation of stomach contents) (Robertson, 2018). Preventing inhalation of stomach contents whilst under anaesthesia is vitally important. If stomach contents are inhaled under anaesthesia, this can lead to pneumonia and even sometimes death. 

Fasting recommendations 

Now this is when things can become a little bit more complicated. Unfortunately, fasting recommendations are not always textbook. Timings can be influenced by many variable factors including patient age, weight and other health issues such as diabetes. For instance, in very young puppies and kittens, it is recommended to withhold food for no longer than 1-2 hours before surgery. 

Previously, many recommendations suggested starving your healthy dog or cat for approximately 12 hours before surgery. A common practice protocol is to advise that owner’s starve their dog or cat from midnight. This generally leads to a 12 hour starvation period (or sometimes longer depending on the theatre list and when they’re actually going to be in theatre) before their surgical procedure. However, there is little evidence based medicine to support this guideline. Practically, this guideline is relatively easy for owners to adhere to. Most pets will be fed their normal evening meal and then will remain ‘nil by mouth’ after this. 

Newer research is challenging this

More recent guidelines and emerging evidence suggests that food should only be withheld 4-6 hours before surgery (Grubb, 2020). This is also supported by studies investigating reflux and how the duration of fasting can affect this. Saavas (2016) performed a study looking at the effect of feeding dogs a ‘light meal’ 3 hours before surgery on the incidence of reflux. They discovered that feeding a small meal 3 hours before surgery reduced the risk. However, conflicting this, an alternative study concluded that feeding a light meal 3 hours before surgery was associated with greater odds of reflux and regurgitation, compared with overnight food withholding (Viskjer and Sjostrom, 2017).

There are certain breeds of dog which are more prone to regurgitation. Consequently practices may alter their anaesthetic protocols to the increased risk of aspiration under anaesthesia. Brachycephalic dogs (and cats too!) pose an increased risk during and after anaesthesia. This is due to their conformation and respiratory problems (Downing and Gibson, 2018). Popular at risk breeds include Bulldogs, French bulldogs and Pugs (this list is not exclusive!). Grubb (2020) therefore recommends that these animals are fasted for a longer period of 6-12 hours before surgery to lower this risk.

Your veterinary practice will always instruct you on their recommended fasting times before surgery – because as we’ve seen it’s really complicated, so we try to choose the right period for your pet as an individual

Do I need to withhold water?

Again, there is a slight variability between water withholding protocols. Mostresearch now suggests that in healthy and young patients, water does not need to be withheld prior to surgery (Grubb, 2020). Robertson (2018) states that water should be available to patients until the time of premedication. Some practices do still advise removing water from patients 1-2 hours before the time of surgery. Furthermore, it is recommended that dogs who are at a higher risk of regurgitation or have a known history of regurgitation have their water withheld for 6-12 hours (Grubb, 2020).

Your veterinary practice will always instruct you on whether you need to withhold water from your pet. 

Does the same fasting recommendations apply to all species?

No! There is species variability between fasting guidelines pre-surgery. In comparison to dogs and cats, rabbits should never be starved before anaesthesia! Since University, I have always imagined rabbits as being like ‘miniature horses’ with respect to their gastrointestinal tract! It is important to encourage rabbits to eat as much as possible right until their surgery, to keep their gastrointestinal tract moving and to try to prevent gut stasis.

Your Veterinary practice will guide you on fasting instructions for other species.


There is definitely food for thought here, excuse the pun! Although interestingly, there are discrepancies amongst the literature with regards to the ideal fasting duration pre-surgery, the overall modern consensus appears that the fasting duration leading up to surgery has decreased (Grubb et al, 2020). With new evidence emerging within both the Veterinary and human field, watch this space!


Downing, F. Gibson, S. 2018. Anaesthesia of brachycephalic dogs. Journal of small animal practice. 59. 725-733.

Grubb, T. Sager, J. Gaynor, J. Montgomery, E. Parker, J. Shafford, H. Tearney, C. 2020. 2020 AAHA anaesthesia monitoring guidelines for dogs and cats.

Robertson, S, A. Gogolski, S, M. Pascoe, P. Shafford, H, L. Grigginhagen, G, M. 2018. Feline anaesthesia guidelines. Journal of feline medicine and surgery. 20: 602-634.

Savvas, I. Raptopoulis, D. Rallis, T. 2016. A ‘light meal’ three hours perioperatively decreases the incidence of gastro-oeseophageal reflux in dogs. Journal of Animal Hospital Association. 357- 363.

Viskier, S. Sjostrom, L. 2017.Effect of the duration of food with holding prior to anaesthesia on gastrooesophageal reflux and regurgitation in healthy dogs undergoing elective orthopaedic surgery. J Vet Rest. 144-150.

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