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| Hero: "Clearly you forgot to feed me so I will hang out in your gym gear til you remember." |
What’s the hardest thing about taking your pet to the
vet? When I talk to clients, they report that - after trying to get the cat
into a cat carrier - its fasting.
When dogs or cats undergo a procedure, one of the
recommendations is pre-operative fasting. Easier said than done. This is one of
the more challenging aspects of treatment of the animals I live with, because
they’re not stupid. They know the routine and when breakfast isn’t laid out,
they alert me. Repeatedly. Desperately. And unceasingly.
I try all kinds of stunts, for example pretending to
sleep in. They know. I adjust my routine to pretend its earlier than it looks.
They know.
Humans I know who have undergone procedures under
anaesthetic have been almost equally vocal in recounting the inconvenience and
challenge of fasting, especially when paired with some sort of laxative preparation
(fortunately, animals don’t generally need these).
The reasons we fast animals prior to anaesthetic are to
reduce the risk of regurgitation, reduce the risk of aspiration (and aspiration
pneumonia), and sometimes because we want an empty gut to work with (for abdominal
procedures). It can be hard to tell if they experience post-operative nausea,
though some animals clearly do. There are some situations where we don’t have
the option to fast – emergency procedures like passing a urinary catheter in a
cat with an obstruction, for example.
The American Animal Hospital Association recommends a
four hour fast for patients age 6-16 weeks to minimise the risk of
post-operative hypoglycaemia. However, for animals over 16 weeks, “overnight”
fasting is recommended “for procedures scheduled earlier in the day”. But what
counts as overnight? Is dinner the night before allowed? A midnight snack? And
what is “earlier in the day”? I’m a morning person so I’d say before 9am,
though I have colleagues who’d define morning loosely as something that happens
between 10am and 2pm. I suspect the AAHA guidelines are shooting for somewhere
in the middle.
One study found no difference in blood glucose, recovery,
blood gas or cardiorespiratory parameters in cats anaesthetised with
tiletamine-zolazepam fasted for 8, 12 or 18 hours respectively.
In its 2016 Guidelines, the Association of Shelter Veterinarians
states that fasting animals over 16 weeks of age for more than 6 hours is
unnecessary.
This recommendation appears to be based on a study which
found that dogs fed tinned food at half their normal ration three hours before
an anaesthetic did not have significantly increased gastric content and might
have a reduced incidence of gastro-oesophageal reflux.
It would be helpful to look into the risks of benefits of
fasting periods in dogs and cats further so that we can determine optimal
fasting times while maximising patient comfort and welfare.
