It also will help prevent the dreaded un-bonding phenomenon which sometimes occurs when one member of a bonded pair comes home smelling of strange and scary hospital. Unfortunately, this goes for bonded groups, too. Its best to bring everyone in for moral support and to prevent post-operative social rejection. Some surgical anesthetics can cause nausea. One of the reasons vets fast most animals pre-operatively is because of the risk of vomiting during surgery or recovery.
Rabbits lack the vomiting reflex, and are physically almost incapable of regurgitation.
There are two reasons that this should not be a concern with rabbits. Under normal circumstances, the intestine of a healthy rabbit is never empty, and should not be. Also, since an anorectic rabbit can begin to suffer liver damage in relatively short time when the gut is empty, it is not advisable to fast the rabbit before surgery. If the veterinarian is using isoflurane or sevoflurane, the gas anesthetic of choice, body weight is not an issue, since the gas is adminstered through the respiratory tract. Even though isoflurane gas is more expensive than injectible anesthetics, it is worth the extra cost to ensure a safer surgery and faster recovery.