Anaesthetic risks study and post anaesthetic gastrointestinal complications following anaesthesia in the European rabbit (Oryctolagus cuniculus): Influence of opioids on gastrointestinal motility

Rabbit (Oryctolagus cuniculus) anaesthesia is considered to be a rather challenging procedure by most veterinarians and this is reflected by the reported higher anaesthetic mortality in rabbits (1.39 %) compared to dogs (0.17 %) and cats (0.24 %). Obviously, rabbits have specific anatomic and physiologic characteristics and should not be considered like companion animals. Rabbits tend to hide symptoms in front of observers despite their domestication around 1500 years ago. Any sign of disease can remain unnoticed by the owner and a veterinarian that is unfamiliar with rabbit medicine. The masking of signs of illness by rabbits continues until the disease enters a far developed stage, making treatment more difficult and anaesthesia, if needed, more dangerous. Rabbits are hindgut fermenter herbivores at huge risks of decrease in gastrointestinal function that quickly leads to enterotoxaemia which can be fatal because of gas accumulation, distension of digestive organs and bacterial translocation.
The first aim of this thesis was to evaluate, within the context of a Teaching Veterinary Institution, the actual mortality related to anaesthesia in rabbits. Data were collected from 2013 to 2018 and 112 cases were retrospectively assessed. Results of this study revealed that mortality was higher in healthy individuals and in case of diseased rabbits in the Exotic Pet Animal Hospital versus existing data in the literature, respectively. Gastrointestinal complications following a desexing surgery were also studied. Fifty percent of rabbits neutered experienced gastrointestinal issues following the surgery. The adjunction of metoclopramide, a putative prokinetic drug in the rabbit, as a postoperative medication to prevent gastrointestinal issues, was not found beneficial.
Potential gastrointestinal side effects of anaesthetic molecules have been studied and some decrease in gastrointestinal function consequences have been suspected on the rabbit digestive tract. On the other hand, opioids are well known in human medicine for constipation outcomes and these results have often been transposed to the rabbit, without any scientific proof to date. Consequently, the second aim of this thesis was to investigate the potential side effect of the opioid used in desexing surgeries’ anaesthetic protocols in the Exotic Pet Animal Hospital of the University of Liege, namely buprenorphine, to evaluate its impact on gastrointestinal transit in the postoperative period of rabbit patients. For this purpose, a non-invasive imaging protocol was designed to evaluate the gastrointestinal transit of rabbits by means of ultrasound pyloric and duodenal contraction counting and barium follow through radiographs. It appeared that after a single high administration of buprenorphine, gastrointestinal transit of rabbits is not decreased in function and the alimentary bolus continues its physiological progression.
The third aim of this thesis was to apply this new non-invasive imaging protocol to other opioid molecules currently used in rabbit medicine, such as morphine, butorphanol and tramadol. Results of this study indicated that a single high dose of butorphanol or morphine temporarily slowed gastrointestinal transit in healthy rabbits, preventing physiological progression of the alimentary bolus without the induction of ileus. In contrast, a single dose of tramadol did not seem to lead to noticeable gastrointestinal transit decrease in function. After 24 hours follow up, the rabbits’ transit returned to their baseline values.