Holistic rabbit anaesthesia

The influence of other factors on anaesthesia

Rather than thinking about drug doses as the only factor that affects safety, it is more productive to consider the whole picture.

Bonding

Rabbits are highly social creatures. A lone rabbit in the wild will rapidly get picked off by predators. Without a ‘buddy’ to watch their back, rabbits can never relax and are constantly monitoring for danger, even in familiar environments. Their need for companionship and backup is very significant indeed and is shown by the reduced rate of post-anaesthetic complications in rabbits presented for surgery in a bonded pair so that the rabbit wakes up with its companion close by.

Make sure that you consider the fact that this is a prey species. Keeping rabbits away from predators and giving them hiding places including a towel wrap during examination is useful to produce an unstressed patient (and staff!).

The diet is very important and has a great influence on anaesthetic complications:

The incisor teeth cut grass efficiently while the cheek teeth shred it. The small intestine has very little part to play in the initial digestion of hay and grass. The fusus coli helps to separate digestible from indigestible fibre. Indigestible fibre is

excreted in hard rabbit pellets, while digestible fibre is moved to the caecum.

Caecal fermentation of digestible fibre produces volatile fatty acids (VFAs) amongst other chemicals. VFAs can be absorbed directly across the caecal mucosa or be digested from caecotrophs.

Caecotrophs are packaged and produced from caecal contents and are excreted and immediately eaten. The contents are then digested in the small intestine.

The small intestine has a rapid transit time. Excessive starch in the domestic rabbit diet is dumped into the caecum where it has the effect of changing the caecal flora; leading to serious or fatal disease conditions.

Housing

Rabbits need large amounts of space with outdoor grazing areas and dry, well ventilated indoor areas to reduce disease risk. Standard hutches should only be used as a shelter within a larger enclosure. Converted sheds, playhouses or aviaries are recommended. The RWAF recommendation for the minimum size enclosure is 3m x 2m x 1m high. Attention should be paid to ventilation, weather and predator proofing.

Rabbits need exposure to natural light to reduce the risk of vitamin D deficiency – this must be taken into account, especially for house rabbits. Indoor rabbits will take every opportunity to chew electrical cables – these should be heavily protected or moved out of the way.

Rabbits housed in small, dirty or dusty environments are much more likely to have undiagnosed upper or lower respiratory disease which will have a negative effect on anaesthetic safety.

The domestic rabbit diet should consist of:

• Hay and grass (typically a ball of hay at least the same size as the rabbit per day).

• Mixed leafy green vegetables/herbs in small amounts (1 handful per day, no bigger than the rabbits own head).

• A small volume of an extruded, high crude fibre rabbit pellet food. (Adults need 1 tablespoon of pellets per kg of IDEAL bodyweight per day).

Grass and hay should comprise the majority of the diet which results in a well-balanced caecal microflora. Remember that a healthy caecum will produce heat (from fermentation) and a continuous stream of VFAs into the bloodstream. This is very useful indeed throughout the surgical and recovery periods. Rabbits with a healthy caecum are less likely to experience ileus and even if they do, it will be easier to treat.

Changes should be made slowly over a period of 4-6 weeks before surgery. If this is not possible, diet change should not be started until the rabbit has fully recovered from surgery (at least 2 weeks).

Respiratory anatomy

Rabbits are sprinters, not long distance runners. Their abdominal volume is very large compared to the thoracic volume. The lung fields arch dorsally and caudally over the diaphragm, liver and stomach. This means that when positioned on their back for surgery, the abdominal contents compress much of their lung field. The heart may compress even more lung, leaving the patient with very little functional lung volume. Gently tilting the rabbits (ideally using a surgical bean bag) can slide the abdominal contents caudally and relieve some of this pressure. Ventilation (supplementary IPPV or a simple ventilator) is very useful in most procedures to inflate the lungs. The majority of rabbits struggle to ventilate without assistance under anaesthesia. Long anaesthetics, compression of the thorax in a trough or upper respiratory disease will all compound the problem. Ventilation should be managed to maintain the end tidal CO2 readings between 35 and 45mmHg.

Summary

Correct husbandry and understanding of respiratory and digestive physiology and anatomy will lower the risk of anaesthetic complications.
Attention to detail on these points will improve the success rates of clinical treatment and significantly improve the welfare of patients.


Produced in association with LagoLearn

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