Alfaxan® Multidose in Pet Rabbits

Alfaxan® Multidose is now licensed for induction of anaesthesia in pet rabbits.

Rabbits are the 3rd most commonly anaesthetised pet in the United Kingdom⁷⁰ and to achieve best practice outcomes it is vital to understand the unique physiology, behaviour and anaesthetic requirements of rabbits.

The CEPSAF study⁷⁰showed that rabbits had 7 times greater overall greater risk of anaesthetic death than dogs, so it is clear there must be some differences that need consideration before anaesthetising rabbits.

Behaviour

Rabbits are prey animals so if confronted with the scent, sight or sound of a predator, such as dogs and cats, stress responses will be initiated – even if the rabbit is well handled and healthy. Stress results in changes in physiology through increased circulating cortisol and catecholamines, which is not ideal when anaesthetising any patient.

Physiology

The uniqueness of rabbit physiology means they need to be managed differently to dogs and cats. For example, rabbits should not be fasted prior to anaesthesia, as this will put them at risk of hypoglycaemia and gastrointestinal stasis. Other physiologic differences exhibited by rabbits that should be considered are outlined in Table A.

Table A: Some key physiological differences between rabbits and other species
Consideration	Impact on anaesthetic procedures
Prey species	More likely to exhibit a stress response with high ciruclating cortisol and catecholamins
Hind gut digester	Requires continual movement of food through gut to maintain normo-glycaemia and intestinal motility
Circulating Atropinase	Rapid breakdown and therefore lack of effect from atropine administration

Anatomy

There are multiple anatomical differences that need to be considered when anaesthetising rabbits. One obvious difference is that they are obligate nose breathers, and as a result can be more difficult to intubate than the average dog or cat. Other anatomical differences that can impact on anaesthetic risk are outlined in Table B.

Table B: Some key anatomical differences between rabbits and other species
Consideration	Impact on anaesthetic procedures
Obligate nose breather	Can be slightly more challenging to intubate and upper respiratory disease can cause serious health issues
Small lung capacity	Caution is required when mechanically ventilating and any excessive deadspace can compromise the patient
Continual teeth growth	Moderate oral cavity disease can lead to serious health issues and make intubation more difficult
Intestinal fill effect	Impedance to normal ventilation from gut fill means rabbits often benefit from slightly raised head position, especially when in dorsal recumbency

Pre-Anaesthetic checks

Ensure the rabbit has food and water until being placed in their carrier and preferably whilst in the carrier as well
If they have a bonded companion, recommend they are presented together to the clinic
The owner has brought enough food from home to feed the rabbit/s during the stay
At admission, rabbits should avoid waiting in reception areas with dogs and cats.

A minimal time between admission and anaesthesia is preferred for rabbits (the longer a rabbit is in a strange environment surrounded by the scent, sight and sounds of predators the more stressed it will become).

Recommended evaluations that should occur pre-anaesthesia.

Parameter	Assessment
Body Condition Score	Ensure that patients are weighed and an appropriate condition score is applied. Overweight rabbits may benefit from delaying elective procedures to allow weight loss
Cardiovascular System	Pink Mucous Membranes with good refill Heart rate (135 to 325 bpm) Regular rhythm
Respiratory Rate	Regular rythm, not laboured, clear on auscultation Respiratory Rate (40 to 60 bpm]
Body Temperature	38.5 – 40℃
Basic Laboratory Parameters	PCV – 33 to 45% TP – 5.4 to 7.3 g/dL Blood Glucose – 80 to 150 mg/dL

Alfaxan^® Multidose and Anaesthetic Induction of Rabbits

Numerous published peer-reviewed papers have investigated Alfaxan as an anaesthetic induction agent for rabbits. ^{12, 13, 14} Controlled intravenous administration of Alfaxan offers a wide safety margin and an excellent cardio-respiratory profile, making it an excellent choice for anaesthetic induction of rabbits. Alfaxan produces

good muscle relaxation,
smooth transition from conscious to anaesthetised,
good conditions for endotracheal intubation,
the ability to titrate the dose to required anaesthetic depth,
the ability to top-up if required and
rapid clearance and recovery.

When first learning to use Alfaxan Multidose in pet rabbits, draw up the recommended dose of 2mg/kg and administer by slow intravenous injection until the patient is fully anaesthetised then manage the airway using appropriate techniques.

An intravenous cannula should be used to aid controlled delivery of Alfaxan Multidose (see Diagram A for a suggested location in the marginal ear vein). Administer 1/4 of the drawn-up dose every 20-25 seconds flushing the cannula between increments.

Please see the Alfaxan Multidose Pet Rabbit User Guide for more details

Diagram A showing the location of the main ear veins in the rabbit and cannula placement.

Intubation

Rabbits are obligate nose breathers. As a result, any food in the mouth can be gently flushed out with water prior to attempting intubation, with little risk of aspiration.

Positioning a rabbit to allow dislocation of the soft palate and allow visualisation of the larynx is shown in Diagram B

Use of local anaesthetic administration to the larynx may allow for easier intubation and decreased risk of laryngospasm, however it is important to remember that local anaesthetic does not take effect instantaneously. Visualising the larynx when placing an endotracheal tube can be aided by use of a laryngoscope, otoscope or endoscope.

An alternative to intubation is the use of a laryngeal mask device. Correct placement of these devices requires some training. It is highly recommended when securing airways that you confirm placement using a capnograph (end tidal CO₂ monitor).

Diagram B: Showing optimal positioning of the rabbit to allow dislocation of the soft palate and visualisation of the larynx.

Maintenance

Anaesthesia can be maintained with isoflurane or sevoflurane.

It is important to consider:

The small respiratory tidal volume necessitates minimal dead space
Minimal excursions will be seen in the rebreathing bag
Heart rate changes little in response to changes in anaesthetic depth so breathing rate and pattern are more useful indicators of this

Gastrointestinal fill can add pressure to the diaphragm and interfere with ventilation, so slight elevation of the thorax is recommended.

Recovery

The recovery area should be warm, well separated from dogs and cats and have the crash and re-intubation equipment on hand.

Alfaxan is rapidly cleared by rabbits, however the effects of other drugs like medetomidine may still have significant effects in the recovery period. Judicious use of reversal agents such as atipamezole can be considered. Extubation of the patient can be performed when they exhibit increased jaw tone and tongue movements. Pain relief is recommended where appropriate.

Early re-introduction to a companion and early re-introduction of fluids and feeding are considered very important for minimising stress and maintaining healthy gastrointestinal function.

Resources

Visit our resources section for additional information and tools for your clinic.