Rabbit Anaesthesia
Unless you are anaesthetising rabbits regularly, seeing a rabbit dental or ovariohysterectomy on your surgery list for the day may cause a restless night’s sleep. Added to this the pressure of working with a celebrity client (the Easter Bunny) creates another level anxiety. However being unfamiliar with the species is only part of what makes performing rabbit anaesthesia difficult. They are small, difficult to intubate and gain venous access. The anaesthetic protocols differ vastly from our more commonly anaesthetised dogs and cats. And there is limited literature describing anaesthesia and analgesia for domesticated (non-experimental) rabbits. Coupled with this rabbits often present for anaesthesia with subclinical respiratory disease. Brodbelt et al in 2008 identified that 1 in 72 rabbits died secondary to anaesthesia. This was compared to 1 in 600 dogs, or 1 in 419 cats. Although this number has improved significantly since 1990 (Clarke and Hall reported that 1 in 28 rabbits died secondary to anaesthesia), there is room for improvement.
So what can we do to improve our rabbit anaesthesia?
As with any anaesthetic prior planning and preparation, where possible, is the key. Pre-operative stabilisation should be performed where possible. This may be via dietary or fluid therapy supplementation, or treatment of underlying respiratory disease.
A premedication agent should be considered as rabbits can become easily stressed with handling. Stress and struggling may result in vertebral fractures and predispose the rabbit to catecholamine-induced arrhythmias. Intravenous access allows for administration of fluids, the ability to titrate induction agents to effect and also to administer emergency drugs. Application of a local anaesthetic cream such as EMLA can improve patient compliance, however needs to be applied 30-40 mins prior to catheter placement. A 22 or 24 gauge catheter is usually appropriate for catheterisation of the marginal ear vein.
Prior to induction pre-oxygenation should also be considered. Pet rabbits often have subclinical respiratory disease and administering oxygen via face mask or chamber may minimise hypoxia at induction. Induction can be via intravenous, intramuscular or inhalational routes. However if using inhalational induction the author recommends that the animal is well sedated beforehand.
Endotracheal intubation is recommended for rabbits for all but the shortest of procedures. The larynx of the rabbit can be visualised using a rigid scope or otoscope. This allows for insertion of a soft stylet into the airway, which can be used to guide the ET tube into the correct location. Alternatively blind intubation may also be performed. More recently rabbit specific laryngeal mask airways have been developed which allow for easy, rapid airway management and ventilation where required. Capnography is also a valuable tool to confirm endotracheal intubation in rabbits or any other species with a difficult airway.
Inhalational anaesthesia should be maintained using a low resistance, non rebreathing system such as an Ayres T piece. Monitoringcan be performed using pulse oximetry, capnography and ECG. Doppler is best for measuring blood pressure as most oscillometric systems are not validated for rabbits.
Pre-emptive analgesia should always be considered. This may include opioids, non steroidal anti-inflammatories and local techniques. Care should be taken when using local techniques in rabbits not to exceed the toxic dose. Retrobulbar block is also contra-indicated in rabbits as vascular injection is likely.
Thermoregulation and maintenance of body temperature under anaesthesia is important. Hypothermia will contribute to a protracted recovery.
Recovery should be closely monitored. The majority of anaesthetic deaths occur in this period. Particular attention should be paid the airway and ventilation. Rabbits should be kept warm, pain free and away from predators and noise. Food should be offered as soon as the patient is sufficiently recovered in order to reduce the incidence of ileus.
Rabbit anaesthesia consultancy and education sessions are another service offered by Veterinary Anaesthesia Specialists. Above and to the right are pictures of “Dudley” who was recently anaesthetised for cataract surgery for Melbourne EyeVet. He is now home with his owner and looking forward to Easter.
Happy Easter from Leah @ Veterinary Anaesthesia Specialists
