Introduction to Rabbit Anaesthesia
Abstract
This article provides an introduction to rabbit anaesthesia particularly aimed at student veterinary nurses. Throughout the years, many people have found rabbits to be a daunting experience, one which carries many fears throughout practice. This is due to the high mortality rate in comparison to other companion animals such as cats and dogs. This article will provide vital information, tips and tricks on rabbit anaesthesia for those starting out in their nursing journey.
Introduction
It does not matter how long a veterinary nurse has been qualified, it is still common to hear their worries when they are about to prepare for a procedure involving a rabbit anaesthesia. With rabbits being the third popular companion animal [1], it is vital that veterinary nurses have an understanding of rabbit care and how to prepare for their surgical procedure, monitoring of anaesthesia and recovery.
Learning outcomes
· Have an understanding of pre-operative care of rabbits anaesthesia
· Physiological effects of pre-medications
· Basic monitoring of anaesthesia
· Recovering rabbits from their procedure
Pre-anaesthetic care
Performing a clinical exam of the rabbit is crucial in providing baseline parameters. Baseline parameters include recording their heart rate and rhythm, respiratory rate, mucous membrane colour, capillary refill time, temperature, weight, and if possible, their blood pressure. Although it can be useful to compare against species specific data, it is more ideal to compare it against the individuals baseline parameters [2]. The effects of stress can affect the baseline parameters so it is a good idea to place the rabbit in a darkened, quiet room prior to handling. When gathering the baseline parameters, measure the respiratory rate prior to handling. Causes of stress include, but are not limited to, being within a new environment, handling, travelling, unfamiliar people and being in close proximity to predators.
When assigning rabbits to an anaesthetic risk group, it is important to remember that although they are higher risk patients for anaesthesia, they should still be assigned correctly rather than placing them into a higher risk group due to the species. The American Society of Anaesthesiologists (ASA) physical status scale is commonly used in practice and can help with assigning the patient to the correct group (Table 1) [3].
Unlike cats and dogs, rabbits must not have food withheld for a long period of time prior to their procedure due to rabbits not having the ability to vomit, and, if starved, this can lead to ileus. Rabbits should only be fasted for a maximum time of one hour prior to anaesthesia. This is to ensure there is no, or at least minimal, food in their mouth prior to intubation and to ensure their airways are entirely clear [4].
Once the patient has settled, it is best to prepare them with an intravenous catheter which is usually placed in the marginal ear vein [5]. If required, it can also be placed into the cephalic or saphenous vein but, more commonly, the marginal ear vein is used and it is less stressful for the rabbit.
Pre-medications and physiological effects
Pre-medications are used to calm the patient, provide pre-emptive analgesia, encourage a smoother induction of anaesthesia and recovery and reduce the dose of maintenance drugs [6]. A triple combination of medetomidine, ketamine and butorphanol is commonly used in practice as a pre-medication in rabbits – medetomidine being the sedation, ketamine being the anaesthesia, and butorphanol being the analgesia. It is important to allow 10-15 minutes for the pre-medication to effect as it helps to reduce the amount of induction agent required. Once the rabbit has been pre-medicated, it is vital for them to pre-oxygenated with a mask.
Physiologic effects of pre-medication drugs can be seen in table 2 [7].
Airway management
Some practices will use a mask for airway management but if a rabbit can be intubated, this is best practice. The rabbit should be positioned in sternal with its head in a vertical position. Once intubated, capnography should be used to ensure accurate ventilation and this should be measuring between 35-45mmHg. If it is not possible to intubate, then a mask can be used but it must be tight fitting around their mouth and cotton wool should be wedged around the mask to prevent inhalational gas leakage [8].
Monitoring anaesthesia
The temperature of rabbits should ideally be maintained between 38.5-40 degrees Celsius. This can be achieved by ensuring room temperature is warm, warm air blankets, socks and wrapping the patient in bubble wrap [9]. Other options also include the use of hot water bottles, microwavable heat packs and warm water filled surgical gloves although constant monitoring and caution must be taken when using those options. Rabbits can become hypothermic rapidly but they can also become hyperthermic just as quickly as their sweat glands are not very effective due to their thick fur.
Vitals to be monitored during anaesthesia include temperature, heart rate, respiratory rate, mucous membrane colour and capillary refill time, pulse oximetry, blood pressure and capnograph readings [10]. Although it is useful to have a multiparameter to work alongside, these machines often cannot keep up with the parameters rabbits display. In some rabbit breeds, their heart rate can reach around 300bpm when resting. Multiparameters are not designed to measure heart rates this high so may give a false reading. Normal clinical parameters can be seen in table 3.
Rabbit jaw tone, pedal reflex and eye position cannot be determined when assessing the depth of anaesthesia as rabbit jaw tones tend to remain a little bit taut and their eye position is usually central. Particularly in prey species, testing the pedal reflex does not provide an accurate representation of anaesthesia depth [11].
It is a good idea to get a baseline parameter of the rabbits blood pressure prior to pre-medicating. This can help towards assessing the depth of anaesthesia. If there’s no variation in the blood pressure, it can suggest that the rabbit is stable therefore anaesthesia should be maintained. If there is an increase, it can suggest there’s inadequate anaesthesia and analgesia. If there is a decrease, it can suggest a possible overdose of anaesthesia therefore requiring the inhalational gas to be reduced. A decrease can also indicate blood and fluid loss so any changes in parameters must be communicated to the veterinary surgeon [12].
Consideration for anaesthesia
Some considerations for anaesthesia include remembering that rabbits are nasal breathers therefore it is important to ensure that their nasal passages are not blocked as this can cause them to panic and will increase their stress levels. They also have large abdomens when placing them in sternal recumbency, elevate their chest slightly more than their abdomen to help reduce pressure on their diaphragm. Iatrogenic bloat (filling the stomach with air) can occur if the rabbit is incorrectly intubated via the oesophagus, not the trachea [13]. Their eyes should also be lubricated as they lose their intermittent blink reflex which rehydrates the corneal surface and this will help to prevent corneal ulcers from forming [14].
Recovery
When the procedure has been completed, it is vital that the rabbit is closely monitored. They should be positioned in sternal recumbency with the thorax slightly elevated above the abdomen [15]. Their vitals should be checked every 5-10 minutes (sooner, if required). Pain scoring should also be monitored by using the Newcastle University Rabbit Grimace Scale. As soon as the rabbit is awake and able to swallow, they should be offered food and water as they are prone to developing ileus rapidly. Should the rabbit not be seen eating, it is strongly recommended that the rabbit is syringe fed with a recovery food. This will encourage their gut to continue moving, help with hydration and encourage recovery.
Conclusion
Although the responsibility lies ultimately with the veterinary surgeon in charge of the case, veterinary nurses play a crucial role in caring for rabbit patients and ensuring all steps of anaesthesia are prepared for. Being knowledgeable within this area can be the difference between life or death for the patient. All members of the team should work together, provide support to those who are less knowledgeable in rabbit anaesthesia and all be willing to learn and expand on skills.