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Critical care rabbit anaesthesia

Maximising anaesthesia efficiency is an essential component to achieving a successful outcome in rabbits

01 October 2020, at 8:05am

In practice it is almost guaranteed that at some point a rabbit patient will present, with 900,000 rabbits being estimated as pets in the UK by the PDSA (2019). Whilst the ideal consult would be for routine treatments such as vaccinations, ecto-/endoparasite treatment and health check-ups, the sad reality is, as with all patients within our care, at some point they may require emergency treatment in some capacity.

One of the most common hospital admissions is for gut stasis treatment. It is always important to note that gut stasis is effectively a side effect of a causative condition, rather than being a diagnosis in itself. Whilst it is true that stress (such as changes to environment) and fear can result in ileus, these are often seen to resolve relatively quickly and, in comparison, most gut stasis is caused by some other underlying disease. Four of the more common conditions seen in practice by the author are ear disease, dental disease, liver lobe torsions and gastrointestinal obstruction. Depending on severity, all four will likely require anaesthesia at some point and the status of the patient by this stage can be critical, especially within the latter two conditions.

Assessment and diagnosis of these are varied, with radiography, CT and blood work being used routinely within practice. However, a key indication of the status of a patient with obstruction is the use of blood glucose. A comparatively unobtrusive technique, the utilisation of blood glucose levels gives an instant indication of the patient’s status of blockage (Girling, 2013). With an average of 8.5mmol/l seen within normal rabbit patients, the following blood glucose ranges devised by Harcourt- Brown and Harcourt-Brown (2012) are used to indicate a rabbit’s status and when utilised with other clinical findings, helps devise if surgery and therefore critical anaesthesia is necessary.

  • 9 to 15mmol/l indicates likely GI stasis in some form
  • 15 to 20mmol/l indicates likely partial or progressive obstruction
  • Higher than 20mmol/l indicates a critical patient, almost certainly requiring surgery to remove the blockage and who is going into hypoglycaemic shock

Once the decision has been made to anaesthetise the patient, things will need to progress quickly. The ideal would be to stabilise the patient as much as possible prior to anaesthesia; however, this may be limited if the reason for surgery is time sensitive. Regardless of the cause, fluid therapy should be provided, ideally through a mixture of intravenous and subcutaneous provision. Rabbit maintenance rates are 100ml/kg/24 hours (Grint, 2006) which should be used as a baseline. The assessment of dehydration status is key, and uses an estimated 10ml/kg fluid replacement per 1 percent dehydration. This 10ml/kg is also relevant to 1 percent increase in PCV if bloods have been taken, with a rabbit’s normal PCV range between 0.36 and 0.48 (Flecknell, 1996).

Subcutaneous fluid provision can be provided dorsally between the shoulder blades or in the lateral thorax areas, with a maximum of 30 to 60ml split into a minimum of two sites. Intravenous fluid provision will be limited on the size and stability of the cannula and placement is best achieved within the lateral ear vein, the cephalic vein or the saphenous vein.

Categorising the patient within the American Society of Anaesthesiologists (ASA) classification is important within such critical scenarios and likely the patient will usually be classified as at least a 3. The emergency drugs should be calculated prior to anaesthesia and if the patient is deemed at high risk then the first dosage drugs should be drawn up ready for use (Flecknell and Meredith, 2006):

  • Adrenaline: 0.01mg/kg low dose and 0.1mg/kg high dose
  • Atropine: 0.02mg/kg
  • Glycopyrrolate: 0.02mg/kg

Around 60 percent of rabbits have a serum enzyme called atropinesterase which breaks down atropine, effectively preventing it from working (Flecknell, 2000). As such, glycopyrrolate is a suitable alternative. Atropine has a short-term but instantaneous effect, whilst glycopyrrolate has a delayed onset of action, but a longer lasting effect.

Once intravenous access has been obtained, then suitable analgesia can also be provided; most often this is buprenor-phine at 0.03 to 0.05mg/kg (Harcourt-Brown, 2011). Meloxi-cam should only be used post-operatively and ideally only once the patient’s renal and liver values have been shown to be normal within blood work, as the risk of hypovolaemia in rabbits is high intraoperatively (Girling, 2013). Analgesia will assist in stabilising the patient prior to full anaesthesia as well as reducing the minimum alveolar concentration (MAC) of the anaesthetic gas used during the anaesthesia, in turn reducing the anaesthetic risk. The two most common gaseous agents used in practice will likely be isoflurane or sevoflurane. Each has their own advantages and disadvan-tages; however, the latter is preferred for chamber induction as it is less irritant and the author has found sevoflurane to produce a more stable anaesthetic when the patient is intubated. Anaesthetic induction will ideally be performed via intravenous drugs for greater control, with the author’s prac-tice most commonly utilising alfaxalone at 3 to 4mg/kg via slow provision to prevent apnoea (Grint et al., 2008). Propofol is a common alternative in practice to alfaxalone and, whilst risks of apnoea are higher with its use, can be provided at 5 to 10mg/kg for induction (Girling, 2013). Pre-oxygenation prior to induction is always preferred, ideally two to five min-utes, due to many pet rabbits having underlying respiratory conditions and as such this provision of oxygen will delay desaturation during intubation (Girling, 2013).

Intubated rabbit
FIGURE (1) Patients should be intubated following induction

© Ashton Hollwarth

Once induction has been achieved then the patient should be intubated (Figure 1). Many first opinion practices utilise masks for maintenance of anaesthesia; however, these cannot allow provision of IPPV if required unless the mask is very tightly fitting. In turn, apnoea is very common within rabbits and having the ability to bypass the olfactory components of the respiratory mucosa greatly minimises apnoea and associated complications. As such, the use of endotracheal tubes or v-gel are preferred. In the authors practice, intubation is achieved via endoscopy; however, in first opinion this may not always be possible. Though more technically challenging than in dogs or cats, intubation can be achieved via the eye or laryngoscope. A comparatively recent development of the v-gel laryngeal mask can be used as an alternative for ease. The v-gel sits on the glottis and the lumen, and lies over the larynx to provide inhalation anaesthesia. Though fairly easy to place, they in turn can be easy to “slip” from position during movement in surgery and so placement must always be monitored with capnography.

Intraoperative monitoring of heart rate is best achieved via an oesophageal stethoscope and an expected heart rate under anaesthesia will be around 200 beats per minute or over (Girling, 2013). The use of an oesophageal stethoscope also allows much more clarity to assess heartbeat rhythm, especially within the potentially noisy and limited space of the operating theatre, and as such any issues can be picked up quicker. Respiration rate of 40 to 50 breaths per minute can be expected when conscious so a reduction of this by more than 50 percent under anaesthesia can indicate cause for concern (Harcourt-Brown, 2011). The use of a multiparameter machine provides a much greater range of monitoring. The aim for oxygen saturation is 100 percent whilst anything under 93 percent will indicate significant hypoxaemia requiring IPPV to treat. Capnography allows monitoring of CO2 levels, with acceptable levels being in the range of 35 to 45mmHg (Girling, 2013). Anything above this shows hypercapnia alongside some form of apnoea and, if untreated, cell damage and further reduction in oxygenation will occur. Sudden decreases can indicate a range of issues from machine malfunction to airway obstruction or even a prior warning of cardiac arrest. If IPPV is required, the use of a ventilator allows suitable levels of IPPV to be manually controlled whilst monitoring the patient’s vitals more effectively if available. Alternatively, manual provision can be used; however, this is much harder to achieve effectively longer term whilst monitoring the patient at suitable levels for its risk status (Longley, 2009).

One of the most common risks during anaesthesia in rab-bits is hypothermia, and constant monitoring is required to ensure a normal temperature of 37 to 39.5°C is maintained (Harcourt-Brown, 2011). During anaesthesia you are effec-tively fighting a battle with the effects of the drugs used and techniques required for surgery, namely: peripheral vaso-dilation, the depression of the hypothalamus “thermostat” in the brain and the clipping of hair over the surgical site (Girling, 2013). Maintaining a consistent body temperature is integral for suitable metabolism of drugs as MAC values are reduced if temperature drops too low.

Unfortunately, rabbits are eight times more likely than dogs and six times more likely than cats to have a mortality event under anaesthesia (Brodbelt, 2009). These statistics highlight that maximising anaesthesia efficiency is an essential component of a successful outcome. Post-anaesthesia, rabbits require monitoring, especially in critical cases, as 1 in 72 cases will die within 48 hours of anaesthesia. Post-operative care is just as integral to all of your hard work during a critical anaesthesia, so close patient monitoring should not be ceased once the anaesthetic has ceased.

References
Author Year Title
Brodbelt, D. 2009 Perioperative mortality in small animal anaesthesia. The Veterinary Journal, 182, 152-161
Flecknell, P. 1996 Anaesthesia and analgesia for rodents and rabbits. In: Laber-Laird, K., Swindle, M. and Flecknell, P. (eds) Handbook of Rodent and Rabbit Medicine. 219-237. Pergamon, Oxford
Flecknell, P. 2000 BSAVA's Manual of Rabbit Medicine and Surgery. Gloucester: British Small Animal Veterinary Association
Flecknell, P. and Meredith, A. 2006 BSAVA Manual of rabbit medicine and surgery. 2nd ed. Gloucester: British Small Animal Veterinary Association
Girling, S.J. 2013 Veterinary Nursing of Exotic Pets. 2nd ed. United Kingdom: Wiley-Blackwell
Grint, N. 2006 Analgesia. In: Flecknell, P. and Meredith, A. (eds) BSAVA Manual of rabbit medicine and surgery. 2nd ed. Gloucester: British Small Animal Veterinary Association
Grint, N., Smith, H. and Senior, J. 2008 Clinical evaluation of alfaxalone in cyclodextrin for the induction of anaesthesia in rabbits. Veterinary Record, 163, 395-396
Harcourt-Brown, F. 2011 Critical and emergency care of rabbits. Veterinary Nursing Journal, 26, 443-456
Harcourt-Brown, F. and Harcourt-Brown, S. 2012 Clinical value of blood glucose measurement in pet rabbits. Veterinary Record, 170, 674-674
Longley, L. 2009 Risky rabbits: safe protocols and successful anaesthetic recovery. Vet Times, 39
PDSA 2019 The PDSA Animal Wellbeing (PAW) Report

Adam Gregory, Bsc (Hons), CertHE, DMZAA, RVN, DipVNZS, APVN (Zoo, Wildlife, Small Mammal, Avian, Reptile and Amphibian), has attained experience globally as both a zoo keeper and a veterinary nurse, leading to combine the two areas into his current role. He has developed a particular interest in anaesthesia of non-domestic species and is pursuing this within a certificate of anaesthesia in the near future.

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