Successfully managing anaesthesia for feline patients requiring oral surgery

Feline patients present regularly for oral surgery, ranging from a simpler scale and polish to surgery to correct trauma caused from road traffic accidents, for example. All oral surgery must be performed under general anaesthesia (GA) to ensure the patient remains immobile and pain free and, importantly, so that we can safely maintain their airway (Gracis and Reiter, 2018). Cats can be more technically challenging under GA for oral surgery, and their management must therefore be carefully considered (Robertson et al., 2018).

This article aims to walk you through the case management of a 12-month-old male neutered feline Bengal who presented to the referral clinic for fixation of a mandibular symphyseal separation following the unfortunate failing of fixation with both cerclage wire and nylon suture.

Background

The patient presented to the emergency clinic having returned home with blood around his face and showing signs of oral discomfort. Analgesia was administered and he was monitored closely for signs of cranial trauma. Once deemed stable, initial skull radiographs and a physical exam revealed a mandibular symphysis separation. Abdominal, pelvic and chest radiographs revealed no abnormalities.

The patient presented to us at the referral centre bright, in particularly good condition, without signs of dehydration. He had received meloxicam SID for 10 days.

Cats presented for oral surgery have commonly been unable to eat or drink normally for a period. As such, they often present underweight and dehydrated with a poor body condition. This leaves the veterinary team in a difficult position. Ideally, we should correct their status prior to the anaesthesia; however, in some cases, this cannot be corrected until the primary complaint is treated.

Whilst we may not be able to correct these concerns, we can improve them, resulting in the patient being in the best physiological state prior to anaesthesia. Initial intravenous fluid therapy (IVFT) is recommended along with testing their electrolytes, with supplementation via IVFT as required (Johnson and Snyder, 2015). We must be careful when setting fluid rates for cats under GA; current recommendations are 3ml/kg/hr to avoid adverse effects (Grubb et al., 2020).

Analgesia and anaesthesia

Patient handling and premedication choices should be adapted for cats presenting with chronic oral pain. It may be wise to administer analgesia prior to placement of an intravenous catheter (IVC) and the use of gabapentin prior to admission can be considered (Gracis and Reiter, 2018). An IVC should be placed in all patients receiving anaesthesia, but a medial saphenous IVC placement may be better tolerated. This is a preferable IVC site, being further away from the bacteria-laden spray created during oral surgery.

After a full physical assessment and consideration of blood results if necessary, all patients should have a tailored premedication plan, comprising both analgesic and sedative properties. Emergency drug dosages should be calculated prior to administration of any drugs for all anaesthesia patients, and the location of such drugs known to all (Duke-Novakovski et al., 2016).

The patient in this case was particularly lively, so a lumbar intramuscular premedication regime was administered, consisting of 5µg/kg medetomidine and 0.2mg/kg methadone.

Medetomidine was chosen for its excellent sedative properties, the ability to antagonise it if required and its analgesic properties. It also causes vasoconstriction which reduces peripheral heat loss. It holds a swift onset, and a small volume can be administered, meaning less pain upon injection (Duke-Novakovski et al., 2016).

Methadone is a pure mu opioid, chosen as it can easily be titrated and provides excellent analgesia for oral surgery. The use of butorphanol for oral surgery is far from ideal as its effects are short lived with pain relief less optimal than other opioids (Gracis and Reiter, 2018).

Patients must be monitored closely once an alpha-2-agonist has been administered. They may vomit putting them at risk of aspiration, and it can also have profound cardiovascular effects if used in high doses. Premedication will only work as well as its environment allows, so keep lights low and noise to a minimum.

Once the patient was appropriately sedated, and an IVC placed, alfaxalone was administered intravenously, slowly and to effect, the total dose administered being 2mg/kg.

Airway maintenance

Cats have a small and delicate airway, and the larynx and trachea can be easily damaged (Robertson et al., 2018). Laryngospasm can occur in cats when the laryngeal tissues are irritated during intubation (Bryant, 2010; Box 1).

Once intubated, the endotracheal tube (ETT) was secured with a plastic tie behind the ears, preventing water tracking up and saturating the patient, and keeping the ETT stable.

A modified Ayre's T-piece breathing circuit was connected to the ETT, using a capnography elbow adaptor to reduce drag. The modified Ayre’s T-piece does not have any valves on the inspiratory limb, thereby reducing resistance on inspiration, so is ideal for use in feline patients. It is also appropriate for intermittent positive pressure ventilation (IPPV) should it become necessary (Welsh, 2009).

Monitoring

The use of modern anaesthesia monitoring devices can be problematic in smaller patients as they can be cumbersome and not offer accurate results. During oral surgery we cannot rely on areas of the face where we may usually apply a monitoring device or check a reflex (de Vries and Putter, 2015). Alternative areas to place the pulse oximeter are the vulva, prepuce, toe web, toes or inguinal area. Regular chest auscultation is also vital to assess the heart and lungs, which can tire during a lengthy anaesthetic, particularly if a patient is kept on one side for a prolonged amount of time. It will also allow you to be aware of any heart murmurs or arrythmias.

Although daunting, an electrocardiogram (ECG) will supply vital information, so aim to use it on all patients. Learn what is normal and alert your veterinarian if an abnormal trace is noted. The use of alpha-2-agonists, even at incredibly low doses, can cause second degree atrioventricular block. If the patient’s blood pressure stays within normal limits, this should not need to be acted upon but closely monitored for any changes. ECGs can be frustrating, with the potential for interference. Ensure ECG pads have appropriate amounts of lubrication, limbs are not touching and no electrical leads are in contact with the ECG line.

Capnography should be used for all anaesthesia. It provides vital information on the patient’s respiratory status and rate, and will alert you to a kinked, blocked or disconnected ETT – all of which are common threats in oral surgery. Aim for an end tidal carbon dioxide (ETCO₂) to remain within 35 to 45mmHg (Welsh, 2009).

Hypotension is a common occurrence under GA. Oscillometric devices will not be as accurate as the doppler in felines, and some studies suggest the doppler reading is nearer to the mean arterial pressure (MAP) in feline patients (Bryant, 2010).

A confirmed MAP below 60mmHg is classed as hypotension and must be acted upon swiftly to avoid detrimental effect to internal organs. The cause of the hypotension should be identified prior to administering treatment. A good first step is to reduce the inspired volatile agent concentration (Robertson et al., 2018). Additional analgesia or sedation may be required to reduce the volatile agent. The application of local anaesthesia nerve blocks is gold standard. Check your blood pressure cuff placement and size. The tail base or hindlimb are excellent choices and the cuff width should be 40 percent of the limb/tail circumference (Welsh, 2009). An IV fluid bolus may be required but be very wary of overloading felines with fluid therapy. Anticholinergics are used to combat hypotension induced by bradycardia. The use of vasopressors can also be considered (Duke-Novakovski et al., 2016). It is also important to note that cats are particularly prone to hypothermia under anaesthesia (Boxes 2 and 3).

The patient remained normothermic throughout. It is imperative to monitor temperature regularly, record it and act on the result (Box 3). It is important to note that hypothermia will reduce anaesthesia drug requirements, mean-ing a chance of accidental overdose as well as delaying recovery and healing, and increasing oxygen requirements (Duke-Novakovski et al., 2016). Although less common, we must not allow our patients to become hyperthermic when using heating aids.

Fixation of the mandibular symphyseal separation by the application of an acrylic splint

This technique has many benefits (Box 4) and can be applied to mandibular or maxillary fractures, the technique of which is outside the remit of this article but has been described in depth in the literature (Gorrel, 2004). The whole mouth must be assessed for further trauma prior to fixation with the use of dental radiography and a head CT as gold standard.

For our patient, a wire splint was placed around 304 and 404, stabilising the separation of the mandibular symphysis. This was covered with an acrylic splint, to remain in place for four weeks (Figure 1).

Recovery

The patient had a smooth recovery, with a rectal temperature of 38.6°C, a MAP of 110mmHg and a heart rate of 160bpm. He ate warm, soft cat food within 10 minutes of recovery (Figure 2). The patient was discharged from hospital four hours after surgery.

Unobserved recovery has been reported as a significant cause of mortality during anaesthesia of small animals (Robertson et al., 2018). The patient must be closely monitored by a designated nurse until discharged from the hospital.

Conclusion

Four weeks after initial surgery, post-operative dental radiography performed under GA displayed the mandibular symphysis to be healed and so the acrylic splint was removed.

Although feline patients may prove more challenging when presented for oral surgery, being prepared, working as a team and being aware of any potential complications and planning how to deal with them can ensure a stress-free, rewarding outcome for both patient and veterinary team.

The benefits for patient, owner and team members that can be gained by fixating a mandibular symphyseal separation or a mandibular fracture with an acrylic splint in comparison to other more invasive methods are also an important note to take home.