Anaesthesia Sandwich Break CPD Questions and Answers
Joanne Michou MA VetMB Dip.ECVAA MRCVS gives you something to think about regarding analgesia for cat dental extractions.
You have a 4kg 5 year old Siamese cat in for a dental. It has a very painful mouth and will most likely need extractions. Clinical examination is otherwise normal.
How can you provide appropriate analgesia?
Always think multimodal analgesia, pre-emptive and preventive analgesia.
If you can provide local analgesia with a nerve block then this is always a good idea as is the only way to completely block the nociceptive signal.
The analgesia should be pre-emptive, administered before the insult, and preventive, in order to reduce postoperative pain and/or analgesic use.
Opioid analgesia can be provided in the premedication as well as Non-Steroidal-Anti-inflammatory-Drugs (NSAID’s) and local nerve blocks.
Both buprenorphine and methadone are licensed for use in the cat. The choice between the two drugs would depend on the degree of ‘pain’ or nociception expected from the procedure and whether other techniques or drugs are to be used in combination. Butorphanol is a poor analgesic so is not recommended.
Buprenorphine (0.02 mg/kg) is a very good analgesic in the cat and would be ideal for a cat undergoing extractions.
Meloxicam, robenacoxib and ketofen are NSAID’s licensed for use in the cat with injectable followed by oral routes of administration. These would be ideal as the patient would be able to go home with post-operative NSAID’s.
Local nerve blocks would provide anaesthesia to the site of extraction. Unpublished data on nerve blocks given to cats undergoing dental extractions, has shown to improve quality of anaesthesia, reduce isoflurane requirement, improve post-operative pain scores and reduce the need for post-operative pain relief in cats. This is compared to cats receiving buprenorphine and meloxicam only.
What local nerve blocks could be performed to remove molars from the maxillary and mandibular arcades?
The most useful would be mandibular nerve block and maxillary nerve block. The syringe must be aspirated prior to injection to prevent accidental vascular injection.
Inferior branch of mandibular alveolar nerve (mandibular nerve block)
Blocks mandibular arcade from caudal horizontal ramus rostrally
All lower dental arcade + mandible
Blocks maxillary arcade from zygomatic arch rostrally
Nose, maxilla, all upper dental arcade
Infraorbital and mental nerve blocks may also be used, but will only block the most rostral parts of the maxilla or mandible
What local anaesthetic would you use and why?
The time spent doing the anaesthetic and extractions needs to be minimised. Lidocaine has a fast onset of action, within 5 minutes, so is ideal in this situation. However, its duration of action is short and in formulations without adrenaline last 1-1.5 hours, whereas with adrenaline last 1.5-2 hours. Lidocaine containing adrenaline solution is licensed for use in the cat.
Alternatives are bupivacaine and ropivacaine, however, their onset of action is 15 and 10 minutes respectively, which is undesirable in this situation. The benefit would be their longer duration of action, 4-6 hours.
What dose and volume of your chosen local anaesthetic would you use and why?
A maximum of 4 mg/kg TOTAL whole body dose in the cat is recommended. This total dose can be split between the nerve blocks needed. The cat weighs 4 kg, therefore a total dose of 16 mg of lidocaine. Lidocaine is formulated as 20mg/kg or 2% solutions, so a total of volume of 0.8 ml should be split between nerve blocks.
This dose is selected to be below the toxic dose of lidocaine in the cat.
Is there anything else you need to consider regarding local anaesthetic and dose administered?
It is worth bearing in mind the lidocaine spray (Intubeaze) used at intubation will also be part of the total dose of lidocaine administered to the cat.
One spray of Intubeaze contains 2-4 mg of lidocaine, therefore only one accurate spray should be used.
What are the clinical signs of local anaesthetic toxicity and at what doses do you see this in the cat?
Neurological signs, such as twitching and seizuring, can occur at approximately 11 mg/kg lidocaine i.v in the cat. However, if the cat is anaesthetised, you will not see these signs, so it is important to calculate the toxic dose and then be well below this, hence the total dose suggested of 4 mg/kg.
This will progress to cardiovascular affects, resulting in ventricular tachycardia, fibrillation and death, at higher doses, 47 mg/kg.
You need to extract teeth from all four quadrants. Can you and do you want to perform nerve blocks on all four quadrants? What are your reasons?
Yes, you can anaesthetised all four quadrants, however, the concern would be inadvertent blockade of the lingual nerve (which may occur during mandibular nerve block) leading to loss of motor function to the tongue and potential trauma in recovery. Given that the duration of action of the lidocaine is short, 1-1.5 hours, this will be unlikely tocause any major problem in recovery.
Thank you to Joanne Michou for compiling these questions and answers