Local anaesthetic blocks

Question 1

Local anaesthetics have a narrow therapeutic index. What does this mean?

Answer 1

We use local anaesthetics at quite close to their toxic dose.

If we do multiple blocks/may need further down the line, we need to be careful that the sum of these doses does not reach the toxic dose.

Question 2

What local anaesthetics might you use in small animal practice?

Answer 2

• Lidocaine - licensed in dogs and cats
• Bupivacaine - not licensed; has a longer duration of action than lidocaine

Question 3

What local anaesthetics might you use in cattle?

Answer 3

• Procaine
• Lignocaine - can be used off-licence but must justify this under cascade

Question 4

What local anaesthetics might you use in horses?

Answer 4

• Mepivacaine
• Lignocaine - licensed in horses including those for human food chain

Question 5

Dental blocks are great for extractions, but what should you try to avoid doing if possible to prevent the patient injuring themselves in recovery?

Answer 5

• Avoid doing bilateral alveolar blocks with long-lasting anaesthetics as the patient can wake up with an anaesthetised tongue
• If they can’t feel their tongue, they may bite it

Question 6

True/false: you can give local anaesthetics via CRI to provide relief from soft tissue pain,

Answer 6

True

Question 7

What should you use when giving local anaesthetic via CRI?

Answer 7

Only use pure lidocaine.

Question 8

In what species can you give lidocaine IV via CRI?

Answer 8

• Dogs and horses (colic)
• Often used in equine laparotomies because it is analgesic and prokinetic (speeds up the gut which is likely to be slowed down due to surgery)
• Best avoided in cats

Question 9

True/false: providing whole body analgesia via a local anaesthetic give IV (CRI) reduces the MAC of volatile agent required and therefore contributes to balanced anaesthesia.

Answer 9

True

Question 10

What could you administer to a patient with local anaesthetic toxicity?

Answer 10

An intralipid

Question 11

What are the disadvantages of a line block for flank surgery in farm animals?

Answer 11

❌ Requires repeated needle sticks all the way down

❌ All drugs come with adrenaline included and theoretically lots of adrenaline around the incision site is not ideal

❌ Unreliable anaesthesia of the peritoneum

❌ Slow

Question 12

What are the disadvantages of an inverted L block/7 block?

Answer 12

❌ Lots of needle sticks required

❌ Unreliable anaesthesia of the peritoneum

❌ Slow

Question 13

Which nerves do you need to block for flank surgery (when performing a paravertebral block)? How do you perform this block?

Answer 13

• Nerves behind T13, L1, L2. You would also block L3 for a C-section.
• “Walk” off the transverse process

Question 14

How do you test you are in the right place when performing a paravertebral block?

Answer 14

• Let a drop enter the cannula
• It should just sit there
• If it gets sucked down you have probably gone too deep and may be in the abdominal space

Question 15

What blocks could you use for foot surgery?

Answer 15

• Ring block
• Intravenous regional (IVRA) - use a tourniquet and inject into vein
• Local infiltration - fine for mass removal, insufficient for anything more invasive/amputation

Question 16

What blocks could you use for eye surgery?

Answer 16

• Local infiltration/ring block - eyelid surgery
• Retrobulbar block - major eye surgery
• Peterson block - major eye surgery
• Auriculopalpebral block - covers motor supply only!‼️

Question 17

How would you decide between a retrobulbar and Peterson block for major eye surgery?

Answer 17

• Retrobulbar block is technically easier but destructive - good for enucleations
• Peterson block is technically more difficult but much more likely to preserve the structures of the orbit - if you want a functional eye at the end, use this!

Question 18

What blocks could you use for teat surgery?

Answer 18

• Ring block
• IVRA with tourniquet at top of teat
• Paravertebral/epidural
• Local infiltration - locals contain adrenaline and vasoconstriction could cause the teat to slough off; be careful!

Question 19

What blocks could you use for perineal surgery?

Answer 19

• A caudal epidural (1st and 2nd coccygeal vertebrae)