Local anaesthetics

Question 1

Lignocaine
- Onset of action
- DOA
- 4 different preparations

Answer 1

Local anaesthetic
- commonly used
- stings
- rapid onset of action (2-3mins)
- short DOA (1-2hrs)

Lignocaine with Adrenaline = Injectable
- adrenaline-mediated alpha-1 agonism causes vasoconstriction, prolonging DOA of local anaesthetic
- BEWARE - vasoconstricting end arteries- so don’t use in teats or digits

Lignocaine with Phenylephrine = Spray
- spray on larynx of cat = desensitization - prevents laryngospasm

Lignocaine + Bupivacaine + Adrenalin + Cetrimide = “Tri-solfen” = Gel based spray
- Lignocaine takes effect quickly
- Bupivacaine - slow to take effect but long DOA - therefore 90d WHP
- Adrenalin - prolongs DOA
- Cetrimide - antiseptic

“Numocaine”/”Numbnuts”
- Elastrator combined with a lignocaine delivery system
- Used for 2-10wk old lamb castration and tail docking

Question 2

Mepivicaine
- Preparation type
- Why is it better than lignocaine
- When is it commonly used?

Answer 2

Local anaesthetic = Injectable
- less irritating than lignocaine
- for nerve blocks in lame horses

Question 3

Bupivicaine

Answer 3

Local anaesthetic = injectable
- long acting (3-6hrs)
- good for epidurals
- slow onset of action (6-10mins)
- concerns with cardiotoxicity

Question 4

Ropivacaine (“Naropin”)

Answer 4

Local anaesthetic
- long acting (2-4hrs)
- slow onset of action (6-10mins)
- safer than bupivicaine

Question 5

Proxymetacaine (“Alcaine”)

Answer 5

Local anaesthetic = injectable
- topical anesthetic for ocular examination

Question 6

EMLA

Answer 6

Eutectic mix of local anaesthetic
Local anaesthetic = topical oil preperation
- A topical oily product - easily absorbed through the skin
- Onset of action ~1hr
- DOA ~1-2hrs

Question 7

Toxicity of LAs

Answer 7

• Common overdose bcs people dont wait long enough
• CNS most sensitive target
• low dose = suppression of inhibitory neurons
• high dose = overall CNS suppression: sedation AND affects heart
  Myocardial depression, vasodilation –> hypotension
  Dysrrythmias

Question 8

LAs MOA

Answer 8

Bind to receptor site on neurons Na channel –> Na channel closes –> no nerve conduction

Question 9

How can lignocaine be used other than for local anaesthesia?

Answer 9

Can be used as an antiarrhythmic

Can be used systemically
- Eg for equine colic - post operative prokinetic, anti-inflam and analgesia

Question 10

What LA has the longest DOA?

Answer 10

Bupivacaine

Question 11

Why would a LA be used alongside a GA?

Answer 11

Just bcs an animal is anaesthetized doesn’t guarantee it has appropriate analgesia
LAs decrease nociception
= smoother anaesthetic and more comfort