Local Anaesthetics

Question 1

How do they work

Answer 1

Reversible block conduction when applied locally around nerve fibres
- block Na+ channels at nerve endings
Sensory more sensitive than motor

Question 2

Order in which sensations disappear

Answer 2

Pain
Cold
Warmth
Touch
Pressure
*Recovery in reverse order

Question 3

Advantages of using alongside GA

Answer 3

Drug sparing
Minimises CP depression
Faster recovery
Provides analgesia beyond full GA recovery

Question 4

Potential result of overdose of local anaesthetic

Answer 4

bradycardia

Cardiac arrest

Question 5

Reason for addition of epinephrine

Answer 5

Local anaesthetics tend to be vasodilators
Addition of epinephrine produces localised vasoconstriction
Slows diffusion & limits absorption
Lessens risk of toxicity
May increase speed on onset & prolong effects

Question 6

Properties of lidocaine

Answer 6

Extremely stable in solution
Short duration of onset (5-15mins)
Moderate duration of action (1-2hrs)
Can’t be given IV
Cats very sensitive

Question 7

Properties of bupivicaine

Answer 7

Very stable compound
4x more potent than lidocaine
Slower onset (10-20mins)
Longer action (6-8hrs)
Grater potential for cardiotoxicity than lidocaine
Can’t be given IV
Does not require epinephrine

Question 8

Properties of mepivicaine & target species

Answer 8

Equine
Rapid onset (2-4mins)
Short duration (~1hr)
No vasodilation
May cause CP depression & convulsions if given IV or OD

Question 9

Define local infiltration & indications for use

Answer 9

Infiltrated by inj. In close proximity to nerve
Intradermally
Subcutaneously 
Between muscles
Sx involving superficial tissues

Question 10

Define nerve block

Answer 10

Local infiltration technique

Inj. Close to nerve to desensitise particular site

Question 11

Define line block

Answer 11

Local infiltration technique

Inj. Of continuous line immediately proximal to target site

Question 12

Duration of effect dependant on

Answer 12

Drug
Absorption rate by local vessels
Addition of epinephrine

Question 13

Define regional anaesthesia

Answer 13

Inj. Into major nerve plexus or in close proximity to spinal cord
Peripheral nerve stim. May be used to locate appropriate fibres

Question 14

Define epidural, how it works & indications for use

Answer 14

Inj. Into epidural space between L7-S1
Drug circulated between vertebrae & dura mater
Pelvic & tail sx
Hindlimb ortho sx

Question 15

Define spinal anaesthesia

Answer 15

Inj. Through dura into subarachnoid space

Drug mixes w/CSF

Question 16

Define splash block & indication for use

Answer 16

Direct application to target area
Drug dripped onto exposed tissues
E.g. body wall during laparotomy closure

Question 17

Spinal anaesthesia advantages

Answer 17

Ability to desensitise wide sx field

Faster onset than epidural & lower dose req.

Question 18

Spinal anaesthesia disadvantages

Answer 18

Req. technical skill & anatomical knowledge

Risk of iatrogenic damage to nerve tissue

Question 19

Regional anaesthesia advantages

Answer 19

May remove/reduce req. for GA

Accurate method if using peripheral nerves stimulation

Question 20

Regional anaesthesia disadvantages

Answer 20

Req. technical skill & anatomical knowledge

Risk of toxicity

Question 21

Define topical anaesthesia

Answer 21

Application directly to MM

Ocular/nasal/laryngeal

Question 22

Topical anaesthesia advantages

Answer 22

May enable micro sx
E.g. corneal debridemen
allows intubation where laryngospasm a concern

Question 23

Topical anaesthesia disadvantages

Answer 23

Only superficial analgesia

Variable absorption & effectiveness

Question 24

Risks associated with local anaesthesia

Answer 24

Temp/permanent loss of function if inj. Into nerve fibres
Tissue irritation
Self-trauma in recovery
Hypersensitive reactions
System toxicity