Local anaesthesia and analgesia

Question 1

What is local anaesthesia?

Answer 1

implies that the local anaesthetic is used as the ONLY means of anaesthesia (ex: cow standing c section)

Question 2

What is local analgesia?

Answer 2

provides extra analgesia as a SUPPLEMENT TO GA
can be used to provide multi-modal analgesia

Question 3

What is the triad of general anaesthesia?

Answer 3

narcosis (unconsciousness)
analgesia (antinociception)
muscle relaxation

Question 4

What can we use to achieve local anaesthesia?

Answer 4

local anaesthetic drug
opioids
a2 agonist
ketamine

Question 5

What are local anaesthetic drugs for and how do they work?

Answer 5

reversibly block the transmission of action potentials along an axon and block the transmission of pain
suppress action potentials in excitable tissues by blocking voltage gated Na channels

Question 6

What are the most to least sensitive to local anaesthetic nerve types ?

Answer 6

most: B fibres (sympathetic)
A delta fibres (sensory pain)
least: Abeta and Aalpha (motor and proprioceptive)

Question 7

What sensations are lost in what order with differential block?

Answer 7

1. pain
2. cold
3. warmth
4. touch
5. deep pressure

Question 8

How are esters metabolised?

Answer 8

by plasma pseudocholinesterases

Question 9

How are amides metabolised?

Answer 9

in liver by amidases

Question 10

How does chemical structure affect pharmacology?

Answer 10

Lipid solubility determines potency
protein binding determines duration of action
pKa determines speed of onset (closer to pH of tissue = faster)

Question 11

What are examples of ester local anaesthetics?

Answer 11

procaine
tetracaine

Question 12

What are examples of amide local anaesthetics?

Answer 12

lidocaine
bupivacaine
ropivacaine

all have 2 “i”s

Question 13

Which local anaesthetic has low and high potency?

Answer 13

procaine: low lipid solubility = low potency
tetracaine: high lipid solubility = high potency

Question 14

Which local anaesthetic has slow and fast onset?

Answer 14

procaine: highest pKa = slow
mepivacaine: lowest pKa = fast

Question 15

Which local anaesthetic has a short or long duration?

Answer 15

procaine: low protein binding = shorter duration (60-90min)
bupivacaine: high protein binding = longest duration (180-500min)

Question 16

Which local anaesthetics can be used in food producing animals?

Answer 16

procaine is only licensed drug in UK for cattle only

Question 17

Which local anaesthetic can be used in horses?

Answer 17

all if licensed or is on the positive list
mepivacaine mainly used
lidocaine can caused skin and SC swelling

Question 18

How are local anaesthetics absorbed?

Answer 18

applied directly to site of action
systemic absorption partly controls duration

Question 19

What can be added to local anaesthetics to reduce systemic absorption?

Answer 19

Vasoconstrictor (adrenaline) reduces systemic absorption
reduces local blood flow
increases duration of action

Question 20

What are potential complications of using local anesthesia?

Answer 20

nerve damage
systemic toxicity
local toxicity

Question 21

What are the toxic doses for lidocaine, bupivacaine and ropivacaine?

Answer 21

lido: 10-20 mg/kg (normal 5)
bupi: 3.5-4.5 mg/kg (normal 2)
ropi: 5 mg/kg (normal 1.5)

Question 22

What are the signs of local anaesthetic toxicity as the blood concentration increases?

Answer 22

first CNS toxicity: sedation, tremors, seizures
then CVS toxicity: direct action on heart and peripheral vasculature, indirect action by blocking autonomic nerves
finally CV arrest

Question 23

What are other types of toxicity that can be caused by local anaesthesia?

Answer 23

allergy
methaemoglobinaemia

Question 24

What is methaemoglobinaemia

Answer 24

type of toxicity

iron in haemoglobin is oxidised, can’t bind to carry oxygen
causes cyanosis

Question 25

What are types of local anaesthetics given as eye drops?

Answer 25

proparacaine
tetracaine

Question 26

What should we consider when prescribing eye drop local anaesthesia?

Answer 26

can slow corneal healing

Question 27

What types of local anaesthetics can be given as skin creams?

Answer 27

Eutectic Mixture of Local Anaesthetics EMLA
lidocaine
prilocaine

Question 28

How is skin topical local anaesthetic used?

Answer 28

used for venous catheter
absorbed across intact skin
apply 30 min before

Question 29

What types of local anaesthetics are given as infiltrative anaesthesia?

Answer 29

lidocaine with or without adrenaline

Question 30

What should we consider when using infiltrative local anaesthetics?

Answer 30

use lowest possible concentration
fine sharp needles
don’t use versions with adrenaline in tissues supplied by end arteries (ears, tails, etc.)

Question 31

What are the types of field blocks?

Answer 31

line blocks
inverted L block

Question 32

What are the problems we can run into when using paravertebral anaesthesia?

Answer 32

fat animals
muscle spasm
damage to aorta
infection

Question 33

Where is the cornual nerve block given and why?

Answer 33

for disbudding

cattle: cornual branch of lacrimal nerve, halfway between lateral canthus and horn bud
goat: cornual branch of intratrochlear nerve halfway between medial canthus and horn bud

Question 34

What are cranial peripheral nerve blocks that can be given and what do they affect?

Answer 34

mandibular nerve: teeth and lower lip
infraorbital nerve: upper lip and nose
supreaorbital and auriculopalpebral nerves: eye
retrobublbar block: eye enucleation

Question 35

What are the potential forelimb peripheral nerve block and what do they affect?

Answer 35

cervical palpebral: shoulder, brachium
axillary approach to brachial plexus: elbow distally
radial, ulnar, median, musculocutaneous: elbow distally
radial, ulnar, median: carpus distally
IVRA/bier’s block: below tourniquet

Question 36

What are potential hindlimb peripheral nerve blocks and what do they affect?

Answer 36

lumbar and sacral plexus block: whole limb
femoral/sciatic: stifle distally
IVRA/bier’s block: below tourniquet

Question 37

What are the advantages of epidural anaesthesia?

Answer 37

relatively simple technique
good analgesia intra and post op
decreased stress response to anaesthesia and surgery

Question 38

What are indications for use of epidural anaesthesia?

Answer 38

abdominal and hind quarter surgery in SA under light GA
standing surgery in farm animals and horses
postop analgesia for above surgeries or injuries

Question 39

What drug types can be used for epidural anaesthesia?

Answer 39

local anesthetics
opioids
alpha 2 agonists
ketamine, nsaids

Question 40

Where are epidurals given in SA?

Answer 40

lumbo sacral site

Question 41

where are epidurals given in LA?

Answer 41

caudal site: sacro-coccygeal or Co1-Co2

Question 42

What are contraindications to epidural anaesthesia?

Answer 42

sepsis
infection at injection site
coagulopathy
hypotension/hypovolemia
distorted anatomy

Question 43

What are potential complications to epidural anaesthesia?

Answer 43

nerve damage
pruritus
urinary retention
motor dysfunction
accidental vascular injection
haematoma formation
infection
hypotension
resp depression due to cranial spread

Question 44

What are the indications for IVRA biers block?

Answer 44

analgesia for surgery of the distal limb

Question 45

How do we perform intravenous regional anesthesia/bier’s block?

Answer 45

exsanguinate limb distal to surgical site
apply tourniquet
inject lidocaine into distal vein
effect dependent on tournique
limit of 2h due to ischaemia of distal tissue

Question 46

What are the actions in the body of systemic local anesthetic?

Answer 46

lidocaine (can be used IV)

anti-arrhythmic properties
analgesia
prokinetic (equine colic)
free radical scavenger