Local anaesthesia and Analgesia

Question 1

What is the difference betwee nlocal anaesthesia and local analgesia?

Answer 1

local anesthesia implies that the local anaesthetic is being used as the only means of anaesthetic e.g. cow in standing cesarian
Local analgesia implies that there is general anaesthesia and it is a supplement to general anaesthesia. Local anaesthesia can be used to provide multi modal analgesia along with opioids/NSAIDs

Question 2

What are the three points of the general anaesthesia triad?

Answer 2

narcosis (unconsciousness)
analgesia (antinociception)
Muscle relaxation
In local unconsciousness one doesn’t apply

Question 3

What are the three ways we can achieve local analgesia?

Answer 3

Local anaesthetics
Opioids
a-2 agonists

Question 4

How do local anaesthetic drugs work?

Answer 4

Reversibly prevent the transmission of an action potential along an axon by interfering with sodium channels

Question 5

Which fiber type is most susceptible to local anaethetics?

Answer 5

B fibres - sympathetic

Question 6

Which fiber types are second most sensitive to local anaesthetics?

Answer 6

A-delta fibres (pain)

Question 7

Which fibres are least sensitive to local anaesthetics?

Answer 7

A-beta and A-alpha

Motor and Proprioceptive

Question 8

What is the order in which sensations are lost in local anaesthesia?

Answer 8

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

Question 9

What are the two groups of local anaesthetics?

Answer 9

Esters and amides

Question 10

What are esters metabolised by?

Answer 10

plasma psuedocholinesterases

Question 11

Give an example of an ester

Answer 11

Procaine, tetracaine

Question 12

What are amides metabolised by?

Answer 12

amidases in the liver e.g. lidocaine, bupivicaine, ropivicaine

Question 13

Which is more allergenic.. amides or esters?

Answer 13

Esters, amides are rarely allergenic

Question 14

Which local anaesthetic is licensed in farm animals?

Answer 14

Procaine (an ester)

Question 15

What is the trick for working out if a local anaesthetic is an ester or an amide?

Answer 15

Generally, those with one i in the word are esters

those with two is are the amides

Question 16

Local anaesthetics have two ends - one aromatic ring and one amine. Which is lipophlic?

Answer 16

The aromatic ring is lipophilic, the amine group is lipophobic
What is at the LINK is what makes it an ester or an amide

Question 17

What is the potency determined by?

Answer 17

Lipophilicity

Question 18

What is the duration of action determined by?

Answer 18

The protein binding

Question 19

What determines the speed of onset?

Answer 19

the pKa (dissociation constant, concentration at which drug is 50% ionised)
Important as not ionised portion passes through the membrane. Once inside the membrane will be ionised and will attach to and close the sodium channel

Question 20

What kind of pKa will give you the fastest onset?

Answer 20

close as possible to body’s pH i.e. around 7.4

Question 21

What can you add in with local anaesthetics to make them stick around in the area longer?

Answer 21

Adrenaline

Question 22

What are the complications of local anaesthetics?

Answer 22

Nerve damage (very low incidence)
Systemic toxicity (draw back!)
Local toxicity (very rare)

Question 23

What will it feel like if you try and inject into the nerve?

Answer 23

Very firm pressure. Withdraw and re-do

Question 24

What is the normal dose and toxic dose for lidocaine?

Answer 24

Normal 5mg/kg

toxic 10-20mg/kg

Question 25

What are the first signs you see with over dose?

Answer 25

CNS toxicity (sedation, tremors, seizures) WON'T NOTICE UNDER GA then CV toxicity then CV arrest

Question 26

What happens to iron in methaemoglobin?

Answer 26

Fe2+ in haemoglobin oxidised to Fe3+ | Cannot bind and carry oxygen

Question 27

What anaesthetic is commonly used in the eye?

Answer 27

proxymetacaine (proparacaine) | Warning: slows corneal healing

Question 28

What does EMLA stand for?

Answer 28

Eutectic Mixture of Local Anaesthetics

Question 29

What drugs are in EMLA cream?

Answer 29

Lidocaine and Prilocaine

Question 30

How long does EMLA cream take to take effect?

Answer 30

About 30 mins

Question 31

Which spaces do you need to block in a cow with intervertebral local if you are going to do surgery in the abdomen?

Answer 31

T13, L1 and L2

Question 32

How do you locate the cornual branch of the lacrimal nerve in cows?

Answer 32

Halfway between lateral canthus and hornbud

Question 33

If you are going for an epidural block but you get csf, what can you do?

Answer 33

Withdraw and re-do | Inject half the amount into the CSF

Question 34

WHy don't you inject the same amount if you go into the CSF as if you were in the epidural space?

Answer 34

CSF moves around, don't want it to reach higher structures like the brain etc

Question 35

What is the benefits of epidural anaesthesia?

Answer 35

Relatively simple Good analgesia during and after surgery Decreased stress response to anesthesia and surgery Can decrease the general anaesthetic agents

Question 36

Which drugs can we use in the epidural space?

Answer 36

Local anaesthetics (smalls) Opioids and alpha 2 - large animals Ketamine, NSAIDs

Question 37

Why do you tend not to use local anaesthetics in epidural in horses?

Answer 37

Long lasting, if still acting in recovery it is a disaster, horse can't use back legs and panics

Question 38

What approach do you generally use for epidural anaesthesia in smalls?

Answer 38

Lumbosacral

Question 39

What approach do you generally use for epidural in large animals?

Answer 39

Sacro-coccygeal

Question 40

What are the four scenarios in which yo uwill not do epidural?

Answer 40

Sepsis Infection at injection site Coagulopathy Hypotension/hypovolaemia

Question 41

Why should you monitor urination after an epidural?

Answer 41

Frequent complication - motor block to urinary bladder, May rupture