Lecture 10

Question 1

What is meant by the term anaesthesia?

Answer 1

Refers to a generalised reversible depression of the CNS. Results in the decreased perception of pain however decreased perception of pain does not make anaesthetics analgesics.

Question 2

What is the purpose of injectable anaesthetics?

Answer 2

1. Usually used to induce anaesthesia prior to gaseous anaesthetic maintenance
2. Sometimes, especially large animals or short procedures it is used for the maintenance of anaesthesia

Question 3

What is the main uses of the barbiturates?

Answer 3

decrease CNS excitability via GABA agonism. This makes them well suited to clinical roles of anticonvulsion, injectable general anaesthesia and humane euthanasia

Question 4

What length of time does thiopentone act over and what is an important clinical consideration when giving this drug?

Answer 4

Ultra short acting anaesthetic. The dose distributed to the brain and has an anaesthetic effect. Minutes later lots of drug distributes away from the brain to less perfused organs (e.g. muscle). Giving a second dose will reduce the speed at which this happens and hence the recovery time will increase.

Question 5

What types of breeds should thiopentone be avoided in?

Answer 5

Thiopentone should be avoided in thin and skinny breeds (particularly sighthounds)

Question 6

What type of solution and thiopentone contained in? what does this mean when administering it?

Answer 6

Thiopentone needs to be in a highly alkaline solution to maintain solubility. This means it is important to get it into the vein.

Question 7

What is the primary use of pentobarbitone?

Answer 7

Pentobarbitone is mainly used in a euthanasia solution. It is given IV to lead to quick overdose of the animal.

Question 8

What is propofol?

Answer 8

GABA agonist

Question 9

What is a benefit of using propofol?

Answer 9

Rapid and smooth induction of anaesthesia seen alongside a smooth recovery from it. It is rapidly taking up by the brain and it is then quickly and extensively metabolised.

Question 10

What is unique about the drug propofol? (think about the colour of the solution)

Answer 10

A white liquid that goes directly into a vein

Question 11

What is the effect of Alfaxalone?

Answer 11

GABA agonist. A smooth induction of anaesthesia is seen and there is no cumulative effect meaning it is possible to provide top-ups. Also excellent smooth recovery from anaesthesia.

Question 12

What is the mechanism of dissociative anaesthesia?

Answer 12

antagonism at NDMA receptors. Disassociation the patient is grossly unresponsive, yet no asleep.

Question 13

How can ketamine be given?

Answer 13

Ketamine has very good non-IV bioavailability. Hence it is capable of inducing general anaesthesia when given intramuscularly or subcutaneously.

Question 14

Provide an example of a drug where the strength of the reflexes cannot be used to asses the depth of anaesthesia.

Answer 14

Ketamine. Many reflexes persist where the other general anaesthetics dull the reflexes and therefore the reflexes can act as a guide to the depth of anaesthesia.

Question 15

Provide an example where barbiturates should not be used:

Answer 15

Should not be used for liver failure and should not be used in caesareans

Question 16

Why should ketamine not be used by itself?

Answer 16

No CVS depression effects of Ketamine. Hence use by itself causes a very stormy recovery.

Question 17

What are the two inputs in a gas anaesthetic?

Answer 17

1. Oxygen

2. Anaesthetic gas

Question 18

The is the MAC (minimum alveolar concentration)?

Answer 18

The minimum concentration of anaesthetic that is required to anaesthetise the patient.

Question 19

Describe the purpose and the mechanism of action of local anaesthetics:

Answer 19

They work by blocking conduction of nerve action potentials (AP’s). The local anaesthetic binds to receptor site on the neurons Na channel causing the sodium channel to close. As a result no nerve conduction occurs.

Question 20

Why is there variation in speed of onset of action and duration of action?

Answer 20

Due to differences in affinity for receptors.

Question 21

What is a local anaesthetic that would be effective in cow Caesareans?

Answer 21

Lignocaine

Question 22

When would the local anaesthetic Bupivacaine be used?

Answer 22

good in epidurals. Has a slow onset of action, do not use when rapid desensitisation is required.

Question 23

When should the local anaesthetic Mepivacaine be used?

Answer 23

Less irritating than lignocaine, used for nerve blocks in lame horses.

Question 24

When should the local anaesthetic proxynetacaine be used?

Answer 24

Good topical anaesthetic for ocular examination.

Question 25

What are the potential heart implications of giving very high doses of a local anaesthetic?

Answer 25

myocardial depression, vasodilation that then leads to hypotension and dysrhythmias