Anaesthetic Drugs

Question 1

Do anaesthetics work in the same way?

Answer 1

No - is no universal mechanism. Different anaesthetics work in different ways.

Question 2

What is the triad of anaesthesia?

Answer 2

The use of drugs to produce amnesia, analgesia and akinesia - which in turn lightens the load of amnesia (anaesthetic) drugs that need to be given to the patient.

Question 3

What is the medical term for unconsciousness?

Answer 3

Anaesthesia

Question 4

What is the medical term for muscle relaxation?

Answer 4

Akinesia

Question 5

What is the medical term for pain relief?

Answer 5

Analgesia

Question 6

Do we know how anaesthetic drugs work?

Answer 6

No

Question 7

Name four potential sites that anaesthetic drugs are thought to target in the body.

Answer 7

Cerebral cortex
Thalamus
Reticular activating system
Spinal cord

Question 8

Which receptors do we think anaesthetic drugs potentially have an impact upon?

Answer 8

GABA & glutamate receptors
Voltage-gated ion channels
Glycine & serotonin receptors

Question 9

What do anaesthetic agents do to excitable tissues?

Answer 9

Suppress them to varying degrees

Question 10

What type of solubility do anaesthetic drugs need to have?

Answer 10

Need to be lipid soluble

Question 11

What is the name of the correlation between lipid soluble drugs and potency?

Answer 11

Meyer-Overton correlation

Question 12

What does the Meyer-Overton correlation say?

Answer 12

The more lipid-soluble a drug the more potent it is.

Question 13

Name three inhaled anaesthetic drugs

Answer 13

Sevoflurane
Isoflurane
Desflurane

Question 14

What are propofol, thiopentone, etomidate & ketamine used for?

Answer 14

IV anaesthetic drugs

Question 15

Which is the main IV anaesthetic drug used?

Answer 15

Propofol

Question 16

What is balanced anaesthesia?

Answer 16

Using the triad of drugs (analgesia, akinesia & anaesthetics) meaning that you dont have to use too much of one drug and therefore kill the patient.

Question 17

Why is it important that anaesthetic drugs are lipid soluble?

Answer 17

It means that they can cross the BBB

Question 18

What chemical family are inhaled anaesthetics from?

Answer 18

Halogenated ethers

Question 19

What are the advantages to propofol as a drug?

Answer 19

Easy to administer
Doesnt harm the vein
Lipid soluble
Rapidly perfuses the brain & relaxes the larynx
Antiemetic & Antiepileptic
Can maintain anaesthestia with infusion or repeated bolus
Does not accumulate
Rapidly metabolised by the liver

Question 20

What are the disadvantages to propofol as a drug?

Answer 20

Can cause pain on injection & abnormal movements
Can cause hypotension
Is an infection risk due to the lipid it is stored in

Question 21

How does propofol wear off and allow P to wake up?

Answer 21

It is redistributed into the tissues - this allows P to wake up.

Ps DO NOT wake up because it is metabolised.

Question 22

Where is propofol redistributed to?

Answer 22

Less perfused tissues - such as muscle. However fat levels of the drug remain low because fat is very poorly perfused

Question 23

What is the name of the effect that is used in vaporiser bottles?

Answer 23

Plenum effect

Question 24

Name three types of inhalational anaesthetics

Answer 24

Halogenated ethers
Nitrous oxide
Xenon

Question 25

How are inhalational anaesthetics administered?

Answer 25

Through specific vaporisers which heat up the drug to its specific boiling point and vaporise it.

Question 26

What is the theoretical maximum inspired concentration?

Answer 26

70-80%

Question 27

What happens to the patient initially when using a halogenated ether? What is this termed?

Answer 27

Analgesia Excitement (may fight the mask) then Surgical anaesthesia Termed etherisation

Question 28

What are the risks of using inhaled anaesthetics?

Answer 28

Post-op nausea & vomiting (PONV) If irritation - can make gas induction difficult (e.g. coughing) Emergence phenomena - awaking during operation but being unable to move

Question 29

Why is it important that the ideal inhalational agent is not metabolised?

Answer 29

Because to metabolise it runs an increased risk of acute hepatitis

Question 30

What do muscle relaxants do?

Answer 30

Block neuromuscular junction receptors and stop muscles from working - thereby causing paralysis and cessation of breathing

Question 31

Who should be given muscle relaxants?

Answer 31

Unconscious patients only

Question 32

Why do we use muscle relaxants?

Answer 32

- To assist with intubation - To facilitate surgery or ventilation

Question 33

What are the two classes of muscle relaxants?

Answer 33

Depolarising and non-depolarising

Question 34

How do depolarising muscle relaxants work?

Answer 34

Depolarising muscle relaxants bind to the ACh receptor on the post-synaptic membrane. They cause initial depolarisation of this membrane, and then as they do not release - this means the post-synaptic receptor is blocked and cannot be stimulated again.

Question 35

Name one depolarising neuromuscular blocking agent (NMBA).

Answer 35

Succinylcholine

Question 36

How rapid is succinycholine in its action?

Answer 36

Binds rapidly Half-life of about 2 mins Wears off in around 5 mins

Question 37

What is succinylcholine metabolised by?

Answer 37

Plasma cholinesterase

Question 38

What are the negatives to using succinylcholine?

Answer 38

Has multiple side effects - Fasciculations - Anaphylaxis - K+ - Cholinesterase abnormality... - Causes fasciculations which can cause post-op pain for the patient - Higher rate of anaphylaxis - Can increase levels of K+ in the blood - If P has abnormality and doesnt produce cholinesterase - means P can remain paralysed for a few hours (rare)

Question 39

How do non-depolarising NMBAs work compared to depolarising ones?

Answer 39

Non-depolarising compounds bind to the post-synaptic receptors competitively but DO NOT cause depolarisation of the post-synaptic membrane

Question 40

What type of compounds are used as non-depolarising agents?

Answer 40

Quaternary ammonium compounds

Question 41

How do non-depolarising agents vary in speed from depolarising agents?

Answer 41

Non-depolarising agents have slower onset and offset times

Question 42

Name one non-depolarising agent used.

Answer 42

Rocuronium (aslo - vecuronium, pancuronium, benzylisoquinolinium and atracurium)

Question 43

What are NMBAs used for?

Answer 43

Intubation Surgery Ventilation ECT Transfer of patients Lethal injection

Question 44

Do we usually reverse depolarising agents?

Answer 44

Usually not - as effects wear off quickly. However if there is prolonged paralysis due to cholinesterase deficiency then yes - may need to reverse

Question 45

Which drug do we commonly use to reverse non-depolarising agents?

Answer 45

Neostigmine

Question 46

How does neostigmine work?

Answer 46

Binds to acetylcholinesterase - thus preventing the breakdown of ACh in the cleft

Question 47

Which drug is used for reversal of NMBAs but is very expensive?

Answer 47

Sugammadex

Question 48

How does botulinum work?

Answer 48

Prevents vesicles containing ACh from binding to the membrane - therefore preventing the release of ACh into the synaptic cleft

Question 49

What is Botulinum used for?

Answer 49

Relief of muscle spasms and contractions Neuropathic pain Aesthetic uses