Anaesthetics

Question 1

Name the inhalational and IV agents

Answer 1

Inhalational:

• nitrous oxide
• isoflurane
• (desflurane)
• (sevoflurane)

IV

• propofol
• ketamine

Question 2

What are the effects of anaesthesia?

Answer 2

Sedation up to unconsciousness
Amnesia
Muscular relaxation
Reflex suppression and immobilisation
Anxiolysis
Analgesia

Question 3

How does general anaesthesia work (generally)

Answer 3

Reversible inhibit sensory. motor and sympathetic nerve transmission in the CNS to produce unconsciousness and absence of sensation

Question 4

Which parts mediate the different effects of anaesthesia?

Answer 4

Immobilisation - spinal cord

Inhalation anaesthetics work at

• the thalamus - unconsiousness
• the hippocampus - amnesia

Question 5

What is important to predict potency?

Answer 5

Lipid solubility - affects their ability to dissolve and enter cell membranes

Question 6

What is potency?

Answer 6

The concentration of a drug needed to attain 50% of it’s maximal effect

Question 7

What are the two main excitatory and inhibitory neurones needed in consciousness

Answer 7

Excitatory: glutamate

Inhibitory: GABA

Question 8

Mechanism of action of propofol?

Answer 8

Agonises GABA, increases the sensitivity

This increases Cl- influx, hyperpolarising the neurone, decreasing its excitability

Stops depolarisations that would cause pain and increased consciouness etc.

Question 9

What are the effects of propofol?

Answer 9

Potentiating GABA causes

• anxiolysis
• sedation
• anaesthesia

Question 10

What is the effect of potentiating glycine (inhibitory neurotransmitter)

Answer 10

Signalling inhibitory neurotransmission in the spinal cord and brainstem
Reduces response to noxious stimuli

Question 11

What is the effect of inhalational anaesthetics binding to and inhibiting nicotinic ACh receptors?

Answer 11

No Na+ influx
Less depolarisation so less excitation

-analgesia and amnesia (not sedation)

Question 12

Which neurotransmitter acts on NMDA receptors?

Answer 12

Glutamate

Question 13

Which anaesthetics exert their effects on NMDA receptors?

Answer 13

Nitorus oxide

Ketamine

Question 14

What do nitrous oxide and ketamine do at NMDA receptors?

Answer 14

They bind to NMDA LGIC receptors to reduce Ca2+ influx

Less excitation

Question 15

Which are the only anaesthetics not to potentiate GABA?

Answer 15

Xenon
Nitrous oxide
Ketamine

Question 16

What are inhaled agents combined with before being inhaled?

Answer 16

Oxygen, air and often nitrous oxide

Question 17

What is the definition of MAC?

Answer 17

Minimum alveolar concentration

-the percentage of inhaled anaesthetic that abolishes response to surgical incision in 50% of patients

Question 18

What does it mean if an inhaled agent has a low MAC?

Answer 18

It is more potent - MAC relates to its lipid solubilty

Question 19

What are standard MAC doses given to patients?

Answer 19

1.2-1.5

Question 20

What can reduce the MAC?

Answer 20

When a drug is given in combination with other agents such as nitrous oxide or fentanyl (opiate)

Question 21

What is the blood-gas co-efficient?

Answer 21

The degree of absorption across the alveoli into the blood - this has a direct effect on the concentration of drug that reaches target sites in the CNS

Describes the volume of gas in litres that can dissolve in 1L of blood

Question 22

What does it mean if a drug has a high blood gas co-efficient?

Answer 22

The more readily it will enter the blood

Question 23

What does distribution of anaesthetics depend on?

Answer 23

The relative blood supply to each organ or tissue

The specific tissue uptake capacity for the anaesthetic

Question 24

What does the tissue-blood partition co-efficient determine?

Answer 24

How readily the anaesthetic will move from the blood to a specific tissue type

Question 25

How are inhaled agents eliminated?

Answer 25

As conc in the blood drops, the anaesthetic moves out of the cell membranes, into venous blood, back to alveolus to be eliminated unchanged Eliminated from well-perfused tissues first (brain, kidneys), then muscle, then fat Fat and muscle can be large reservoirs, and as it diffuses out of these compartments, can enter the CNS, affecting consciousness

Question 26

What is the duration of recovery from inhaled agents proportional to?

Answer 26

Length of procedure | Degree of loading of muscle and fat compartments

Question 27

Why are IV anaesthetics combined with inhaled ones?

Answer 27

Reduces time taken to reach anaesthetic depth sufficient for surgery Bypasses the excitement/aggression of stage II

Question 28

Protein binding of inhaled and IV agents?

Answer 28

Inhaled - low | IV - high (98%)

Question 29

Distribution of IV agents?

Answer 29

Rapidly to the CNS (well perfused) | Drug redistributes throughout the circulation into muscle and fat - large capacity for lipophilic drugs

Question 30

Metabolism and elimination of IV agents (propofol)

Answer 30

Hepatic and extra-hepatic conjugation | Half-life around 2 hours

Question 31

ADRs of general anaesthesia?

Answer 31

Post-operative nausea and vomiting (opioids) CVS - hypotension Post-operative cognitive dysfunction - increases with age Chest infection

Question 32

ADRs of local anaesthetics?

Answer 32

Can block heart depolarisation | Anaphylaxis

Question 33

Uses of benzodiazepines in general anaesthesia?

Answer 33

Low dose a few hours before surgery - anxiolytic High dose - sedation for short procedures

Question 34

Uses of propofol?

Answer 34

Rapid IV induction of anaesthesia

Question 35

Uses of nitrous oxide?

Answer 35

Contributes to analgesia via NMDA receptors Reduces the effective MAC of flurane Minimises recovery time

Question 36

Uses of opiates (and which ones) in anaesthetics?

Answer 36

Morphine and fentanyl Produce analgesia Fentanyl more potent than morphine Induces analgesia almost immediately Finer control of analgesic effect in surgery Reduce MAC Reduce risk of CVS depression by flurane

Question 37

What are the two classes of drugs that abolish reflexes and induce muscle relaxation?

Answer 37

Competitive nicotinic ACh receptor antagonists - tubocurarine - pancuronium Nicotinic ACh receptor depolarising agonists -succinylcholine Flurane also potentiates neuromuscular relaxation

Question 38

What are the different depths of anaesthesia?

Answer 38

1: Analgesia - due to effects on spinothalamic tract 2: Excitement - delirium and aggressive behaviour, now uncommon due to propofol 3: Surgical anaesthesia - CNS depression, muscles relaxed 4: Death - due to medullary depression leading resp and cardiac arrest