Drugs in Anaesthesia

Question 1

What are the three phases of hypnosis in general anaesthesia?

Answer 1

Induction
Maintenance
Recovery

Question 2

What are the two modes of administering induction agents?

Answer 2

Intravenous

Inhalational

Question 3

List three commonly used intravenous induction agents.

Answer 3

Ketamine
Propofol
Thiopentone

Question 4

What is thiopentone and how long does it last?

Answer 4

A short acting barbiturate (metabolises slowly, redistributes quickly). Lasts 5-15 mins, cumulative with repeated administration

Question 5

Propofol in induction

Answer 5

A non barbiturate induction agent, characterised by rapid recovery and non-accumulation (therefore can be given in repeated doses or by infusion over long periods)

Question 6

Ketamine in induction

Answer 6

Profound analgesia with superficial sleep (dissociative anaesthesia) + little cardiovascular or respiratory depression and muscle tone is retained

Main use nowadays is for analgesia

Question 7

What is the mechanism of action of propofol?

Answer 7

Unclear

Question 8

What is the mechanism of action of ketamine?

Answer 8

Non-competitive antagonist of the NMDA receptor

Question 9

What are the two most commonly used inhalational induction agents?

Answer 9

Sevoflurane

Halothane (historical but still in use)

Question 10

How can maintenance GA agents be administered? (2)

Answer 10

Intravenous or inhalational

Question 11

Relationship of solubility to speed of induction of inhalational maintenance agents

Answer 11

Agents of high solubility (in blood) give a slow induction - speed depends mainly on ventilation

Agent of low blood solubility give a rapid induction - speed influenced mainly by cardiac output

Question 12

What is a MAC value? What is it related to?

Answer 12

(1) Minimum alveolar concentration - the concentration of a maintenance agent needed to prevent reflex movement in response to an incision in 50% of subjects - used to compare potencies of different inhalational agents.
(2) Related to lipid solubility (expressed as oil/gas partition coefficient) - the greater the lipid solubility, the greater the potency and the lower the MAC value

Question 13

List 5 inhalational agents used for hypnosis maintenance in GA

Answer 13

Nitrous oxide
Halothane
Isoflurane
Sevoflurane - most popular?
Desflurane

Question 14

Describe how sevoflurane works

Answer 14

Rapid onset and recover - neither pungent nor irritant to the respiratory tract (unlike isoflurane and desflurane), useful for gas induction

Question 15

Describe the two main groups of muscle relaxants

Answer 15

Competitive/non-depolarising - work by competitive antagonism of ACh at nicotinic receptors at the NMJ

Non-competitive/depolarising - cause prolonged depolarisation of muscle membrane so that nerve impulses and ACh release are unable to initiate muscle contraction

Question 16

List 6 types of competitive muscle relaxants. Which is most popular?

Answer 16

Rocuronium - most popular (duration of 8-20 mins)
Pancuronium
Vecuronium
Atracurium
Cis-atracurium
Mivacurium

Question 17

What is the role of anticholinesterases in the use of muscle relaxants?

Answer 17

Used to reverse muscle relaxants!

When muscle relaxants are used - patients need to be ventilated, but it is impractical to keep ventilating/waiting until muscle relaxant wears off.

The effect of competitive muscle relaxants can be overcome by excess agonist (i.e. acetylcholine). Anticholinesterase = inhibits breakdown of ACh = The more ACh available = muscle relaxant pushed off receptor.

Question 18

Which anticholinesterase is used commonly in the reversal of muscle relaxants?

Answer 18

Neostigmine - duration of action of 40-60 mins

Question 19

What needs to be considered in the use of anticholinesterase in the reversal of muscle relaxants?

Answer 19

Inhibiting ACh breakdown = increased parasympathetic activity = SLUDGE

Question 20

What is sugammadex?

Answer 20

Used for reversal of neuromuscular blockade induced by the steroidal neuromuscular blocking agents (rocuronium, vecuronium, pancuronium), forms very tight stable complexes with relaxants

Useful in can’t intubate, can’t ventilate scenario where rocuronium etc. has inadvertently already been given (NB CHECK VENTILATION IS POSSIBLE BEFORE GIVING A COMPETITIVE MUSCLE RELAXANTS)

Question 21

What is the only non-competitive muscle relaxant used at present?

Answer 21

Suxamethonium

Question 22

When is suxamethonium used?

Answer 22

Whenever rapid and profound neuromuscular blockade is required to facilitate ETT
e.g.

in RSI (whenever patient is at risk of regurgitation of stomach contents)

Question 23

List three important adverse effects of suxamethonium

Answer 23

1. Sux myalgia
2. Sux apnoea (6% of population metabolise drug excessively slowly)
3. Malignant hyperthermia

Question 24

List 8 indications for rapid sequence induction.

Answer 24

1. Trauma patient
2. Patient with full stomach
3. Patient in pain
4. Patient with any intra-abdominal pathology
5. Pregnany
6. Patient with uncontrolled GORD
7. Diabetic patient with autonomic dysfunction of GI tract
8. Obese

Question 25

List 6 types of local anaesthetics

Answer 25

``` Procaine Cocaine Tetracaine (amethocaine) Lignocaine Bupivacaine Ropivacaine ```

Question 26

When is cocaine used as a local anaesthetic?

Answer 26

Topically to anaesthetise and vasoconstrict nasal tissue

Question 27

When is tetracaine (amethocaine) used as a local anaesthetic?

Answer 27

Topical eye drops

Question 28

Which local anaesthetics can be used in an epidural?

Answer 28

Lignocaine Bupivacaine Ropivacaine

Question 29

Which local anaesthetic is the most cardiototoxic and why?

Answer 29

Bupivacaine - geater lipid solubility, results in slow dissociation of drug from cardiac sodium channels (fast in, slow out)

Question 30

How do local anaesthetics work?

Answer 30

Bind to receptor on sodium channels along nerve cell, leading to reduced sodium conductance and transmission of nerve impulses