Session 9: Anaesthesia

Question 1

Give broad types of anaesthesia.

Answer 1

General or local

Question 2

Types of general anaesthesia.

Answer 2

Inhalation/volatile

Intravenous

Question 3

Give examples of conscious sedation.

Answer 3

Small amounts of anesthetic or benzodiazepines to produce a sleepy-like state.

Question 4

Explain the process of anaesthesia before, during and post-surgery.

Answer 4

Premedication of something sedative/hypnotic such as benzodiazepine.

Induction usually intravenous but can also be inhalational to put the person to sleep.

Intraoperative analgesia which is usually an opioid.

Intubation/assisted ventilation if muscle paralysis.

Reversal of muscle paralysis and recovery.

Post-operative analgesia.

Provide medication for post-operative nausea and vomiting.

Question 5

Give example of gases-volatiles-delivered via lungs.

(Inhalation)

Answer 5

N2O

Halothane

Fluroxene

Methoxyflurane

Enflurane

Isoflurane

Xenon

Question 6

Give examples of intravenous anaesthesia.

Answer 6

Propofol

Barbiturates

Etomidate

Ketamine

Question 7

Explain Guedel’s signs.

(Stages 1-4)

Answer 7

1 - Analgesia and still conscious

2 - Patient is unconcious and breathing has become erratic. This is an excitement phase where muscle tone can increase.

3 - Surgical anaesthesia with four levels describing increasing depth until breathing is weak. This is where you want to the patient to be in.

4 - Respiratory paralysis and possible/imminent death (not where you want to go).

Question 8

What is anaesthesia a combination of?

Answer 8

Analgesia

Hypnosis (loss of consciousness)

Depression of spinal reflexes

Muscle relaxation

Question 9

How is volatiles drug potency measured?

Answer 9

By minimum alveolar concentration (MAC).

Question 10

Explain what MAC is.

Answer 10

It’s a measure of the anaesthetic concentration in the alveolus at which 50% of subjects fail to move to surgical stimulus.

It’s like EC50, Km etc…

Question 11

How does the alveolar concetration to spinal cord concentration relate at equilibrium?

Answer 11

They are equal.

Question 12

Give examples of MAC.

Answer 12

Mac

MAC-BAR

MACawake

Question 13

Give factors that affect induction as well as recovery.

Answer 13

Blood:Gas partition

Oil:Gas partition

Question 14

What does a low Blood:Gas partition value indicate?

Answer 14

Fast induction and recovery

Question 15

What does Oil:Gas partition determine?

Answer 15

Potency and slow accumulation due to partition into fat.

Question 16

Give factors affecting MAC.

Answer 16

Question 17

Why is Nitrous Oxide often given with volatiles?

Answer 17

Because it decrease MAC.

This means that less of a volatile agent is needed to achieve the same result.

Question 18

Why is it preferable that Nitrous oxide reduces MAC?

Answer 18

Because that means that you won’t have to give as much of the volatile agent and therefore reduced side-effects.

Question 19

Explain the role of GABA receptors in anaesthesia.

Answer 19

Since GABA is the major inhibitory transmitter you target the receptor and increase the Cl- conductance.

This potentiates GABA activity and leads to anxiolysis, sedation, and anaesthesia.

Question 20

Give exception of anaesthesia not acting to potentiate GABA activity.

Answer 20

Xenon

N2O (Nitrous oxide)

Ketamine

Question 21

What do xenon, nitrous oxide and ketamine act on instead?

Answer 21

They interact with NMDA receptors instead and inhibit glutamate activity.

Question 22

Explain the effects of anaesthesia on the brain circuitry.

Answer 22

The connectivity between the reticular formation and cortex is lost.

The thalamus is inhibited.

Hippocampus is depressed leading to no memory.

Brainstem is depressed (can affect resp and CVS)

Spinal cord and depression of the dorsal horn. This leads to analgesia (suppression of pain)

Question 23

When are IV anaesthetics used?

Answer 23

As induction

Can also be given as sole anaesthetic in TIVA (Total Intravenous Anaesthesia)

Question 24

How does the target sites and system targets differ between volatiles and IV?

Answer 24

Same target sites and same system targets.

Ketamine however inhibits NMDA

Question 25

How do we describe IV anaesthetic potency?

Answer 25

Plasma concentration to achieve a specific end point

TIVA uses a defined PK based algorithm.

Question 26

In simple terms how does mixed anaesthesia work.

Answer 26

Bolus of IV anaesthesia to end point then switch to volatile.

Question 27

Causes to give local and regional anaesthesia.

Answer 27

Dentistry

Obstetrics

Regional surgery where the patient is awake

Post-op

Chronic pain management

Question 28

Give examples of local anaesthetics.

Answer 28

Lidocaine

Bupivacaine

Ropivacaine

Procaine

Question 29

Characteristics of local anaesthetics.

Answer 29

Lipid solubility - higher lipid solubility = more potent

pKa - lower pKa = faster onset

Protein binding - refers to duration

Question 30

Briefly explain how local anaesthetics work.

Answer 30

Prevent depolarisation by blocking sodium channels.

Question 31

Side effects of general anaesthesia.

Answer 31

Post-operative nausea and vomiting

CVS and hypotension specifically

Post-operative cognitive dysfunction

Chest infection

Allergic reactions and anaphylaxis