Principles of general anaesthesia

Question 1

Recall 2 effects shared by all general anaesthetcis

Answer 1

Loss of consciousness and suppression of reflexes

Question 2

What are the 2 possible MOAs of general anaesthetics?

Answer 2

Altered synaptic function

Reduced neuronal excitability

Question 3

Describe how general anaesthetics can affect neuronal excitability

Answer 3

Only inhaled agents
Increase TREK channel opening
Hyperpolarisation of neurons suppresses the reflex responses

Question 4

What are TREK channels?

Answer 4

Background leak K+ channels

Question 5

By what mechanism do IV agents affect synaptic function?

Answer 5

Act on GABA-A receptors
Action on beta 3 subunit suppresses reflexes
Action on alpha 5 subunit causes amnesia

Question 6

Recall the receptors that are acted on by inhaled agents to alter synaptic function

Answer 6

GABA-A receptors
Glycine receptors
NMDA Glu receptors

Question 7

Compare the use of inhaled vs IV agents for alteration of synaptic function

Answer 7

IV agents much more selective for GABA-A Rs than inhaled so have a more powerful effect
Inhaled agents affect far more targets due to lower specificity

Question 8

Describe how inhaled agents tend to affect GABA receptors

Answer 8

Tend to be more selective for GABA receptors with an alpha 1 subunit which are present in the spinal cord and therefore suppress reflex action

Question 9

What sort of activity to glycine receptors show?

Answer 9

Inhibitory - they are homologous to GABA receptors

Question 10

Recall an example of an anaesthetic that has an effect on NMDA receptors

Answer 10

Inhaled nitrous oxide

Question 11

Recall the MOA of nitrous oxide as a general anaesthetic

Answer 11

Competitive inhibitor of NDA Glu receptor

Potently co-agonised by glycine

Question 12

Recall an example of an IC general anaesthetic

Answer 12

Propofol

Question 13

What are the main neuroanatomical sites involved in the loss of consciousness due to general anaesthetics?

Answer 13

Hypothalamocortical neurons

RAS

Question 14

Recall how depression of hypothalamocortical neurons is mediated by local anaesthetics

Answer 14

Inhibits TREK channels

Enhances GABA function

Question 15

How do general anaesthetics affect the RAS?

Answer 15

Suppress it to reduce its activating influence of hypothalamocortical neurons

Question 16

What is the main neuroanatomical site responsible for the suppression of reflexes by general anaesthesia?

Answer 16

Dorsal horn of spinal cord

Question 17

Recall the MOA of general anaesthetics in the dorsal horn of the spinal cord

Answer 17

Many GABA receptors present

Enhancement of GABA decreases activity of dorsal pathways

Question 18

What are the main neuroanatomical sites responsible for the induction of amnesia by general anaesthesia?

Answer 18

Hippocampus and amygdala

Question 19

Describe the MOA by which general anaesthetic induce amnesia

Answer 19

Hit Alpha 5 subunit of GABA receptors in the hippocampus and amygdala to decrease synaptic transmission

Question 20

Compare the methods of excretion of inhaled vs IV agents

Answer 20

Inhalation: via lungs - gives very good control due to ability to remove drug from lungs to alter blood:gas partition coefficient
IV: excretion dependent on hepatorenal function so gives fa less control

Question 21

How does blood gas partition coefficient affect blood solubility of the drug?

Answer 21

Low BGPC results in large proportion remaining in gaseous form, dissolving in blood and entering brain
High BGPS does opposite

Question 22

What is the normal pattern of use for IV and inhaled general anaesthetics?

Answer 22

IV for induction, inhaled agent to maintain

Question 23

What sort of agent is coadministered alongside a general anaesthetic to relieve pain?

Answer 23

Opiate

Question 24

What sort of agent is coadministered alongside a general anaesthetic to relax muscles?

Answer 24

NMJ blocker like suxamethonium