Principles of general anaesthesia Flashcards

1
Q

Recall 2 effects shared by all general anaesthetcis

A

Loss of consciousness and suppression of reflexes

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2
Q

What are the 2 possible MOAs of general anaesthetics?

A

Altered synaptic function

Reduced neuronal excitability

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3
Q

Describe how general anaesthetics can affect neuronal excitability

A

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

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4
Q

What are TREK channels?

A

Background leak K+ channels

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5
Q

By what mechanism do IV agents affect synaptic function?

A

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

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6
Q

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

A

GABA-A receptors
Glycine receptors
NMDA Glu receptors

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7
Q

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

A

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

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8
Q

Describe how inhaled agents tend to affect GABA receptors

A

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

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9
Q

What sort of activity to glycine receptors show?

A

Inhibitory - they are homologous to GABA receptors

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10
Q

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

A

Inhaled nitrous oxide

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11
Q

Recall the MOA of nitrous oxide as a general anaesthetic

A

Competitive inhibitor of NDA Glu receptor

Potently co-agonised by glycine

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12
Q

Recall an example of an IC general anaesthetic

A

Propofol

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13
Q

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

A

Hypothalamocortical neurons

RAS

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14
Q

Recall how depression of hypothalamocortical neurons is mediated by local anaesthetics

A

Inhibits TREK channels

Enhances GABA function

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15
Q

How do general anaesthetics affect the RAS?

A

Suppress it to reduce its activating influence of hypothalamocortical neurons

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16
Q

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

A

Dorsal horn of spinal cord

17
Q

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

A

Many GABA receptors present

Enhancement of GABA decreases activity of dorsal pathways

18
Q

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

A

Hippocampus and amygdala

19
Q

Describe the MOA by which general anaesthetic induce amnesia

A

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

20
Q

Compare the methods of excretion of inhaled vs IV agents

A

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

21
Q

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

A

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

22
Q

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

A

IV for induction, inhaled agent to maintain

23
Q

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

A

Opiate

24
Q

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

A

NMJ blocker like suxamethonium