Principles of General Anaesthesia Flashcards

1
Q

What are the five clinically desirable effects of general anaesthetics? State which two effects are caused by ALL general anaesthetics.

A
Loss of consciousness (ALL) 
Suppression of reflex responses (ALL) 
Relief of pain (analgesia)
Muscle relaxation  
Amnesia
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2
Q

Name 4 inhalational general anaesthetics.

A

Nitric oxide
Diethyl ether
Halothane
Enflurane

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3
Q

Name 2 IV general anaesthetics.

A

Propofol

Etomidate

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4
Q

What is the Meyer/Overton correlation?

A

Anesthetic potency directly correlated with lipid solubility (oil/water partition coefficient)

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5
Q

What was the explanation for the Meyer/Overton correlation?

A

The drugs disturbed the lipid bilayer

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6
Q

What were the problems with the Meyer/Overton explanation?

A

At therapeutic doses, changes to the lipid bilayer were minute
How would the change impact on membrane proteins?

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7
Q

What are the two real mechanisms of action of general anaesthetics?

A

Reduced neuronal excitability

Altered synaptic function

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8
Q

Describe the difference in the selectivity of IV and inhalational agents.

A

IV agents are more selective for GABA-A

Inhalational agents are far less selective

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9
Q

Which specific subunits of the GABA-A receptor do IV agents that alter synaptic function target and what are their effects?

A

Beta 3: important in suppression of reflex responses

Alpha 5: important in amnesia

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10
Q

What are the two main targets of inhalational agents that alter synaptic function?

A

GABA-A receptors (mainly in brain)
Glycine receptors (mainly in spinal cord)
(increase inhibitory activity of both)

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11
Q

Which subunit of the GABA-A receptor do inhalational agents seem to be more selective for?

A

Alpha 1: important in suppression of reflex responses

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12
Q

Explain how nitrous oxide induces its anaesthetic effect.

A

NO competes for + blocks the glycine-binding site on NMDA receptors (glutamate receptors)
Glycine is an important coagonist of NMDA receptors (it allows the full receptor response to be transduced)

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13
Q

What is the effect of blocking neuronal nicotinic acetylcholinereceptors with regards to general anaesthesia?

A

Blocking nAChR leads to reduced nerve conduction

Important for analgesic effect

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14
Q

Which channels are important in reducing neuronal excitability via the action of inhalational agents? What effect is associated with this?

A

TREK (background leaky K+ channels)
Opening TREK leads to hyperpolarisation of neurones + reduced excitability
Loss of consciousness

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15
Q

Inhalational agents are less selective than IV agents. What effect does this have on the dose needed to induce general anaesthesia?

A

Generally, a higher dose of inhalational agents is required

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16
Q

Explain how general anaesthetics cause a loss of consciousness.

A

Loss of consciousness is caused by depressing the excitability of thalamocortical neurones + reticular activating system neurones
Mediated by TREK channels + GABA-A receptors
Tricks brain that there is lack of sensory stimulus

17
Q

Explain how general anaesthetics suppress reflex responses.

A

Depression of reflex pathways in the dorsal horn of the spinal cord
By anaesthetics that enhance GABA-A + glycine function

18
Q

Explain how general anaesthetics cause amnesia.

A

Many GABA-A receptors in the hippocampus with alpha 5 subunit
GA’s stimulate these receptors to decrease synaptic transmission in the hippocampus

19
Q

Explain how blood: gas partition coefficient affects the speed at which the general anaesthetic penetrates the brain.

A

If GA dissolves readily in blood, there is less GA in the gas phase in blood + hence less penetrates the BBB to reach the brain
Only anaesthetic in the gas phase diffuses easily into the brain

20
Q

Would a general anaesthetics with a high or low blood: gas partition coefficient be useful for anaesthetics and why?

A

LOW
Less GA dissolves in the blood so more is left in the gas phase
Hence more of the drug will penetrate the BBB + reach the brain

21
Q

What are the benefits of inhalation anaesthetics?

A

Rapidly eliminated

Good control of the depth of anaesthesia

22
Q

What are the benefits of IV anaesthetics?

A

Fast induction

Less coughing/ excitatory phenomena

23
Q

What types of drugs can be used alongside general anaesthetics to achieve:

a. Relief of pain
b. Muscle relaxation
c. Amnesia

A

Relief of pain: Opioids
Muscle relaxation: Neuromuscular blockers
Amnesia: Benzodiazepines

24
Q

How are general anaesthetics often administered in a clinical setting?

A

Induce LOC + suppression of reflexes with Propofol (IV)

Maintain effects with Enflurane (Inh.)