Principles of General Anaesthesia Flashcards
what anaesthetic conc is required for loss of consciousness
Low
what anaesthetic conc is required for loss of reflex responses
High
2 criteria for general anaesthetics?
- Loss of consciousness
- Suppression of reflex responses
4 examples of inhalational GA?
- Nitrous oxide
- Diethyl Ether
- Halothane
- Enflurane
2 examples of IV GA?
- Propofol
- Etomidate
What is peculiar about the structures of GA
They are all different
How was the lipid solubility theory of GA proven wrong? (2)
- At relevant concentrations (clinical doses), the change in the lipid bilayer was minute
- How would this change impact membrane proteins?
MOA of IV GA?
- They alter synaptic function primarily though GABAA receptors (they potentiate and enhance GABA)
Suppression of reflexes MOA of IV GA?
- The ability of I.V. agents to suppress reflex responses seems to be due to their effect on GABA receptors that contain the beta3 subunit
The effect on GABA receptors that contain the beta3 subunit by IV GA causes…?
Suppression of reflex responses
Amnesia MOA of IV GA?
- The ability of I.V. agents to cause amnesia seems to be due to their effect on GABA receptors that contain the alpha5 subunit (lots of these in the hippocampus)
What do IV GA promote regarding polarisation of cells (think receptor they act on)
Hyperpolarisation
The effect on GABA receptors that contain the alpha5 subunit by IV GA causes …
Amnesia
MOA of inhalational GA (receptors they target, (5))
- They can have an effect on GABAA receptors
- glycine receptors Particularly important in spinal cord and lower brainstem – these contain alpha1 subunits – these are linked to suppression of reflexes
- nitrous oxide block NMDA-type glutamate receptors
- can also inhibit nicotinic ACh receptors
- Can also activate TREK K+ channels Important for consciousness
what receptor is important for consciousness (2)
TREK K+ channels
GABAa
TREK K+ channels are important for?
Consciousness
what receptor is important for suppression of reflexes
glycine receptors and GABAreceptors
what receptor is important for analgesia
nAchR and GABAa with the alpha5 subunit
nAchR are important for (regarding GA)?
Analgesia
glycine receptors are important for?
suppression of reflexes
Which is more selective, IV or gaseous GA
IV
Which 2 neurons are important for loss of consciousness
reticular activating neurons OR depression of excitability of thalamocortical neurons
How is an IV GA excreted?
Via metabolism in the liver/kidney etc
How is an inhalational GA excreted?
Out the lungs
What does rate of inhalational GA excretion depend on
blood/gas partition coefficient
Explain the blood/gas partition coefficient
- If the agent dissolves poorly in the blood (low partition coefficient), lots of it remains gaseous in the blood – this diffuses easily into the brain (this is good)
- If the agent dissolves well in the blood (high coefficient), it doesn’t easily enter the brain due to the BBB
- It is also easier to clear an agent with a low partition coefficient because it can diffuse out as easily as it moved in
Basically agents with a low blood:gas partition coefficient are favourable as it gives you more control over anaesthesia
Low blood:gas partition coefficient impact on entry to brain?
- If the agent dissolves poorly in the blood (low partition coefficient), lots of it remains gaseous in the blood – this diffuses easily into the brain (this is good)
Low blood:gas partition coefficient means how much dissolves?
Not much dissolves
High blood:gas partition coefficient impact on entry to brain?
If the agent dissolves well in the blood (high coefficient), it doesn’t easily enter the brain due to the BBB
High or low blood:gas partition coefficient is favourable for anaesthesia?
Low as it gives you more control over anaesthesia
Thinking control of the rates of excretion, what type of general anaesthetics are administered when during an op
an IV agent is used to induce anaesthesia, and then an inhalational agent to control the anaesthesia
Speed of elimination of inhalational general anaesthetics?
Quick
Speed of elimination of IV general anaesthetics?
Slow
Speed of effect of inhalational general anaesthetics?
Slow
Speed of effect of IV general anaesthetics?
Quick
Why do some people only use IV anaesthetics
because less coughing and inhalational can cause seizures
What type of GA do you want for suppression of reflexes and why
, you want an easy drug to control i.e. an inhalational anaesthetic
What needs to be taken into account when dealing with obese people and GA
Anaesthetics are extremely lipid soluble and so will sit in your adipose tissue, this can leak back into your blood as well. This needs to be taken into account when dealing with fatty boom battys.
