Principles of General Anaesthesia Flashcards
What are the five clinically desirable effects of general anaesthetics? State which two effects are caused by ALL general anaesthetics.
Loss of consciousness (ALL) Suppression of reflex responses (ALL) Relief of pain (analgesia) Muscle relaxation Amnesia
Name 4 inhalational general anaesthetics.
Nitric oxide
Diethyl ether
Halothane
Enflurane
Name 2 IV general anaesthetics.
Propofol
Etomidate
What is the Meyer/Overton correlation?
Anesthetic potency directly correlated with lipid solubility (oil/water partition coefficient)
What was the explanation for the Meyer/Overton correlation?
The drugs disturbed the lipid bilayer
What were the problems with the Meyer/Overton explanation?
At therapeutic doses, changes to the lipid bilayer were minute
How would the change impact on membrane proteins?
What are the two real mechanisms of action of general anaesthetics?
Reduced neuronal excitability
Altered synaptic function
Describe the difference in the selectivity of IV and inhalational agents.
IV agents are more selective for GABA-A
Inhalational agents are far less selective
Which specific subunits of the GABA-A receptor do IV agents that alter synaptic function target and what are their effects?
Beta 3: important in suppression of reflex responses
Alpha 5: important in amnesia
What are the two main targets of inhalational agents that alter synaptic function?
GABA-A receptors (mainly in brain)
Glycine receptors (mainly in spinal cord)
(increase inhibitory activity of both)
Which subunit of the GABA-A receptor do inhalational agents seem to be more selective for?
Alpha 1: important in suppression of reflex responses
Explain how nitrous oxide induces its anaesthetic effect.
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)
What is the effect of blocking neuronal nicotinic acetylcholinereceptors with regards to general anaesthesia?
Blocking nAChR leads to reduced nerve conduction
Important for analgesic effect
Which channels are important in reducing neuronal excitability via the action of inhalational agents? What effect is associated with this?
TREK (background leaky K+ channels)
Opening TREK leads to hyperpolarisation of neurones + reduced excitability
Loss of consciousness
Inhalational agents are less selective than IV agents. What effect does this have on the dose needed to induce general anaesthesia?
Generally, a higher dose of inhalational agents is required