General anaesthesia Flashcards
What traits do all general anaesthetises have?
They cause a loss of consciousness at low concentrations and suppression of reflex responses at high concentrations
What are the two main type s of GA
IV which generally contain rings and inhalation types with halogens
What is the meyer overton correlation theory of how anaesthesia works?
GAs penetrate the lipid bilayer and disrupt AP propagation
What is evidence for the meyer overton correlation
Anaesthetic potency increases as lipid solubility increases
What is evidence against the meyer overton correlation
At relevant concentrations, changes in the bilyar was minute and no changes in lipid bilayer proteins can be seen - this would be changed if GAs disrupted AP propagation
What is the molecular target theory of the MoA of GAs
they have either or both effects:
- altered synaptic function
- reduced neuronal excitability
How do IV agents alter synaptic function according to the molecular target MoA theory
enhance the GABA a receptor and enhance GABA transmission, leading to subunits targeted:
beta3 - suppression of reflex responses and expressed in spinal cord
alpha 5 - amnesia - expressed in hippocampus/amygdala
What is the difference between altered synaptic function in IV compared to inhalation agents in the molecular target theory
In inhalation agents, it is a less powerful and less selective effect.
How do halogen inhalation agents alter synaptic function according to the molecular target MoA theory
- target GABA a/glycine receptors - alpha1 causes a suppression of reflex responses
- decrease firing rate of neuronal NAChR
How do non-halogen inhalation agents (aka nitrous oxide) alter synaptic function according to the molecular target MoA theory
- block NMDA type glutamate receptors - compete with co-agonist glycine
How do halogen inhalation agents reduce neuronal excitability according to the molecular target MoA theory
enhance background leak of K channels to cause hyperpolarisation of cells - TREK (background leak) of K+ channels
Compare the selectivity and potency of IV and inhaled GAs
IV GAs are more selective and inhaled more non selective but they are equally as potent
What happens in a neuroanatomy standpoint when you lose conciousness due to GA
The thalamocortical neurones are depressed by the GA’s hyperpolarising them by activating TREK channels or potentiationg GABA Rs.
RAF neurones are also influenced
GAs also disrupt the communication between the RAF
How can GAs cause suppression of reflex responses
Due to at the dorsal horn, GABAa receptors are at a high density. It causes depression of the reflex pathways in the spinal cord
How can GAs cause amnesia?
Influences on the GABAa alpha5 subunits, causing a decrease in synaptic transmission in the hippocampus and amygdala
