Principles of general anaesthesia Flashcards
What is important to remember about general anaesthetics
Although they are very useful drugs. they are also very dangerous and you have to be very skilled to use them
- 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 (important- don’t necessarily have pain relief if you are unconscious or immobile)
Muscle relaxation (important for surgery- to get through muscle mass).
Amnesia
At what concentrations of local anaesthetics do you get:
a) loss of consciousness
b) Suppression of reflex responses
Loss of consciousness at low concn
Suppression of reflex responses at high concn
So you get loss of consciousness first.
NB G.A.s vary greatly in their ability to induce analgesia, muscle relaxation and amnesia.
Summarise the history of general anaesthesia
Crawford Long (1842) —- CH3-CH2-O-CH2-CH3 (ether)
Horace Wells (20th Jan, 1845) — N N O (nitrous oxide)
William Morton & Charles Jackson —- CH3-CH2-O-CH2-CH3 (ether)
(16th Oct, 1846)
What are the two broad types of general anaesthetics
Gaseous/Inhalational
Intravenous
Describe the structural relationship between the different anaesthetic agents
They are all dissimilar!
Extraordinary chemical diversity ranging from simple chemically inert gases to complex barbiturates
List the inhalational general anaesthetics
Nitrous Oxide
Diethyl Ether
Halothane
Enflurane
List the intravenous general anaesthetics
Propofol
Etomidate
How can we define what is meant by general anaesthesia
Only one defining feature for all general anaesthetics;
‘Induce a loss of consciousness at low concentrations’
Additionally;
‘Induce an increasing lack of responsiveness at higher concentrations’
Describe the general structural differentiation between I.V and general anaesthetics
o IV generally contain rings.
o Inhalational GAs generally have halogens.
What was an early theory for the mechanism of action of general anaesthetics
Meyer/Overton
Correlation
Anaesthetic potency increases
in direct proportion with oil/water
partition coefficient
That is the more lipid soluble the drug- the more potent it was. Therefore, the site of action for general anaesthetics must have been in disrupting lipid bilayers.
Describe the problems that arised regarding the Meyer/Overton correlation
Problems: At relevant anaesthetic concns, change in bilayer was minute 2. How would this change impact membrane proteins?- which are involved in transmitting action potentials.
Describe the two real mechanisms for how general anaesthetics work
Reduced neuronal excitability or
Altered synaptic function (i.e effect on neurotransmitter release).
What are GABAa receptors
Most abundant, fast inhibitory, ligand-gated ion channels in the CNS
Different GABA channels are composed of different subunits- binding of different general anesthetics to different subunits effects the pharmacodynamics of the drug.
What do intravenous general anaesthetics target
GABAA
receptors
Bind to and potentiate their action to enhance GABA transmission.
Describe the subunits of the GABAa receptor that etomidate targets and the different effects produced
B3- suppression of spinal responses
A5- amnesia.