principles of general anaesthesia

Question 1

what is general anaesthesia?

Answer 1

Loss of consciousness (at low concentrations)
Suppression of reflex responses (at high concentrations)
Relief of pain (analgesia)
Muscle relaxation
Amnesia

Question 2

what are the 2 classes of general anaesthetics? and give examples of each

Answer 2

gaseous/ inhalation
eg. nitrous oxide, diethyl ether, halothane, enflurane

intravenous
eg. propofol, etomidate

Question 3

what is the current theory of the mechamism of action of general anaesthetics?

Answer 3

Reduced neuronal excitability or

Altered synaptic function

Question 4

what is the MOA of IV general anaesthetics

Answer 4

increase activity of GABAa receptors

beta3 subunits- Suppression of reflex responses

alpha5 subunits- amnesia

Question 5

what is the MOA of inhalation agents ?

Answer 5

act on GABAa receptors

glycine receptors also have an inhibitory role particularly in lower brainstem and spinal chord- possible target

Question 6

how does nitrous oxide work?

Answer 6

blocks NMDA-type glutamate receptors (block excitatory stimulation)

Question 7

where would the target for loss of consciousness be in the brain?

Answer 7

depress excitability of the thalamocortical neurons- hyperpolarize neurons by activating TREK channels (background leak channels) and or GABAa receptors

stops the RAS from picking up sensory inputs so will reduce consciousness

Question 8

where is the target for amnesia in the brain?

Answer 8

decrease synaptic transmission in the hippocampus/amygdala

Question 9

what are the pros and cons to inhalation and IV agents

Answer 9

IV- fast onset

- less coughing 
- but less control over recovery (relies on liver to metabolise)

inhalation- less quick onset

    - irritation can lead to cough reflex 
     - rapidly eliminated by breathing out 
   - good control of depth of anaesthesia