Principles of General Anaesthesia

Question 1

2 common clinical effects of GA

Answer 1

• loss of consciousness at low conc

- suppress of reflex responses at high conc

Question 2

What are the different types of GA?

Answer 2

inhalation
e.g NO, Diethyl Ether, Halothane, Enflurane

Intravenous
e.g Propofol, Etomidate

Question 3

Describe the MoA of GA

Answer 3

-

Question 4

• more lipid soluble they are, the better/worse anesthetic agents they are

Answer 4

• more lipid soluble they are, the better anesthetic agents they are

Question 5

Describe the MoA of GA

a) IV Agents
b) Inhalation agents
c) Nitrous Oxide

Answer 5

a) IV agents –> target GABAa Receptors

• they enhance GABA a receptor function
• enhance inhibitory effects of GABA
• -> suppression of reflex responses (via receptors w B3 subunits)
• -> amnesia (via receptors w a5 subunits)

b) Inhalation agents - also acts on GABAa receptors / Glycine receptors
- less selective

–> suppression of reflex responses (via receptors w a1 subunits)

c) NO –> blocks NMDA type glutamate receptors
- -> compete w co agonist glycine

Question 6

Increase dose of drug –> activity

Answer 6

???

Question 7

Inhalation agent can target:

Answer 7

• Neuronal nicotinic ACh receptors
• -> important as aan analgesic
• -> by altering synaptic function
• TREK (background leak) K+ channels
• -> important in maintaining regulating consciousness
• -> by reducing neuronal excitability

Question 8

How does loss of consciousness come about?

Answer 8

• there is depression in excitability of thalamocortical neurons
• -> by influencing reticular activating neurons

–> GABA + Background K+ leak channels = important in mediating loss of consciousness

Question 9

How does suppression of reflex responses come about?

Answer 9

• GA depresses reflex pathways in the spinal cord

Question 10

How does amnesic effect come about?

Answer 10

• GA decreases synaptic transmission in hippocampus/amygdala

Question 11

difference between inhalation and intravenous GA

Answer 11

IV –> straight to blood –> fast access to brain

Inhale –> lungs –> goes to blood –> go to brain

important = blood:gas partition coefficient

low bgpc = most drug will dissolve in blood poorly- some drug will dissolves but largely will remain in gas format

if anesthetic has low bgpc –> drug goes to lung to brain more quickly (good level of anesthetic effects)

High bgpc = most drug will dissolve well in blood

• slower transfer of anesthetic agent going from lung –> the brain
• -> difficult to control

Question 12

NOTE

Low bgpc = allows quick / good control of anaesthesia

Answer 12

-

Question 13

NOTE

IV= used to induce anaesthesia (e.g propofol)
–> inhalation agent is then used to control

Answer 13

-

Question 14

compare between inhalation and intravenous anesthetics

Answer 14

inhalation anaesthetics

• rapidly eliminated
• allows rapid control of depth of anaesthesia

Intravenous anaesthetics
- Fast induction
- Less coughing/
depth of anaesthesia excitatory phenomena

Question 15

disadvantage of antes

Answer 15

• more likely to get excitatory phenomena

- increase coughing

Question 16

What are some other drugs that you might use to induce

a) analgesia
b) muscle relaxation
c) Amnesia

Answer 16

What are some other drugs that you might use to induce

a) analgesia
- -> Opioid

b) muscle relaxation
- -> NM Blocking drugs

c) Amnesia
- -> Benzodiazepines

Question 17

anesthetics = VERY LIPID SOLUBLE

–>

Answer 17

• high complication for obese patients