General Anaesthetics

Question 1

Triad of General Anaesthesia

Answer 1

Unconsciousness
Analgesia
Muscle relaxation

Question 2

Stage 1 of anaesthetics

Answer 2

Analgesia
Conscious, drowsy, antinociception, amnesia, some lack of sensation.
Used for minor operations and labour

Question 3

Stage 2 of Anaesthesia

Answer 3

Excitement
Loss of consciousness but delirium, irregular cardiorespiration, apnea, spasticity, gagging, vomiting
Very unpleasant, aim to move through as quickly as possible

Question 4

Stage 3 of Anaethesia

Answer 4

Anaesthesia
Regular respiration, loss of reflex and muscle tone
General anaesthesia
Good for major surgery

Question 5

Stage 4 of Anaesthesia

Answer 5

Medullary paralysis
Depression of cardiorespiration, death

Question 6

N20

Answer 6

Keeps you in stage 1

Question 7

Properties of an ideal general anaesthetic

Answer 7

• stable
• potent
• non-toxic
• controllable
• rapid on (to get through stage 2) and rapid off (to control stage 3)
• adjustable (to maintain good level quickly to avoid harm to patient)
• minimal cardio-depressant
• minimal respiratory depressant
• non-irritant

Question 8

Inhalation anaesthetics

Answer 8

Controllable because gas exchange of lungs is rapid
Rapid blood-gas exchange
Usually halogenated ethers or hydrocarbons

Question 9

Intravenous anaesthetics

Answer 9

Injections
Very rapid, but short acting
Often used to put patient under, then gaseous used to keep them under

Question 10

Combined use of anaesthetics

Answer 10

• Pre-op - Midazolam and other benzodiazepines.
• Rapid unconsciousness. - I.V. rapid agent e.g. thiopental
• Maintain unconsciousness - inhalation agents e.g. N2O and Halothane
• Supplement analgesia - I.V. e.g. fentanyl.
• Paralysis. - neuromuscular block e.g. suxamethonium.

Question 11

Common inhalation anaesthetics

Answer 11

N2O - rapid, low potency, used in combination, obstetrics, analgesic
Volatile halogenated hydrocarbons - Widely used but some side effects especially cardiovascular & nausea

Question 12

Local anaesthetics block … which blocks local pain receptors

Answer 12

Voltage-gated sodium channels

Question 13

Do general anaesthetics work on CNS or PNS?

Answer 13

CNS
Two leading theories as to why

Question 14

Lipid theory of anaesthetic action

Answer 14

Neuronal function is due to membrane spanning proteins,
Lipophilic agents can soak into the lipid bilayer and affect the function of these ion channels
So lipophilic anaesthetics can interfere with the proteins

Question 15

Protein theory of anaesthetic action

Answer 15

Luciferase inhibition correlates with anaesthetic potency
Anaesthetics interact with membrane proteins, receptors and ligand gated ion channels

Question 16

GAs _ inhibitory receptors

Answer 16

Potentiate
Increase depolarisation
Make peaks deeper

Question 17

GAs _ excitatory receptors

Answer 17

Block

Question 18

GA effect at Na+ ion channels

Answer 18

Decreases the frequency of action and the chance of activation

Question 19

GAs effect on K+ ion channels

Answer 19

Increases the frequency of action and the hyperpolarisation