General anaesthetics

Question 1

General anaesthesia purpose

Answer 1

1. Loss of consciousness
2. Analgesia
3. Muscle relaxation (associated with a loss of reflexes).

Question 2

Stages of analgesia

Answer 2

Stage 1: analgesia (misnomer)
•	Drowsiness
Stage 2: Excitement
•	Loss of consciousness
Stage 3: Surgical aneasthesis
•	Regular respiration
•	Decline in muscle tone
•	Loss of reflexes
Stage 4: Medullary paralysis

Question 3

Give examples of injection/intravenous anaesthetics

Answer 3

1. Thiopental
2. Propofol
3. Etomidate
4. Midazolam (benzodiazepine)
5. Ketamine (dissociative anaesthetics)

Question 4

Effect on GABAa receptor function

Answer 4

Enhance GABAa receptor function

1. Volatile anaesthetics – bind at the interface between alpha and beta subunits
2. Intravenous anaesthetics – bind to beta subunits

Question 5

Effect on potassium channels, and the type of general anaesthetics that do this

Answer 5

Volatile and gaseous anaesthetics Activate potassium channels

Question 6

Effect on NMDA receptors and the type of general anaesthetics that do this

Answer 6

The following block NMDA receptors
Ketamine
Nitrous oxide

Question 7

Effect of GAs on other channels

Answer 7

Inhibit voltage – sensitive Ca2+ channels
Inhibit voltage-sensitive sodium channels
Inhibit Glycine, nicotinic and 5-HT ligand gated ion channels

Question 8

Overall Effect of general anaesthetics on the nervous system (i.e neurotransmitter release and excitability)

Answer 8

Inhibit excitatory synaptic transmission:

a. Decreases neurotransmitter release (presynaptic)
b. Decrease action of neurotransmitter (postsynaptic)
c. Decrease excitability of postsynaptic neurones

Question 9

Advantages of injectable anaesthetics

Answer 9

Easy to administer

Rapid induction

Question 10

Disadvantages of injectable anaesthetics

Answer 10

Complex pharmokinetics
Slow elimination
Side effects

Question 11

Give examples of dissociative anaesthetics

Answer 11

Ketamine

Tiletamine (phencyclidine)

Question 12

What is the action of ketamine?

Answer 12

NMDA channel blocker

Question 13

What are the advantages of dissociative anaesthetics

Answer 13

No cardiovascular or respiratory depression
Non-cumulative effects
Analgesic
High therapeutic index

Question 14

What are the disadvantages of dissociative anaesthetics

Answer 14

Psychic disturbances

Involuntary movements

Question 15

What are the Inhalation Anaesthetics?

Answer 15

Gas:
-NO2

Volatile liquids:

• Halothane – rarely used, metabolised to toxic metabolite
• Enflurane – may cause convulsions
• Isoflurane
• Desflurane/sevoflurane – rapid induction
• Methoxyflurane

Question 16

What are the Inhalation Anaesthetics useful for

Answer 16

Maintaining surgical anaesthetics

Question 17

Route of entry of Inhalation Anaesthetics

Answer 17

Lungs, so problem if these ar diseased

Question 18

Inhalation Anaesthetics process of entry/ mechanism

Answer 18

Small lipid soluble molecule, easily cross alveolar membrane.
Absorbed and excreted unchanged from lungs

Question 19

The differences in each Inhalation Anaesthetics arises from?

Answer 19

Solubility of different agents in blood and fat

Question 20

Chemical properties governing the speed of induction

Answer 20

Blood:gas partition coefficient (solubility in blood)
Oil:gas partition coefficient (solubility in fat)

Question 21

Physiological factors governing the speed of induction

Answer 21

Alveolar ventilation rate

Cardiac output

Question 22

How the Loading Dose governs the speed of induction in inhalation anaesthetics

Answer 22

Increasing initial concentration of agent in inspired air will increase rate of onset