General Anaesthetics

Question 1

Describe the structure of a nerve

Answer 1

Bundle of neurone axons surrounded by epineurium

Question 2

What is anaesthesia?

Answer 2

Reversible loss of awareness of pain

Question 3

What is the difference between local, regional and general anaesthesia?

Answer 3

Local - Remains conscious, cheaper and safer
Regional - Larger area involved than local
General - Central effects, loss of consciousness

Question 4

What is stage 1 of anaesthesia?

Answer 4

Induction/analgesia
Conscious but drowsy
Reduced pain response

Question 5

What is stage 2 of anaesthesia?

Answer 5

Excitement
Loss of response to non-pain stimuli
Gag reflex, coughing

Question 6

Why does stage 2 anaesthesia have to be limited?

Answer 6

Choking
Breath holding
Talking
Vomiting
Movement

Question 7

What is stage 3 of anaesthesia?

Answer 7

Ideal stage for surgery
Regular respiration
Some reflexes
No movement
Shallow breathing

Question 8

What is stage 4 of anaesthesia?

Answer 8

Overdose
Medullary paralysis
Respiratory and vasomotor control ceases
Death

Question 9

What are the ideal anaesthetic pharmacokinetics?

Answer 9

Rapid induction and recovery
Avoid phase 2 and not reach stage 4
Avoid side effects

Question 10

Why are drugs used in combination for anaesthetics?

Answer 10

Stages become less apparent

Question 11

What is the advantage of fast induction and recovery?

Answer 11

Reduces stage 2
Maintains homeostatic reflexes
Patient usually amnesic

Question 12

What is the lipid theory for GA MoA?

Answer 12

Changing membrane protein conformation by changing environment they are dissolved in

Question 13

What are the protein theories for GA MoA?

Answer 13

Potentiated GABAa receptor function
Inhibition of NMDA receptor function
Potentiated two-pore potassium channel function

Question 14

What are the pros and cons of inhaled anaesthetics?

Answer 14

Easy to maintain degree of anaesthesia, rapid emergence

Complicated and expensive equipment, administered via mask, atmospheric pollution

Question 15

Why are scavenger systems required?

Answer 15

Fluranes generate fluoride which cause renal toxicity

Halothanes are converted to bromide and TFA which cause hepatotoxicity

Question 16

What is the blood-gas partition coefficient?

Answer 16

Measure of how well drug dissolves in blood
Determine rate of induction and recovery
Low blood solubility = faster recovery

Question 17

What is the oil-gas partition coefficient?

Answer 17

How well drug dissolves in fat, higher coefficient means more potent drug but more will dissolve in fat

Question 18

What is the disadvantage of a high oil-gas partition coefficient?

Answer 18

Anaesthetic takes long time to leave fat

Slow recovery - patient likely to be groggy

Question 19

What is likely to make the “hangover” phase of anaesthetics worse?

Answer 19

Higher body fat percentage

More fat soluble drug

Question 20

What are the most commonly used anaesthetics?

Answer 20

N2O and isoflurane

Question 21

Why are ethers not widely used?

Answer 21

Explosive, irritant and cause nausea

Question 22

What are the positives of isoflurane?

Answer 22

No metabolism
Little toxicity
Not proconvulsive

Question 23

What are the negatives of isoflurane?

Answer 23

Twice the price of halothane
Causes hypotension
Coronary vasodilator - may divert blood away from narrowed arteries
Worries surrounding neurodegeneration

Question 24

What are the positives of sevoflurane?

Answer 24

Rapid induction and recovery

Little metabolism

Question 25

What are the negatives of sevoflurane?

Answer 25

5x cost of halothane Neurodegeneration concerns Post-op analgesia required

Question 26

What are the positives of nitrous oxide?

Answer 26

Quick induction and recovery | Doesn't cause loss of consciousness - low potency

Question 27

What are the negatives of nitrous oxide?

Answer 27

Transient hypoxia due to dilution of oxygen in lungs | Extra O2 required at end of anaesthesia

Question 28

When is nitrous oxide contraindicated?

Answer 28

Early pregnancy Pernicious anaemia Scuba diving

Question 29

What are the advantages and disadvantages of IV anaesthetics?

Answer 29

Rapid induction, no stage 2, simple apparatus, pleasant induction, no atmospheric pollution Difficult to control levels of anaesthesia, slow recovery, finite duration but can give infusion, vein damage

Question 30

Describe the pharmacokinetics of thiopental

Answer 30

Lipophilic Induction perfusion rate limited Rapid distribution Slow distribution into fat

Question 31

What are the negatives of thiopental?

Answer 31

Long hangover Increases HR and cardiac oxygen demand Hypotension in hypovolaemic patients Can cause respiratory depression

Question 32

What are the advantages of propofol?

Answer 32

Rapidly metabolised so rapid recovery | Can be continually infused to maintain anaesthesia without inhaled agent

Question 33

How does propofol cause anaesthesia?

Answer 33

Potentiates GABAa receptors

Question 34

Describe the anaesthetic effect of ketamine

Answer 34

Causes analgesia and amnesia but patient is still partly conscious

Question 35

How does ketamine cause anaesthesia?

Answer 35

Non-competitive antagonist at NMDA receptors

Question 36

What are the positives of ketamine?

Answer 36

Safe for emergency situations | Little effect on respiration and BP

Question 37

What are the negatives of ketamine?

Answer 37

High abuse potential Increases HR Olney's lesions - neurotoxicity from NMDA receptor antagonist