General Anaesthetics

Question 1

Therapeutic Index of general anaesthetics

Answer 1

~4

Question 2

Stages of anaesthesia

Answer 2

1- analgesia(some are hyperalgesic but not felt if unconscious)
2- Excitement/delirium (e.g. ethanol), try to skip this
3- Surgical anaesthesia (ethanol goes through this rapidly)
4- Respiratory paralysis/death/brainstem depression

Question 3

Types of anaesthetics

Answer 3

Inhalation - gases or volatile liquids

IV- developed for induction of anaesthesia, and short ops

Question 4

Factors increasing anaesthetic potency

Answer 4

unsaturation
ether groups
halogen substitution
LACK of hydrophilic groups as these reduce potency

Question 5

MOA theories for general anaesthetics

Answer 5

Initially thought MOA was through entering bilayer and disrupting but now thought that they bind to area of protein to inhibit function
Shown to inhibit glutamate + enhance GABA receptors

Question 6

Ketamine, NO and xenon MOA

Answer 6

Non-competitive NMDA antagonists

Question 7

Inhalation anaesthetics currently used

Answer 7

Halothane
Enflurane
Isoflurane
NO

Question 8

Measuring potency of inhalation anaesthetics

Answer 8

MAC- minimum alveolar conc needed to prevent movement in response to pain in 50% of subjects

Question 9

Factors affecting onset and recovery from anaesthetic

Answer 9

Poor blood solubility means more is gaseous so faster equilibrium in alveoli and brain, so quicker onset/offset
High fat solubility means slower recovery as stays in poorly perfused fatty areas for longer

Question 10

Ideal clinical anaesthetic properties

Answer 10

low MAC, low blood solubility

Question 11

NO ±

Answer 11

Not potent enough to be used as sole anaesthetic but helps reduce conc of other gas needed as a non-flammable carrier
Useful analgesic (childbirth/RTA)

Question 12

Isofluorane ±

Answer 12

Most widely used
More soluble in blood than servoflurane/enflurane so recovery/onset slower
SE: dose-related hypotension by dec SVR

Question 13

Sevofluorane advantages

Answer 13

very insoluble in blood so rapid onset/offset but this may mean post-op analgesic needed quickly
Pleasant to breathe so good for kids

Question 14

Enflurane ±

Answer 14

Less metabolised than halothane, unlikely to be hepatotoxic

SE: may cause twitching/seizure activity so not used much now

Question 15

Desflurane ±

Answer 15

less potent isoflurane with lower blood solubility

More needs to be given so can cause RT irritation

Question 16

Halothane ±

Answer 16

Potent, easy to breathe and non-irritant

A lot biotransformed by the liver so may be hepatotoxic, so not used much anymore

Question 17

Premedication purpose and drugs

Answer 17

Reduce anxiety/pain (opioids (fentanyl)/NSAIDs (diclofenac)/temazapam)
Prevent parasympathetic effects e.g. bradycardia (anti-muscarinics e.g. hyoscine)

Question 18

Postop medications

Answer 18

Anti-emetics e.g. droperidol (dopamine antagonist)

Question 19

Propofol±

Answer 19

Most commonly used, fast onset/offset and can be given during op slowly

Question 20

Thiopental±

Answer 20

Highly lipid soluble so dissolves in brain tissues quickly

Wears off quickly but still stored in fat

Question 21

Etomidate±

Answer 21

Fast onset and recovery

Excitement during induction, increased nausea and adrenocortical suppression so not used much anymore

Question 22

Ketamine±

Answer 22

IV or IM, good analgesic with lethal OD rare
Dissociative anaesthetic so can have patient awake but not feeling pain
Hallucinations in adults but used in children

Question 23

Intravenous anaesthetics

Answer 23

Propofol
Thipnetal
Etomidate
Ketamine

Question 24

Epidural use

Answer 24

Local anaesthetic e.g. bupivacaine (long duration) ± opioid painkiller, gives pain control below site of epidural
Used in childbirth, minor surgery, surgery when co-operation needed, post-op pain control