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PR3136 CA1 > L7 General Anesthetics > Flashcards

L7 General Anesthetics Flashcards

1
Q

Why is food and drinks permitted before surgery?

A

All sensory and autonomic reflexes must be inhibited

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2
Q

What properties should an ideal anaesthetic drug have? (8)

A
  • unconsciousness
  • analgesia: not responding to pain
  • muscle relaxation, to the point of paralysis
  • amnesia, around the procedure
  • brief and pleasant
  • depth of anaesthesia can be raised or lowered with ease
  • minimal adverse effects
  • margin of safety, large
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3
Q

Why are INH and IV anaesthetics used in combination for GA?

A

Synergistic: to ensure that induction is smooth and rapid, and that analgesia and muscle relaxation are adequate

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4
Q

Which inhalant GA gets into brain more quickly? nitrous oxide or halothane

A

nitrous oxide -> onset depends on distribution

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5
Q

Examaples of volatile liquids that are inhalant GA

A

halothene, desflurane, enflurane, isoflurane, sevoflurane

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6
Q

Examples of gases that are inhalant GA

A

nitrous oxide

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7
Q

What is MAC?

A

Minimum Alveolar Concentration, minimum concentration of drug in the alveolar air that will produce immobility in 50% of patients exposed to a painful stimuli

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8
Q

Volatile liquids GA are administered using ?

A

agent specific-vaporiser

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9
Q

Which of the volatile liquids inhalant GA is hepatotoxic?

A

halothane

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10
Q

Which of the metabolites of volatile liquids inhalant GA is nephrotoxic?

A

inorganic fluorides of isoflurane, sevoflurane and enflurane

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11
Q

Is halothane-associated hepatitis reversible?

A

Yes, once halothane is completely eliminated

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12
Q

Halothane MOA

A
  • little or no analgesia until unconsciousness supervenes

- relaxes skeletal muscle and potentiates skeletal muscle relaxants

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13
Q

What is a dose-dependent side effect of halothane?

A

Respiratory depression

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14
Q

Possible ADR of halothane

A

Decreases bp due to depression of cardiac output

- bradycardia and arrhythmia may also occur leading to hypotension and dysrhythmia

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15
Q

What is the MAC of halothane?

A

0.75%

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16
Q

What is the MAC of isoflurane?

A

1.4%

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17
Q

What is the MAC of sevoflurane?

A

2%

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18
Q

What is a distinct feature of isoflurane?

A

pungent smell

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19
Q

How does isoflurane decreases bp?

A

decrease in systemic vascular resistance

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20
Q

Which of the volatile liquid inhalant GA halothane/isoflurane/sevoflurane has the most rapid rate of osnet and recovery?

A

sevoflurane, lower blood solubility

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21
Q

When is sevoflurane unstable?

A

when exposed to CO2 in anaesthetic machines

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22
Q

What is the major concern of nitrous oxide?

A

postoperative nausea and vomiting

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23
Q

Is nitrous oxide commonly used as an adjunct or monotherapy?

A

Both!

  • adjunct: supplement the analgesic effects of primary anaesthetics
  • mono: analgesic agent eg dentistry, during labour
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24
Q

Examples of IV GA

A

thiopentone, etomidate, propofol, ketamine, midazolam

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25
Q

What are the 2 advantages of inhaled + IV anaesthetics?

A
  1. permit dosage of the inhalation agent to be reduced

2. produce effects (analgesia, anxiolysis) that cannot be achieved with an inhalation dose

26
Q

What is the duration of action of thiopentone when injected alone as a single dose?

A

Without inhaled agents, patient wakes up in 10 minutes

- hence, difficult to use IV GA only, require high dose

27
Q

What is the duration of action of thiopentone when injected alone as multiple doses/ infusion?

A

Depends on clearance

28
Q

What is the MOA of thiopentone?

A

Cause CNS depression by potentiating the action of the neurotransmitter GABA on GABAa receptor-gated chloride ion channels (binds to a positive regulatory allosteric site, allows receptor to bind better to GABA, usual amount of GABA)

29
Q

Which drug, thiopentone/propofol, has a more rapid recovery?

A

Propofol, patients move sooner and feel better

30
Q

What is the most common IV anaesthetic used in SG?

A

Propofol: ready-made in injectable form, no need to re-constitute (unlike thiopentone)

31
Q

Is propofol used for induction or maintenance?

A

Both!

32
Q

What is the time of onset and duration of action for propofol?

A

Unconsciousness develops within 60 seconds, short duration of action of approx 3-5min following single injection

33
Q

What is propofol extensively used for?

A

‘Day surgery’

- needs continuous, low-dose infusion for extended effects

34
Q

What is a huge advantange of using propofol over nitrous oxide?

A

Propofol has significantly reduced postoperative vomiting, may be related to an anti-ematic action

35
Q

What is a significant ADR from use of propofol?

A

Significant cardiovascular effect during induction (decrease bp and negative inotropic) -> hypotension

36
Q

CI of propofol (or used with caution)

A

Elderly patients, patients with compromised cardiac function, hypovolemic patients

37
Q

Does ketamine result in unconsciousness?

A

No, dissociative anaesthesia (feels dissociated from environment but still some awareness) and responsiveness to pain is lost

38
Q

What is the only IV anaesthetic that possess analgesic property?

A

Ketamine, hence very popular in third world countries as the only anaesthetic, due to lack of other anaesthetic agents

39
Q

Why is ketamine suitable for continuous infusion, without lengthening in duration of action?

A

Large Vd, rapid clearance

40
Q

ADR of ketamine, when does it usually happen and how it can be reduced?

A

Unpleasant psychologic reactions (hallucination, disturbing dreams, delirium) may occur during recovery from ketamine
- risk of psychologic adverse reactions may be reduced with premedication of diazepam or midazolam

41
Q

Anaesthetic adjuncts (4)

A

benzodiazepines, a2 adrenergic agonists, analgesics, neuromuscular blocking agents

42
Q

What are the uses of benzodiazepine: midazolam (IV)?

A
  • used for anxiolytics, amnesia and sedation prior to induction of anaesthesia (perioperative period)
  • or used for sedation during procedures not requiring GA eg. endoscopy
43
Q

Rank the IV GA according to CV and respiratory depressing effects

A

midazolam

44
Q

Midazolam SE is compounded by

A

concurrent usage of other agents

45
Q

How to minimise ADR of midazolam?

A

By injecting midazolam slowly (over 2 or more mins) and by waiting another 2 min for full effects to devleop before dosing again if req

46
Q

How is midazolam metabolised in elderly patients?

A

In liver, but more sensitive and slower recovery

47
Q

Can dexmedetomide be used as a GA?

A

No, sedation and analgesic effects only, does not produce reliable GA even at maximal dose, used as adjunct

48
Q

Duration of action of dexmedetomide?

A

short term sedation, <24hr

49
Q

Dexemedetomidine

A

highly selective a2 adrenergic receptor agonsist

50
Q

What are some undesirable side effects of dexmedetomidine?

A

nausea, dry mouth, hypotension, bradycardia

51
Q

Relative potency to morphine and duration of action - sufentanil

A

1000x, intermediate 15min

52
Q

Relative potency to morphine and duration of action - remifentanil

A

300x, ultra-short 10min

53
Q

Relative potency to morphine and duration of action - fentanyl

A

80x, intermediate 30min

54
Q

Relative potency to morphine and duration of action - alfentanil

A

15x, intermediate 20min

55
Q

Neuromucular blockers - depolarising

A

succinylcholine

56
Q

Neuromucular blockers - non-depolarising

A

Vecuronium

57
Q

DDI with neuromuscular blockers

A

Barbiturates - will precipitate when mixed with muscle relaxants, should be allowed to clear from the IV line prior to injection of muscle relaxant

58
Q

When is neuromuscular blockers administered for anaesthesia?

A

Inducition, relax muscles of jaw, neck and airway - facilitate laryngoscopy and endotracheal intubation

59
Q

What is the principal adr of GA?

A

depression of respiratory and cardiac performance

60
Q

How are inhalation anaesthetics eliminated?

A

Through expired air

61
Q

How does nitrous oxide differ from other gas?

A
  • Very high MAC, cannot be used alone to produce GA

- High analgesic potency, frequently combined with other gas to supplement their analgesic effects

62
Q

Induction of anaesthesia usually accomplished with

A

short-acting barbiturates eg thiopentone

PR3136 CA1 (8 decks)

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