Volatiles Flashcards

1
Q

What is the molecular weight of halothane?

A

197

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2
Q

What is the molecular weight of isoflurane?

A

184.5

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3
Q

What is the molecular weight of enflurane?

A

184.5

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4
Q

What is the molecular weight of desflurane?

A

168

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5
Q

What is the molecular weight of sevoflurane?

A

200.1

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6
Q

What is the molecular weight of nitrous oxide?

A

44

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7
Q

What is the molecular weight of xenon?

A

131

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8
Q

What is the boiling point of halothane?

A

50.2

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9
Q

What is the boiling point of isoflurane?

A

48.5

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10
Q

What is the boiling point of enflurane?

A

56.5

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11
Q

What is the boiling point of desflurane?

A

23.5

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12
Q

What is the boiling point of sevoflurane?

A

58.5

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13
Q

What is the boiling point of nitrous oxide?

A

-88

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14
Q

What is the boiling point of xenon?

A

-108

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15
Q

What is the SVP of halothane?

A

32.3

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16
Q

What is the SVP of isoflurane?

A

33.2

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17
Q

What is the SVP of enflurane?

A

23.3

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18
Q

What is the SVP of desflurane?

A

89.2

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19
Q

What is the SVP of sevoflurane?

A

22.7

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20
Q

What is the SVP of nitrous oxide?

A

5200

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21
Q

What is the SVP of xenon?

A

unknown

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22
Q

What is the MAC of halothane?

A

0.75

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23
Q

What is the MAC of isoflurane?

A

1.17

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24
Q

What is the MAC of enflurane?

A

1.68

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25
Q

What is the MAC of desflurane?

A

6.6

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26
Q

What is the MAC of sevoflurane?

A

1.8-2.2

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27
Q

What is the MAC of nitrous oxide?

A

105

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28
Q

What is the MAC of xenon?

A

71

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29
Q

What is the blood:gas partition coefficient of halothane?

A

2.4

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30
Q

What is the blood:gas partition coefficient of isoflurane?

A

1.4

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31
Q

What is the blood:gas partition coefficient of enflurane?

A

1.8

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32
Q

What is the blood:gas partition coefficient of desflurane?

A

0.42

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33
Q

What is the blood:gas partition coefficient of sevoflurane?

A

0.7

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34
Q

What is the blood:gas partition coefficient of nitrous oxide?

A

0.47

35
Q

What is the blood:gas partition coefficient of xenon?

A

0.14

36
Q

What is the oil:blood partition coefficient of halothane?

A

224

37
Q

What is the oil:blood partition coefficient of isoflurane?

A

98

38
Q

What is the oil:blood partition coefficient of enflurane?

A

98

39
Q

What is the oil: blood partition coefficient of desflurane?

A

29

40
Q

What is the oil:blood partition coefficient of sevoflurane?

A

80

41
Q

What is the oil:blood partition coefficient of nitrous oxide?

A

1.4

42
Q

What is the oil:blood partition coefficient of xenon?

A

1.9

43
Q

What is the odour of halothane?

A

Sweet

44
Q

What is the odour of isoflurane?

A

Irritant

45
Q

What is the odour of enflurane?

A

Non-irritant

46
Q

What is the odour of desflurane?

A

Pungent

47
Q

What is the odour of sevoflurane?

A

Non-irritant

48
Q

What is the odour of nitrous oxide?

A

Odourless

49
Q

What is the odour of xenon?

A

Odourless

50
Q

Which factors increase MAC?

A

Infancy
Hyperthermia
Hyperthyroidism
Hypernatraemia
Catecholamines
Sympathomimetics
Chronic EtOH
Chronic opiate use
Acute amphetamine use

51
Q

Which factors decrease MAC?

A

Neonatal period
Advanced age
Pregnancy
Hypotension
Hypothermia
Hypothyroidism
Alpha-2 agonists
Sedatives
Acute EtOH
Acute opiate use
Chronic amphetamine use
Lithium

52
Q

Which factors decrease the time taken to reach equilibrium of anaesthetic agent?

A

Increased alveolar ventilation
Decreased FRC
Increased FiAA
Reduced cardiac output
Reduced blood:gas partition coefficient
Second gas effect

53
Q

Which metabolic system is responsible for metabolising the C-(halogen) bond?

A

CYP450 (CYP2E1)

54
Q

In which order do volatile agents affect cardiac contractility (most -> least)

A

Halothane > Enflurane > Isoflurane > Sevoflurane > Desflurane

55
Q

What is xenon?

A

An inert, odourless, noble gas that makes up about 8.7 x10^-6 % of the atmosphere.

56
Q

How is xenon produced?

A

By fractional distillation of air

57
Q

How expensive is xenon?

A

Very.
Over 2000x the cost of an equivalent amount of N₂O

58
Q

What is the atomic number of xenon?

A

54

59
Q

What is the critical temperature of xenon?

A

16.6

60
Q

What is the mechanism of action of xenon?

A

Inhibition of glutamate at the NMDA receptor producing anaesthesia and analgesia.
Also blocks 5HT3 receptors, although is hasn’t been shown to have an effect on PONV.

61
Q

What are the effects of xenon on the cardiovascular system?

A

Minimal effects on CO, although mildly vagolytic producing a small decrease in HR.
Has some ischaemic preconditioning properties

62
Q

What are the effects of xenon on the respiratory system?

A

Reduction in RR
Increase in VT
Overall unchanged MV
Will produce apnoea in high enough concentration

63
Q

What are the effects of xenon on the CNS?

A

Likely neuroprotective
Small variable increases in CBR, so not recommended for neurosurgery

64
Q

What is the critical pressure of N₂O?

A

72 bar

65
Q

Is N₂O a vapour or a gas?

A

Both, it is inhaled as a vapour, and exhaled as a gas.

66
Q

How is N₂O produced?

A

Thermal decomposition of ammonium nitrate (NH4NO3) at 250°C

67
Q

What other compounds are produced alongside N₂O?

A

Nitric oxide (NO
Nitrogen dioxide (NO₂)
Nitric acid (HNO₃)
Ammonia (NH₃)
Nitrogen (N)
Water (H₂O)

68
Q

How are the unwanted side products removed during N₂O production?

A

Acid/Alkali wash

69
Q

How is N₂O stored?

A

As a liquid with a pressure of 52 bar (the SVP of the vapour above the liquid)

70
Q

What colour cylinders are used to store N₂O?

A

French blue

71
Q

Define filling ratio?

A

The ratio of the mass of liquid N₂O compared to if filled with water

72
Q

What is the filling ratio of N₂O?

A

0.75 in UK
0.67 in tropics

73
Q
A
74
Q

What is the mechanism of action of N₂O?

A

Inhibition of NMDA receptor resulting in analgesia and sedation.

75
Q

What are the effects of N₂O on the cardiovascular system?

A

Decreased myocardial contractility offset by increase in central sympathetic outflow.
In heart failure this can cause decompensation.
No sensitisation to catecholamines.

76
Q

What are the effects of N₂O on the respiratory system?

A

Small reduction in VT
Small increase in RR
No net change in MV

77
Q

What are the effects of N₂O on the CNS?

A

Increase in CBF and CMRO₂ - avoid in neurosurgery and head injury

78
Q

Give some undesirable side effects of N2O.

A

Inhibition of B12 → cobalt ion at the centre of B12 is oxidised making it unsuitable to act as a cofactor in methionine synthesise → can lead to reduced DNA synthesis + megaloblastic anaemia
Subacute combined degeneration of the cord occurs by a similar mechanism
Expands gas-filled spaces

79
Q

What is entonox?

A

A 50:50 mix of N₂O and O₂

80
Q

How is entonox stored?

A

French blue cylinders with a white and blue checkered shoulder at 137 bar

81
Q

What is the metabolism of isoflurane?

A

The liver metabolises isoflurane to trifluoroacetic acid (TFA) and inorganic fluoride ions
Only about 0.2% of isoflurane is metabolised, with the rest being exhaled unchanged

82
Q

What is the metabolism of isoflurane?

A

The liver metabolises enflurane to trifluoroacetic acid (TFA) and inorganic fluoride ions
Only about 2% of enflurane is metabolised, with the rest being exhaled unchanged

83
Q

What is the metabolism of sevoflurane?

A

The liver metabolises sevoflurane to trifluoroacetic acid (TFA) and inorganic fluoride ions
Only about 3% of sevoflurane is metabolised, with the rest being exhaled unchanged

84
Q

What is the metabolism of halothane?

A

20% metabolised

Oxidative metabolism:
The primary pathway for metabolising halothane, catalysed by CYP2E1 → chloride + bromide + trifluoroacetic acid → acute hepatitis

Reductive metabolism:
A minor pathway for metabolising halothane, catalysed by CYP2A6 and CYP3A4 → fluoride + bromide ions