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Exam Prep MCQs > Inhalational Agents > Flashcards

Inhalational Agents Flashcards

1
Q

What kind of isomer of enflurane is isoflurane?

A

A structural isomer

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2
Q

How does isoflurane affect the CVS?

A

Vasodilatation with reflex tachycardia, suggesting that baroreceptor function remains intact.

Hypotension with isoflurane is caused by reduced SVR. Myocardial function and cardiac output see only a small decrease.

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3
Q

What is the SVP of isoflurane?

A

32 kPa at 20C

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4
Q

What is the SVP of enflurane?

A

23.3 kPa at 20C

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5
Q

What % of isoflurane undergoes hepatic metabolism?

A

0.2%

Hepatic cytochrome P450 metabolizes the C - F bond.

Renal toxicity is rare due to low levels of fluoride ions produced.

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6
Q

What is the chloride group of isoflurane attached to?

A

The chiral centre

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7
Q

What effect do alpha 2 agonists have on MAC?

A

Decrease it

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8
Q

What does hypernatraemia do to MAC?

A

Increases MAC

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9
Q

What does chronic alcohol intake do to MAC?

A

Increases it

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10
Q

How does acute alcohol intake affect MAC?

A

Decreases MAC

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11
Q

Does the premature neonatal period affect MAC?

A

Mac is low in preterm neonates.

MAC value peaks at 1-6 months

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12
Q

Does sevoflurane have a chiral centre?

A

No

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13
Q

What happens to sevoflurane if its stored in glass?

A

This is highly toxic. Lewis acids degrade the ether and halogen bonds if sevoflurane is stored in water at concentrations less than 100ppm. The highly toxic hydrofluoric acid corrodes glass, driving Lewis acid production.

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14
Q

What is the blood:gas coeficient of isoflurane?

A

1.4

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15
Q

What is the blood: gas coefficient of sevoflurane?

A

0.7

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16
Q

Which gas causes coronary steal?

A

Isoflurane

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17
Q

Which cytochrome enzyme is responsible for sevoflurane/isoflurane/halothane metabolism?

A

CYP2E1

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18
Q

What does CYP3A4 metabolise?

A

Opiates and benzodiazepines

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19
Q

What is sevoflurane?

A

Polyfluorinated methyl isopropyl ether

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20
Q

What is the metabolism of sevoflurane?

A

3.5% undergoes hepatic metabolism to produce hexafluroisopropanol and fluoride ions

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21
Q

What gas undergoes renal metabolism to produce inorganic fluoride ions?

A

Methoxyflurane

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22
Q

When is Compound A production more likely?

A

In the presence of dry potassium hydroxide.

The suggested nephrotoxic threshold for compound A is 150-200 ppm. These levels that far exceed what is seen in clinical practise.

23
Q

What are the molecular weights of the gases?

A

N2O - 44

Xenon - 131

Desflurane - 168

Isoflurane/Enflurane - 184.5

Halothane - 197

Sevoflurane - 200.1

24
Q

What is the MAC of halothane?

A

0.75

25
Q

What are the MACs of enflurane and isoflurane?

A

Isoflurane 1.17

Enflurane 1.68

26
Q

What is the MAC for sevoflurane in 70% nitrous oxide?

A

May be as low as 0.7

27
Q

What is halothane?

A

A halogenated hydrocarbon.

There is no ether link so it’s not an ether.

28
Q

What is the SVP of halothane at 20C?

A

Halothane 32.3 kPa

Isoflurane 33.2 kPa

29
Q

Why can you not give 100mcg/min of adrenaline with halothane?

A

Halothane sensitises the heart to catecholamines, which may lead to arrhythmias - particularly ventricular tachycardias and bradyarrhythmias.

This dose of adrenaline should be administered over a 10 minute period.

30
Q

Which bonds of halothane are metabolised more easily?

A

Its C-Br bonds are metabolised with greater ease than its C-F bonds.

The C-F bonds are the most stable carbon-halogen bond.

31
Q

When does trifluoroacetyl chloride produced?

A

In halothane metabolism under oxidative conditions. This is implicated in halothane hepatitis.

32
Q

What is the boiling point of desflurane?

A

23.5 C

33
Q

What vaporiser is desflurane in?

A

Tec 6 - this heats it to 39C under a pressure of 2 atm

34
Q

What does desflurane cause with a MAC > 1?

A

Tachycardia and hypertension

35
Q

Which volatiles can produce carbon monoxide upon reaction with dry soda lime?

A

All the volatiles that contain -CHF2 molecule (isoflurane, enflurane, desflurane)

36
Q

Which has the higher blood:gas coefficient - desflurane or nitrous oxide?

A

Desflurane 0.42

Nitrous Oxide 0.47

37
Q

What is the critical pressure of nitrous oxide?

A

72 bar

38
Q

What is the critical temp of nitrous oxide?

A

36.5 C

39
Q

What is the pin index of O2?

A

2 and 5

40
Q

What is the pin index for nitrous oxide?

A

3 and 5

41
Q

Does nitrous oxide affect ICP or cerebral blood flow?

A

Yes, increases both

42
Q

What does nitrous oxide do to methionine synthetase?

A

It inhibits methionine synthetase by oxidising this cobalt ion on Vit B12.

It may also inhibit methionine synthetase directly. Nitrous oxide therefore inhibits methionine, thymidine, tetrahydrofolate and DNA synthesis.

43
Q

What will nitrous oxide reduce the MAC of isoflurane to when used at 70%?

A

0.5

44
Q

Which volatile gas increases cerebral blood flow the most?

A

Halothane (most)

Enflurane

Nitrous Oxide

Isoflurane (least)

45
Q

What is the smell of halothane?

A

Sweet odour

46
Q

What ions does halothane have?

A

1 bromide

1 chloride

3 fluoride ions

47
Q

Why is halothane prepared with 0.01% thymol?

A

To prevent decomposition by light

48
Q

Does halothane cause vagal stimulation?

A

Yes

It may also cause bradycardia by inhibiting atrioventricular conduction / activity

49
Q

How is Xenon metabolised?

A

All by the lung elimination

50
Q

Does isoflurane increase cerebral blood flow?

A

Not at concentrations below 1 MAC

51
Q

What is the critical pressure of O2?

A

50 bar

52
Q

What temperature does entonox separate into it’s constituent parts?

A

-7C (pseudocritical temp) at pressures of 117 bar

53
Q

What % of nitrous oxide is metabolised?

A

Less than 0.01%

54
Q
A

Exam Prep MCQs (19 decks)

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