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Pharmacology Basics > VOLATILE AGENTS > Flashcards

VOLATILE AGENTS Flashcards

1
Q

How is N2O stored:

  • What state & cylinder?
  • What gauge pressure?
  • Critical temperature?
  • Critical pressure?
A

Stored as a liquid
French blue cylinder
Gauge pressure: 51 bar at 20 degrees C

Critical temp: 36.5 degrees C
Critical Pressure: 72 bar

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2
Q

N2O:

  • MAC?
  • Systemic effects
A

MAC - 105% (highest mac)

Increases CBF, minimal respiratory changes, CVS increases sympathetic stimulation but also myocardial depression.

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3
Q

N2O –>
Blood: gas Coefficient?
Oil: gas coefficient?

A

blood: gas - > 0.47 (des, n2o, sevo)
oil: gas - > 1.4 (lowest value)

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4
Q

N2O:
Boiling point?
Percentage metabolised?

A

Boiling point:
- 89 degrees C (at 1 atmosphere)

Zero metabolised

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5
Q

ENTONOX:
?mixture
?how is it stored
?pseudocritical temperature

A

Stored as 50:50 mixture of O2 and N2O, dissolved into each other.
Stored in checked french blue cylinders at 137 bar (G, J)

Pseudocritical temp: - 5.5 at 117 bar (separate into constinuent parts)

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6
Q

Describe ISOFLURANE:

  • molecular form
  • Resp effect
  • CVS effect
  • CNS effect
A
  • halogenated methyl ether, structural isomer of enflurane

Resp: depresses ventilation more than Halothane, less than enflurane. MV decreased, PaCo2 increased, RR +.
Bronchodilation, but pungent smell causes upper airway irritability.

CVS: reduce SVR, reflex tachycardia

CNS: best balance of cerebral O2 requirement and minimal increase in CBF

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7
Q

ISOFLURANE:

MAC, BG, OG, Boiling point

A

MAC = 1.17

Blood: gas = 1.4

Oil: gas = 98

Boiling point - 48.5

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8
Q

ISOFLURANE:
? percentage metabolised
? toxicity

A

0.2% metabolised

Toxicity: may react with dry soda lime/ baralyme to produce carbon monoxide due to -CHF2 group

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9
Q

SEVOFLURANE:
? molecular form
? chiral
?systemic effects

A
  • polyflourinated isopropyl methy ether
  • achiral

RESP: pleasant odour, good for induction. Depresses ventilation.

CVS: reduced SVR, no change in HR, therefore low BP.

CNS: compared to halothane higher incidence of post op agitation and delirium in children.

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10
Q

SEVOFLURANE:

MAC, BG, OG, Boiling point

A

MAC - 2

B:G - 0.68

Oil: gas - 80

Boiling point - 58.5 degrees

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11
Q

SEVOFLURANE:
? boiling point
? percentage metabolised
? what enzyme metabolises

A

boiling point - 58 degrees C

5% metabolised by CYP450 - 2E1 isoform. Produces hexaflouroisopropanol and inorganic F (renal toxicity)

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12
Q

SEVOFLURANE:

? toxicity

A

When used in the presence of carbon dioxide adsorbers, compounds A, B, C, D, E are identified.

Compound A and B are present to detectable levels, and are favoured by potassium hydroxide rather than sodium hydroxide based adsorbents.

The reaction releases heat and uses up Sevo.

Not shown to produce lethal amounts even with low flows and prolonged surgery, no renal impairment found.

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13
Q

SEVOFLURANE:

Problems with storage?

A

During storage if the water added is below 100ppm it is susceptible to attack by Lewis acids at ether and hydrogen bonds, releasing toxic hydroflouric acid (this corrodes glass).

Therefore it is mixed with 300ppm water and stored in polyethelene naphthalate bottles.

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14
Q

ENFLURANE:

  • structural form
  • interference with EEG?
  • advise in renal impairment?
A
  • halogenated methyl ether, structural isomer of isoflurane
  • at high concentrations, produces 3 Hz spike and pattern on EEG, consistent with grand mal activity
  • avoid in renal impairment due to metabolised product of flouride ions (known to produce reversible nephropathy)
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15
Q

ENFLURANE:

MAC, BG, OG, Boiling point

A

MAC - 1.68

B:G - 1.8

Oil: gas - 98

Boiling point - 56.5 degrees

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16
Q

ENFLURANE:
? boiling point
? % metabolised

A

boiling point - 56.5 degrees C

2% metabolised - fluoride ions that can cause reversible nephropathy.

17
Q

Molecular weight of volatile agents, heaviest to lightest

A 
Sevoflurane   (200.1) 
Halothane   (197)
Isoflurane / Enflurane   (184.5)
Desflurane   (168) 
Xenon   (131) 
N2O   (44) - same as CO2
18
Q

Halothane:

MAC, BG, OG, boiling point

A

MAC - 0.75

BG - 2.4

OG - 224

Boiling point - 50 C

19
Q

Desflurane:

MAC, BG, OG, Boiling point

A

MAC - 6.6

BG - 0.42

OG - 29

Boiling point - 23.5

20
Q

Which agents most significantly increase CBF?

Which does not below a MAC of 1?

A

Halothane increases it the most.

Isoflurane does not under MAC < 1

21
Q

Which agent can cause an epileptiform EEG?

A

Enflurane - epileptiform 3Hz wave spikes.

22
Q

Which agent has no effect on analgesia?

A

Halothane

23
Q

Which agents have the lowest BG?

Lowest to highest

A

Xenon - 0.14
Desflurane - 0.42
N20 - 0.47
Sevo - 0.7

Iso - 1.4
Enflo - 1.8
Halothane - 2.40

X-DNS IEH

24
Q

Which agents have the highest OG?

Highest to lowest

A

Halothane - 224
Iso/En - 98
Sevo - 80

Des - 29
Xenon - 1.9
N20 - 1.4

HIS DXN

25
Q

Which volatile can cause coronary steal syndrome?

A

Isoflurane

26
Q

Which volatile can inhibit pulmonary vasoconstriction?

A

Sevoflurane

27
Q

Which volatiles have the highest and lowest molecular weight?

A

Sevoflurane 200

Halothane 197

Isoflurane / Enflurane 184.5

Desflurane 168

Xenon 131

N2O 44.

28
Q

Why is it unsafe to give halothane with infiltration of adrenaline doses > 100 mcg/min?

A

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

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

29
Q

Which volatile induces tachycardia and hypertension at MAC values > 1

A

Desflurane

30
Q

What pin index is nitrous oxide stored at?

A

The configuration for nitrous oxide is 3 and 5.

31
Q

What pin index is oxygen stored in?

A

The configuration for oxygen is 2 and 5.

32
Q

How is halothane prepared in solution?

A

It is prepared with 0.01% thymol to prevent decomposition by light.

33
Q

Why is halothane likely to cause brady/ vagal stimulation?

A

It may also cause bradycardia by inhibiting atrioventricular conduction / activity.

Pharmacology Basics (25 decks)

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