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My Primary Deck > Volatile Anaesthetics > Flashcards

Volatile Anaesthetics Flashcards

1
Q

Mean Alveolar Concentration

A

The alveolar concentration of a gaseous agent required to ensure that 50% of a test population at sea level does not respond to a standard surgical skin incision

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2
Q

Dose-response curve for volatile agents

A

20% below MAC - almost all patients move in response to surgical stimulus
20% above MAC - less than 5% of patients move

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3
Q

Blood:Gas Coefficient

A

If a substance has a high blood:gas coefficient, it easily dissolves into the blood resulting in a low partial pressure. This results in a slower onset and offset of anaesthesia (paradoxically)

A measure of how quickly Fa/Fi approaches 1 - no units!

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4
Q

Oil:Gas Coefficient

A

If the Oil:Gas coefficient is high, the substance is more lipid soluble and therefore tends to pass readily into lipid rich organs e.g. the brain. Potency is proportional to O:G (Meyer-Overton)

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5
Q

Factors Decreasing MAC

A 
Pregnancy, neonates, old age
Chronic amphetamine use
Acute alcohol intoxication
Acute opioid use
Lithium, benzodiazepines and lidocaine
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6
Q

Factors Increasing MAC

A 
Infancy
Acute amphetamine use
Hyperthermia, hyperthyroidsim, hypernatraemia
Chronic alcoholism
Chronic opioid use
Catecholamines and sympathomimetics
Stress response
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7
Q

Enflurane: MAC

A

MAC 1.7

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8
Q

Enflurane: Oil:Gas coefficient

A

O:G 98

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9
Q

Enflurane: Blood:Gas coefficient

A

B:G 1.9

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10
Q

Isoflurane: MAC

A

MAC 1.2

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11
Q

Isoflurane: Oil:Gas coefficient

A

O:G 98

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12
Q

Isoflurane: Blood:Gas coefficient

A

B:G 1.4

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13
Q

Sevoflurane: MAC

A

MAC 1.8

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14
Q

Sevoflurane: Oil:Gas coefficient

A

O:G 80

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15
Q

Sevoflurane: Blood:Gas coefficient

A

B:G 0.7

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16
Q

Desflurane: MAC

A

MAC 6.6

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17
Q

Desflurane: Oil:Gas coefficient

A

O:G 29

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18
Q

Desflurane: Blood:Gas coefficient

A

B:G 0.4

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19
Q

Halothane: MAC

A

MAC 0.8

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20
Q

Halothane: Oil:Gas coefficient

A

O:G 224

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21
Q

Halothane; Blood Gas coefficient

A

B:G 2.2

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22
Q

Carbon dioxide absorbants

A 
UK: sodium hydroxide
USA: potassium hydroxide (baralyme)
Requires water
H20 + CO2 -> H2CO3 (carbonic acid)
H2CO3 + 2NaOH -> Na2CO3 +2H2O
Na2CO3 + Ca(OH)2 -> CaCO3 + 2NaOH
Sodium carbonate + calcium hydroxide -> Calcium carbonate + sodium hydroxide
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23
Q

Enflurane: structure

A

Molecular weight: 184

Structural isomer of isoflurane

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24
Q

Isoflurane: structure

A

Molecular weight: 184

Structural isomer of enflurane

25
Q

Sevoflurane: structure

A

Molecular weight: 200

Sevoflurane is achiral

26
Q

Halothane: structure

A

Molecular weight: 197

27
Q

Desflurane: structure

A

Molecular weight: 168

28
Q

Desflurane: boiling point

A

23.5°C (requires specialized Tec 6 vaporizer)

29
Q

Desflurane: SVP at 20°C

A

89.2 kPa

30
Q

Enflurane: boiling point

A

56.5°C

31
Q

Enflurane: SVP at 20°C

A

23.3 kPa

32
Q

Halothane: boiling point

A

50.2°C

33
Q

Halothane: SVP at 20°C

A

32.3 kPa

34
Q

Isoflurane: boiling point

A

48.5°C

35
Q

Isoflurane: SVP at 20°C

A

33.2 kPa

36
Q

Sevoflurane: boiling point

A

58.5°C

37
Q

Sevoflurane: SVP at 20°C

A

22.7 kPa

38
Q

Desflurane: cardiovascular effects (contractility, heart rate, systemic vascular resistance, blood pressure, coronary steal, splanchic blood flow, catecholemine sensitization)

A 
Contractility: minimal
Heart rate: increased (increased ++ at MAC > 1.5).  Can induce tachycardia and hypertension at MAC > 1 (classic MCQ question)
Systemic vascular resistance: --
Blood pressure: --
Coronary steal: no
Splanchic blood flow: unchanged
Catecholemine sensitization: nil
39
Q

Enflurane: cardiovascular effects (contractility, heart rate, systemic vascular resistance, blood pressure, coronary steal, splanchic blood flow, catecholemine sensitization)

A 
Contractility: --
Heart rate: +
Systemic vascular resistance: -
Blood pressure: --
Coronary steal: No
Splanchic blood flow: -
Catecholamine sensitization: +
40
Q

Halothane: cardiovascular effects (contractility, heart rate, systemic vascular resistance, blood pressure, coronary steal, splanchic blood flow, catecholemine sensitization)

A 
Contractility: ---
Heart rate: --
Systemic vascular resistance: -
Blood pressure: ---
Coronary steal: No
Splanchic blood flow: -
Catecholamine sensitization: +++ (causes arrhythmias)
41
Q

Isoflurane: cardiovascular effects (contractility, heart rate, systemic vascular resistance, blood pressure, coronary steal, splanchic blood flow, catecholemine sensitization)

A 
Contractility: -
Heart rate: ++ (this reflex tachycardia suggests that the carotid sinus reflex is preserved)
Systemic vascular resistance: --
Blood pressure: --
Coronary steal: Possibly
Splanchic blood flow: Unchanged
Catecholamine sensitization: Nil
42
Q

Sevoflurane: cardiovascular effects (contractility, heart rate, systemic vascular resistance, blood pressure, coronary steal, splanchic blood flow, catecholemine sensitization)

A 
Contractility: -
Heart rate: nil effect
Systemic vascular resistance: -
Blood pressure: -
Coronary steal: No
Splanchic blood flow: Unchanged
Catecholamine sensitization: Nil
43
Q

The volatile most likely to cause arrhythmia secondary to catecholamine sensitization

A

Halothane

44
Q

The volatile most likely to cause coronary steal syndrome

A

Isoflurane

45
Q

Desflurane: CNS effects (cerebral blood flow, cerebral O2 requirements, EEG, potentiation of muscle relaxants, analgesia)

A 
Cerebral blood flow: +
Cerebral O2 requirements: -
EEG: burst supression
Potentiation of muscle relaxants: significant
Analgesia: some
46
Q

Isoflurane: CNS effects (cerebral blood flow, cerebral O2 requirements, EEG, potentiation of muscle relaxants, analgesia)

A

Cerebral blood flow: + (nil if MAC<1)
Cerebral O2 requirements: autoregulation preserved
EEG: burst supression
Potentiation of muscle relaxants: some relaxation
Analgesia: some

47
Q

Sevoflurane: CNS effects (cerebral blood flow, cerebral O2 requirements, EEG, potentiation of muscle relaxants, analgesia)

A 
Cerebral blood flow: +
Cerebral O2 requirements: -
EEG: burst supression
Potentiation of muscle relaxants: some relaxation
Analgesia: some
48
Q

Enflurane: CNS effects (cerebral blood flow, cerebral O2 requirements, EEG, potentiation of muscle relaxants, analgesia)

A

Cerebral blood flow: +
Cerebral O2 requirements: -
EEG: Epileptiform activity (3Hz spike and wave)
Potentiation of muscle relaxants: significant
Analgesia: some

49
Q

Halothane: CNS effects (cerebral blood flow, cerebral O2 requirements, EEG, potentiation of muscle relaxants, analgesia)

A 
Cerebral blood flow: +++
Cerebral O2 requirements: -
EEG: burst supression
Potentiation of muscle relaxants: some relaxation
Analgesia: none
50
Q

Desflurane: metabolism

A

0.02%

51
Q

Enflurane: metabolism

A

2%

52
Q

Halothane: metabolism

A

20%
Can cause Type I (benign, self limiting) or Type II (severe) hepatotoxicity via T-cell mediated inflammation
Metabolism to trifluoroacetic acid under oxidative conditions - implicated in Type II hepatotoxicity
Reductive metabolism to F-C-Br bonds are more easily metabolised than C-F bonds

53
Q

Isoflurane: metabolism

A

0.2% - non toxic

NB due to the -CHF2 group, it may react with dry soda lime producing carbon monoxide e.g. in circle system that has been left with dry gas circulating over the weekend

54
Q

Sevoflurane: metabolism

A

3.5%
Undergoes hepatic metabolism by cytochrome P450 (isoform 2E1) to produce hexafluoroisopropanol and inorganic fluoride ions (known to cause renal toxicity)

55
Q

Compound A

A

Created when sevoflurane is used in the rpesence of carbon dioxide absorbents
More readily produced with (dry) potassium hydroxide
Human nephrotoxic threshold of 150-200 ppm.
At flow rates of 0.25l/min for 5 hours, compound A level < 20ppm (therefore unlikely to cause harm in anaesthesia)

56
Q

Sevoflurane: manufacture

A

One pot method - all the ingredients are added together to produce sevoflurane and then water is added to 300ppm
Chloro-fluoro method - basic molecular architecture is manufactured but with chlorine attached. This is then substituted with fluorine

57
Q

Sevoflurane: respiratory effects

A

Pleasant odor
Depresses ventilation with reduction in minute volume
Inhibits pulmonary vasoconstriction

58
Q

Sevoflurane: storage

A

Can produce hydrofluoric acid if stored in glass or with concentration of added water <100ppm (attack by Lewis acids) - hydorfluoric acid corrodes glass
Therefore formulated with 300ppm water and stored in polyethylene napthalate bottles (alternatively in aluminium bottle with resin laqcuer - can be formulated with <130ppm water)

59
Q

Halothane: respiratory effects

A

Sweet, non-irritant odour
Bronchodilatory
High concentrations significantly reduce ventilation

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