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Anesthesiology > 5: Inhalation Anesthetics 1 > Flashcards

5: Inhalation Anesthetics 1 Flashcards

1
Q

Most modern inhalational anesthetics are _____, not _____.

A

vapor, gas

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2
Q

When does gas exist in a gaseous form?

A

At room temp and at sea level

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3
Q

When does a vapor exist in a liquid form?

A

At room temp and at sea level

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4
Q

Most inhalants we use are _____.

A

vapors

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5
Q

What is the critical temperature?

A

Temp at and above which a vapor cannot be liquified, no matter how much pressure is applied

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6
Q

A vapor can be liquefied _____ the critical temp when enough _____ is applied.

A

below, pressure

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7
Q

What is the critical temp of isoflurane? Nitrous oxide?

A

Iso = ~200ºC

N2O = ~36.4ºC

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8
Q

What is the only gas that is routinely used?

A

Nitrous oxide

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9
Q

Maximal [] of a vapor is determined by saturated _____ _____.

A

vapor pressure

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10
Q

What is needed for delivery of a vapor?

A

vaporizer

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11
Q

What is saturated vapor pressure?

A

Max [] of molecules in the vapor phase that exists for a given liquid at a given temp; it is specific for each agent.

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12
Q

Saturated vapor pressure depends only on _____.

A

temperature

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13
Q

What is the saturated vapor pressure of sevoflurane?

What is its max [] at sea level?

A

SVP = 157 mmHg

Max [] = 21%

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14
Q

What is the saturated vapor pressure of halothane?

What is its max [] at sea level?

A

SVP = 243 mmHg

Max [] = 32%

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15
Q

What is the saturated vapor pressure of isoflurane?

What is its max [] at sea level?

A

SVP = 236 mmHg

Max [] = 31%

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16
Q

What is the saturated vapor pressure of desflurane?

What is its max [] at sea level?

A

SVP = 664 mmHg

Max [] = 87%

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17
Q

What is the saturated vapor pressure of nitrous oxide?

What is its max [] at sea level?

A

SVP = 38,000

Max [] = 100%

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18
Q

What is the formula for max [] at sea level?

A

Max [] = (SVP/barometric P) * 100%

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19
Q

How did the Morton Etherizer (1846) work?

A

Piece of gauze was soaked in liquid ether and placed in the chamber, liquid starts to turn to gas

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20
Q

What is the [] of iso in the vaporizing chamber of the vaporizer?

A

31%

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21
Q

What is the Minimum Alveolar Concentration (MAC)?

A

Alveolar [] at which 50% of animals do not move in response to a noxious stimulus (EX: clamping base of tail or on the toe).

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22
Q

T/F: A noxious stimulus for an animal when determining MAC can be making an incision.

A

False

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23
Q

How is MAC determined (6 steps)?

A
  1. An individual is anesthetized with the study drug
  2. The end tidal [] is measured and kept constant for at least 15 min
  3. A supramaximal noxious stimulus is applied
  4. If “no purposeful movement”, then the [] is decreased and kept constant for another 15 min
  5. Give the stimulus again, and if movement is seen, then the [] is increased
  6. [] value between response and no response = MAC
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24
Q

T/F: MAC does not vary much between spp

A

True

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25
Q

At steady state, P_____ inhalant = P_____ inhalant

A

Palveolar, Pbrain

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26
Q

What are advantages of MAC?

A
  1. Does not vary much between spp
  2. At steady state, Palveolar inhalant = Pbrain inhalant
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27
Q

What are 3 disadvantages of MAC?

A
  1. MAC determination is quantal - animal is either anesthetized or not
  2. MAC is determined on a population level only
  3. MAC definition depends on the end-point measurement (purposeful movement)
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28
Q

What is MAC for iso? What is the oil:gas PC?

A

MAC = 1.3%

Oil:gas PC = 98

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29
Q

What is the MAC for sevo? Oil:gas PC?

A

MAC = 2.4%

Oil:gas PC = 55

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30
Q

What is the MAC for desflurane? Oil:gas PC?

A

MAC = 7.2%

Oil:gas PC = 18.7

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31
Q

What is the MAC for nitrous oxide? Oil:gas PC?

A

MAC = 188%

Oil:gas PC = 1.4

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32
Q

What does a high oil:gas PC mean?

A

Drug is more fat-soluble, and therefore more potent

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33
Q

What gas is the most potent and why?

A

Isoflurane; has the highest oil:gas PC and the lowest MAC

34
Q

What is surgical MAC?

A

[] needed for 95% of patients not to move = 1.3-1.5x MAC

35
Q

What is surgical MAC of iso?

A

1.95%

36
Q

What is surgical MAC of sevo?

A

3.6%

37
Q

What is surgical MAC of desflurane?

A

10.8%

38
Q

Why is there no surgical MAC for nitrous oxide?

A

It is not possible to give normal MAC (188%), so not possible to give 1.5x MAC because you can only give 100% of a gas;

If you have 188% N2O you would kill your patient every time.

39
Q

What is the effect of other concurrent drugs on MAC? Give some examples.

A

They can decrease it;

Ace = decreases by up to 40%

Dexmedetomidine/opioids = decreases by 30-50%

N2O = decreases by 25-30%

40
Q

What are the effects of temperature on MAC?

A

Hyperthermia increases it to a point;

Hypothermia decreases it

41
Q

What is the effect of pregnancy on MAC?

A

It decreases it

42
Q

What is the effect of age on MAC?

A

It decreases it as age increases

43
Q

What is the effect of thyroid function on MAC?

A

Hyperthyroidism increases MAC

44
Q

Partial pressure of a drug in the _____ determines the partial pressure of the drug in the _____ and _____.

A

alveoli, blood, brain

45
Q

What are the steps of uptake and distribution of a drug/inhalant?

A
  1. Patient awake, vaporizer turned on
  2. Anesthetic delivered into trachea and lungs
  3. High [] of agent enters alveoli
  4. Agent diffuses across alveolar cell membrane –> blood
  5. [] of agent in blood increases
  6. Agent enters brain due to high lipid solubility and high blood flow to the brain
  7. Patient anesthetized
46
Q

When does anesthetic pressure in the alveoli first increase?

A

When the vaporizer is turned on

47
Q

The higher the _____ of anesthetic, the _____ the induction.

A

uptake, induction

48
Q

Inhalant uptake is affected by the agent _____.

A

solubility

49
Q

What does a blood:gas ratio of 0.5 mean?

A

Anesthetic is half as soluble in blood as in gas

50
Q

What does a blood:gas of 2.0 mean?

A

Anesthetic is twice as soluble in blood as in gas

51
Q

The _____ the solubility in blood, the _____ the agent is taken up by pumonary circulation, the _____ the induction.

A

higher, more, slower

52
Q

What is the B:G of halothane?

A

2.4

53
Q

What is the B:G of iso?

A

1.4

54
Q

What is the B:G of sevo?

A

0.65

55
Q

What is the B:G of nitrous oxide?

A

0.47

56
Q

What is the B:G of desflurane?

A

0.42

57
Q

What is the speed of induction and recovery of common inhalants, from slowest to fastest?

A

Halothane < Iso < Sevo < Nitrous oxide < Desflurane

58
Q

Rate of change at any time is proportional to the _____.

A

quantity at that time

59
Q

When does equilibrium occur?

A

When input = output

60
Q

How is time constant calculated and what does it mean?

A

= volume / flow

Describes speed at which a system can respond to change

61
Q

What is this?

A

Wash-in curve

62
Q

What is this?

A

Wash-out curve

63
Q

Your anesthesia machine has a rebreathing circuit with a 5 L volume. If your oxygen flow rate is set to 1 L/min and iso is set at 2%, how long will it take to accumulate 2% iso in the breathing circuit?

A

TC = volume/flow

TC = 5 L / 1 L/min = 5 min

Need 5 TC to reach new [] so 5 min x 5 = 25 min

64
Q

What is the Meyer-Overton rule?

A

Potency is related to oil solubility, so the lipid bilayer must be the site of action;

BUT not all lipid soluble drugs are general anesthetics

65
Q

What is the membrane protein theory?

A

Anesthetics bind proteins and modulate their functions;

Inhibitory vs. excitatory

66
Q

What receptor are anesthetics thought to bind to?

A

GABA - potentiates effect of GABA to increase flow of Cl

*This is a hypothesis, we are not 100% sure*

67
Q

Where are anesthetics thought to work to produce unconsiousness?

A

Cerebral cortex

68
Q

Where are anesthetics thought to work to produce analgesia?

A

Supra-spinal, dorsal horn

69
Q

Where are anesthetics thought to work to produce amnesia?

A

Hippocampus, amygdala

70
Q

Where are anesthetics thought to work to produce immobility?

A

Spinal cord

71
Q

What is the most important route of elimination?

A

via the lungs

72
Q

How is consciousness regained when an anesthetic is eliminated?

A

Regained as Pbrain anesthetic decreases

73
Q

Factors that speed _____ also speed elimination.

A

induction

74
Q

What type of inhalants will get eliminated faster?

A

Those with a low B:G coefficient (EX: Desflurane)

75
Q

What % of halothane is metabolized by the liver?

A

25%

76
Q

What % of iso is metabolized by the liver?

A

0.2%

77
Q

What % of sevo is metabolized by the liver?

A

2-5%

78
Q

What % of desflurane is metabolized by the liver?

A

0.02%

79
Q

What % of nitrous oxide is metabolized by the liver?

A

0.004%

80
Q

In order from best to worst, what are the anesthetics that can be used in patients with decreased liver function?

A

Nitrous oxide > Desflurane > Iso > Sevo > Halothane

Anesthesiology (12 decks)

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