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24 Anesthesia Pharm > Inhaled Anesthetics Part 1 (Exam III) > Flashcards

Inhaled Anesthetics Part 1 (Exam III) Flashcards

1
Q

What is Boyle’s Law?
What application of this was mentioned in class?

A
  • Pressure and Volume of gas are inversely proportional
  • Bellows contract thus increasing circuit pressure → gasses flow from high pressure circuit to low pressure lungs.
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2
Q

What is Fick’s Diffusion Law (as is pertinent to inhaled anesthetics)?

A

Once air molecules enter alveoli, they move around randomly and begin to diffuse into the pulmonary capillaries.

“the rate of diffusion of a substance across unit area (such as a surface or membrane) is proportional to the concentration gradient”

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3
Q

What factors is diffusion dependent on?

A
  • Partial pressure gradient of the gas
  • Solubility of the gas
  • Thickness of the membrane
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4
Q

What is Graham’s Law of Effusion?

A

Process by which molecules diffuse through pores and channels without colliding.
- smaller molecules effuse faster dependent on solubility (diffusion)

Ex. CO2 a wt 44g is 20x more diffusible compared to O2 wt 32.

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5
Q

Smaller molecules effuse faster dependent on ________.

A

solubility

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6
Q

Which diffuses faster CO₂ or O₂ ? Why?
Which would you expect to diffuse faster?

A

CO₂ is 20x more diffusible due to solubility despite O₂ weighing less.

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7
Q

When PA equals ________, then the inhaled gas concentration equals the exhaled gas concentration and the patient is unconscious.

A

PBrain

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8
Q

If PBrain is greater than PA then what we expect to be occurring? Why?

A

The patient should be waking up. This means the exhaled gas is greater than the inhaled gas and the concentration gradient is moving towards the alveoli away from the brain.

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9
Q

What does the following equation mean?

PA ⇌ Pa ⇌ PBrain

A

This is comparing the partial pressure of volatile gas in the alveoli to the arterial blood to the brain.

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10
Q

What input factors affect the diffusion of volatile gas from the anesthetic machine to the alveoli?

A
  • Inspired partial pressure
  • Alveolar ventilation
  • Anesthetic system re-breathing
  • FRC
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11
Q

Which factors affect the uptake of anesthetic gas from the alveoli to the blood?

A
  • Blood:gas partition coefficient
  • Cardiac output
  • A-V partial pressure difference
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12
Q

How would a low cardiac output affect the diffusion of anesthetic gas from the alveoli to the pulmonary capillary blood?

A

↓CO = more time to diffuse across the alveolus

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13
Q

What factors affect the uptake of anesthetic gas from the arterial blood to the brain?

A
  • Brain:Blood partition coefficient
  • Cerebral blood flow
  • a-v partial pressure difference.
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14
Q

Gas goes from a ____ gradient to a ____ gradient in order to reach a steady state.

A

high; low

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15
Q

What does PI mean?

A

Partial pressure of inspired volatile gas.

Needs verification.

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16
Q

How can gas be “forced” to the brain quicker?

A

“Over pressurization”
By increasing PI. This creates a higher gradient for the gas to flow from PA → Pa → PBrain

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17
Q

What does FE/FI mean?

A

FE/FI is the ratio of expired gas to inspired gas.

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18
Q

What concept is this chart conveying?

A

Concentration Effect: essentially, ↑concentration inspired gas = ↑PA = increased rate of diffusion

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19
Q

What is over-pressurization?

A
  • A large increase in PI so as to force gas from PA → Pa → PBrain much faster.
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20
Q

What would sustained delivery of over-pressurization result in?

A

Overdose

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21
Q

What gas does the second gas effect always apply to?

A

N₂O (nitrous oxide)

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22
Q

What is the second gas effect as it relates to anesthesia?

A
  • Uptake of a high-volume gas (N₂O) accelerates a concurrently administered volatile gas.
  1. High volume of N2O uptake into pulmonary cap
  2. Increases concentration of 2nd gas
  3. Increase uptake of 2nd gas due to gradient created by N2O
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23
Q

How does N₂O create the second gas effect?

A

N₂O hyper-concentrates volatiles to create a high concentration gradient by being super-diffusible (due to large partial pressure not solubility).

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24
Q

Describe what is being depicted on the graph below.

A
  • This is the concentrating effect of N₂O on halothane.
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25
Q

What cases would nitrous oxide not be utilized in?
Why?

A
  • Cases with an air-filled cavity
  • N₂O will diffuse into the cavity and fill it. (extent of damage dependent on the compliance of the cavity).
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26
Q

What specific cases are bad for the usage of N₂O?

A
  • Ear & eye
  • Open belly
  • Lung
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27
Q

What factors affect the degree of pressure N₂O would exert on a cavity that it filled?

A
  • Partial pressure of N₂O
  • Blood flow to the cavity
  • Duration of N₂O administration
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28
Q

What would nitrous inhalation in a patient with pneumothorax do?

A

Expand the pneumothorax

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29
Q

What could N₂O on an intraocular case do?

A
  • Massively increase retinal artery pressure and cause permanent vision loss.
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30
Q

Decreased ______ from hyperventilation will decrease cerebral blood flow and limit induction speed.

A

PaCO₂

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31
Q

What is the definition of solubility for anesthetic gasses?

A

Ratio of how inhaled gas distributes between two compartments at equilibrium (when partial pressures are equal).

the relative capacity of each compartment to hold the volatile

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32
Q

If the temperature of blood increases then solubility ______.

A

decreases

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33
Q

What does a low blood solubility mean for induction?

A

Less gas has to be dissolved = PA → Pa is rapid = rapid induction & recovery.

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34
Q

What does a high blood solubility mean for induction?

A

More gas has to be dissolved = PA → Pa is slow = slow induction & recovery.

35
Q

What is being described in the graph below?

A

Fa/Fi and solubility
How quickly the inspired concentration of a gas equals the alveolar concentration of the gas.

36
Q

What volatile gasses are intermediately soluble?

A
  • Halothane
  • Enflurane
  • Isoflurane
37
Q

What is the blood:gas partition coefficient of halothane?

A

Halothane = 2.54

38
Q

What is the blood:gas partition coefficient of enflurane?

A

Enflurane = 1.90

39
Q

What is the blood:gas partition coefficient of Isoflurane?

A

Isoflurane = 1.46

40
Q

What volatile gasses are poorly soluble?

A
  • N₂O
  • Desflurane
  • Sevoflurane
41
Q

What is the blood:gas partition coefficient of N₂O?

A

Nitrous = 0.46

42
Q

What is the blood:gas partition coefficient of Desflurane?

A

Desflurane = 0.42

43
Q

What is the blood:gas partition coefficient of Sevoflurane?

A

Sevoflurane = 0.69

44
Q

What are the blood:gas solubilities of all the gasses we have to know for anesthesia pharm?

A
45
Q

What occurs (in regards to our partial pressure gradients) during emergence from anesthesia?

A

Concentration gradient reverses.

PA ← Pa ← PBrain

46
Q

What helps decrease concentration of volatile anesthetic in PA and PBrain on emergence?

A

Continued uptake by Muscle/Fat if not already at equilibrium.

47
Q

What color coding does isoflurane have?

A

Purple

48
Q

What color coding does sevoflurane have?

A

Yellow

49
Q

What color coding does desflurane have?

A

Blue

50
Q

Which anesthetic would you anticipate as having the quickest recovery?
Slowest?

A

Fastest recovery = desflurane
Slowest recovery = halothane

51
Q

What is 1 MAC?

A

Concentration at 1atm that prevents skeletal muscle movement in response to supramaximal painful stimulation in 50% of patients.

52
Q

What is 1.3 MAC?

A

Concentration at 1atm that prevents skeletal muscle movement in response to surgical stimulation in 99% of patients.

53
Q

What would ED99 be equivalent to in regards to MAC?

A

ED99 ≈ 1.3 MAC

54
Q

What is MACawake?

A

0.3 - 0.5 MAC: partial awakeness and responsiveness.

“the concentration required to block voluntary reflexes and control perceptive awareness”

55
Q

What is MACBAR?

A

1.7 - 2.0 MAC: Blunts autonomic responses. No SNS response at all, essentially an overdose.

56
Q

What patient are standardized MAC values based on?

A

30 - 55 y/o at 37°C (98.6 F) at 1atm

57
Q

What is the MAC of N₂O?
What does this mean?

A

N₂O MAC = 104%. Can’t be used as sole anesthetic agent. (104% MAC can not be reached at 1 ATM!)

58
Q

What is the MAC of Halothane?

A

0.75%

59
Q

What is the MAC of Enflurane?

A

1.63%

60
Q

What is the MAC of Isoflurane?

A

1.17%

61
Q

What is the MAC of Desflurane?

A

6.6

62
Q

What is the MAC of Sevoflurane?

A

1.8%

63
Q

What are the two biggest factors that affect MAC?

A
  • Body temperature
  • Age
64
Q

At what age does MAC need peak?

A

1 y/o

65
Q

How much does MAC need decrease as one gets older?

A

6% per decade.

66
Q

What factors will increase MAC?

A
  • Hyperthermia
  • Excess Pheomelanin (redheads)
  • Drug-induced ↑ catecholamines
  • Hypernatremia
67
Q

What factors will decrease MAC?

Extensive list

A

Essentially anything that slows metabolism

  • Hypothermia
  • Pre-op meds
  • Intra-op opioids
  • α-2 agonists (Dex, clonidine)
  • Acute EtOH
  • Pregnancy
  • Early post-partum
  • Lidocaine
  • PaO₂ < 38 mmHg
  • Mean BP < 40mmHg
  • Cardiac Bypass
  • Hyponatremia
68
Q

How does loss of consciousness occur with the use of volatile anesthetics?

A
  • Potentiation of GABAA in the brain. (RAS - recticular activating system)
  • Potentiation of glycine in the brainstem.
69
Q

Which of these two liquids in enclosed containers has the higher vapor pressure?

A

Liquid B: more evaporative.

Vapor pressure is the pressure at which vapor and liquid are at equilibirum.

70
Q

What is Dalton’s law?

A
  • The sum of all partial pressures will equal the total pressure.
  • Ptotal = Pgas1 + Pgas2…
71
Q

What is Henry’s Law?

A

The amount of dissolved gas in a liquid is proportional to its partial pressure above the liquid.

72
Q

What does Henry’s law mean in practice?

A

Henry’s Law is pertinent to overpressurization.

If partial pressure of a volatile doubles, then double the molecules will interact with Pa from the alveoli.

73
Q

Heat will _____ vapor pressure.

A

increase

74
Q

Cold temperatures will _____ vapor pressure.

A

decrease.

75
Q

A lower vapor pressure gas is inherently more volatile. T/F ?

A

False. ↑vapor pressure = ↑volatility

76
Q

What is the vapor pressure of halothane?

A

243

77
Q

What is the vapor pressure of Enflurane?

A

175

78
Q

What is the vapor pressure of Isoflurane?

A

238 torr (mmHg)

79
Q

What is the vapor pressure of Desflurane?

A

669 torr

80
Q

What is the vapor pressure of Sevoflurane?

A

157 torr (or mmHg)

81
Q

What is the variable bypass on the anesthetic machine?

A

A way to dilute/concentrate the amount of anesthetic gas reaching the patient.

82
Q

What is the splitting ratio?

A

How much gas is being sent into the vaporizer

83
Q

What is the purpose of the wicks found in the vaporizing chamber below?

A

The wicks increase gas-liquid interface and improve vaporization.

24 Anesthesia Pharm (20 decks)

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