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Pharmacology Exam 3 > Inhaled Anesthetics 1 (Exam 3) > Flashcards

Inhaled Anesthetics 1 (Exam 3) Flashcards

1
Q

Inhaled Anesthetics: Pharmacokinetics (ADME)

A
  • A: Uptake from alveoli into pulmonary capillary blood
  • D: determined by fat content and cardiac issues
  • M: not much metabolism; exhale drugs
  • E: Exhaled
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2
Q

Describe how age influences how we respond to Inhaled Anesthetics.

A
  • ↓ lean body mass
  • ↑ fat
  • ….↑ Vd for drugs (especially for more fat soluble)
  • ↓ clearance if pulmonary exchange is impaired
  • ↑ time constraints due to lower cardiac output
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3
Q

Describe Boyles law

A
  • Given a constant temperature –>
  • Pressure and volume of gas are inversely proportional
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4
Q

How do we apply Boyles Law to Inhaled anesthetics?

A
  1. As positive pressure ventilation begins, bellows contract
  2. Pressure increases within ventilator and circuit. (makes a pressure gradient)
  3. Anesthetic gases flow from high pressure to low pressure (lungs)
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5
Q

Fick’s diffusion depends on…..

A
  • partial pressure of the gas
  • Solubility of the gas (diffusion)
  • Thickness of the membrane
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6
Q

Describe Graham’s law of Effussion.

A
  • Process by which molecules diffuse through pores and channels without colliding
    * Smaller molecules effuse faster dependent on solubility (diffusion)
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7
Q

Name a gas that is an exception of Graham’s Law. Describe why.

A
  • Carbon dioxide. wt 44 g
  • Oxygen. wt 32 g
  • Carbon dioxide is more soluble
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8
Q

When we administer inhaled anesthetic, what is the end goal?

A

a. PA <–> Pα <–> PBr

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9
Q

Alveola Pressure is an indicator of:

A
  • depth of anesthesia
  • Recovery from anesthesia
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10
Q

Partial Pressure Gradients: Anesthetic Machine to Alveoli

A

INPUT
* Inspired partial pressure
* Alveolar ventilation
* Anesthetic breathing system (is there a lot of rebreathing)
* FRC

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11
Q

Partial Pressure Gradients: Alveoli to Blood

A

UPTAKE
* Blood gas partition coefficient
* Cardiac output
* A-v partial pressure difference

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12
Q

Partial Pressure Gradient: Arterial blood to brain

A

UPTAKE
* Brain:gas partition coefficient
* Cerebral blood flow
* a-v partial pressure difference

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13
Q

Describe the Concentration Effect

A

Impact of PI on the rate of rise of PA
* The higher the PI of a volatile, the more rapidly PA approaches PI
* Offsets uptake in Pa

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14
Q

Concentration Effect: Graph

A
  • 85%: fastest rate of rise and equal in 5-6
  • 50%- fast rate of rise: FI=FV
  • Higher the concentration, the faster they will go to sleep.
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15
Q

What are the effects of “Over Pressurization”

A
  • offsets slow induction from highly soluble volatiles
  • A large increase in PA
  • sustatained deliver at over pressurization can result in overdose
  • Ex: 1 vital capacity breath of high concentration SEVO = loss of eyelash reflex.
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16
Q

Describe Second gas effect

A
  • Uptake of a high-volume gas (N2O) accelerates concurrently administered companion gas– a volatile
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17
Q

How does Second Gas Effect work?

A
  • High volume of N2O uptake in pulmonary capillary
  • Increases concentration of 2nd gas
  • Increased uptake of 2nd gas to due gradient
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18
Q

Second Gas Effect Graph

A
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19
Q

What (2) type of surgeries are counterindicated with using Second Gas Effect?

A
  1. Closed Space Surgeries (stomache, eyeball, lung, intestines)
  2. Unstable Cardiac patients
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20
Q

Nitrous Oxide transfer depends on (2) factors

A
  • Nitrous diffusing into air filled cavities
  • Magnititude of pressure
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21
Q

How much Nitrous diffuses into airfilled cavities? How quickly?

A
  • up to 10L in 10-15 minutse
  • depends on Compliant walls vs non-compliant walls
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22
Q

Magnitude of pressure of Nitrous depends on….

A
  • partial pressure of nitrous
  • blood flow to cavity
  • duration of nitrous administration.
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23
Q

Nitrous Oxide Transfer Graph

A
  • Open shapes = nitrous inhalation: 300% increase in 1 hour
  • Black Shapes: oxygen inhalation
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24
Q

Name (3) things that can change the speed of induction

A
  1. Increased Alveolar Ventilation
  2. Spontaneous v Mechanical Ventilation
  3. Solubility
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25
Q

How does Increased Alveolar Ventilation change the speed of induction?

A
  • Increased Respiratory rate speeds PA –> PI and induction of anesthesia
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26
Q

Name (1) thing that can slow the speed of induction

A

Decreased PaCO2 (hyperventilation)
* Decreases CBF and limits speed of induction

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27
Q

Induction and Sponataneous Ventilation

A

Negative Feedback Loop
* Dose dependent depressant effects
* As input decreases:
1. Volatile redistribution
2. tissue –> brain w. high concentrations
3. to tissues with low concentrations (fat)
4. As brain concentration decreased, ventilation increases

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28
Q

Induction and Mechanical Ventilation

A
  • body loses the negative feedback loop and is not able to compensate.
  • We have to control the redistribution effects.
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29
Q

Define Solubility

A
  • a ratio of how inhaled anesthestics distribute between 2 compartments at equilibrium
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30
Q

Solubility depends on what (3) Factors

A
  1. Equal partial pressures
  2. relative capacity of each compartment to hold volatile.
  3. Temperature dependent ( ↑temp =↓ solubility)
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31
Q

What happens when the blood solubility is low/high?

A
  • Low: miminal amounts must be dissolved —— Rapid Induction
  • High: large amounts must be dissolved —– Induction prolonged
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32
Q

FA: FI: Solubility Graph

A
  • Halothane: 30 min -> 50% … slowest
  • Iso: 30 min -> 70%
  • Des: 30 min-> 90%: Quickest
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33
Q

What Volatile has the quickest induction than any other drug (normal dosing)?

A
  • Desflurane
34
Q

Methoxyflurane (Blood:Gas Co-eff)

A

12

35
Q

Halothane (Blood: Gas Co-eff)

A

2.54

36
Q

Isoflurane (Blood: Gas Co-eff)

A

1.46

37
Q

Nitrous Oxide (Blood: Gas Co-eff)

A

0.46

38
Q

Desflurane (Blood: Gas Co-eff)

A

0.42

39
Q

Sevofurane (Blood: Gas Co-eff)

A

0.69

40
Q

Name the Volatile Anesthetic that is soluble

A
  1. Methoxyflurane
41
Q

Name the (2) Volatiles that are Intermediately soluble

A
  1. Halothane
  2. Isoflurane
42
Q

Name the (3) Volatiles that are Poorly Soluble

A
  1. Nitrous Oxide
  2. Desflurane
  3. Sevoflurane
43
Q

Name (2) things that can effect Emergence

A
  1. Rate of decrease in Pbr
  2. Depends on length of anesthetics
44
Q

Define rate of decrease in Pbr and give (2) factors

A

Washout from brain….rapid
1. High cardiac output
2. inhaled anesthetic are not highly soluble in brain

45
Q

Name (4) factors than can affect the length of anesthetics

A
  1. When PI is zero (inhaled agents turned off)
  2. Muscle/fat maybe not at equilibrium
  3. muscle/fat continues to take up anesthetics (helps decrease PA and PBr)
  4. Remember VRG
46
Q

Emergence from inhaled anesthetics

A
  • Fat solubility
  • Halothane - 120 mins; no equal alveolar/blood ratio
  • Desflurane - drops quicker, gone in 120 mins
47
Q

Duration of Anesthetic: Recovery Time

A
  • Halothane – longer wake up
  • Desflurane- quicker wake up
48
Q

Minimum Alveolar Concentration (MAC) Definition

A
  • concentration at 1 atm that prevents skeletal muscle movement in response to supramaximal, painful stimulation in 50% of patients.
  • Same as ED50
49
Q

1.3 MAC

A
  • the concentration at 1atm that prevents skeletal muscle movement in response to supramaxiaml, painful stimulation in 99% of patients.
50
Q

MAC (awake) values

A
  • 0.3 -0.5 MAC
  • can open eyes
  • warning of emergence
51
Q

MAC (BAR)

A
  • 1.7 - 2.0
  • blunts automatic reflexes
  • can prevent SNS response
52
Q

Nitrous Oxide MAC

A

104

53
Q

Halothane MAC

A

0.75

54
Q

Isoflurance MAC

A

1.17

55
Q

Desflurance MAC

A

6.6

56
Q

Sevoflurane MAC

A

1.8

57
Q

How much volatile, in terms of MAC, do you have to give someone to keep them asleep?

A
  • 1.3 x MAC
58
Q

Name the (2) biggest factors that alter MAC

A
  • Body temperature
  • Age
59
Q

How much do you adjust your MAC for age? What are does MAC peak?

A
  • 6% each decade (↓ older)
  • Peaks @ 1 year
60
Q

Name (4) things that can increase MAC

A
  1. hyperthermia
  2. Excess pheomelanin production (red heads)
  3. Drug -induced increase in catecholamines
  4. Hypernatremia
61
Q

Name (11) items that can decreased MAC

A
  1. Hypothermia
  2. Preoperative medications, intraoperative opiods
  3. Alpha-2 agonist
  4. Acute alcohol ingestion
  5. Pregnancy
  6. Post-Partum
  7. Lidocaine
  8. PaO2 < 38 mmHg
  9. Mean BP <40 mmHg
  10. Cardiopulmonary ByPass
  11. Hyponatremia
62
Q

Name (8) items that have no change in MAC

A
  • Chronic Alcohol abuse
  • Gender
  • Duration of anesthesia
  • PaCO2 15 - 95 mmHg
  • Blood pressure > 40 mmHg
  • Hyper/hypokalemia
  • Thyroid gland dysfunction
63
Q

Name (3) ways you can cause Spinal Immobility

A
  1. Depress excitatory AMPA and NMDA –> glutamate receptors
  2. Enhance inhibitory glycine receptors –> strychnine, glycine antagonist
  3. Act on sodium channels –> blocks presynaptic release of glutamate.
64
Q

Loss of Consciousness is caused by

A
  1. Inhibitory transmission of GABA –> brain and RAS
  2. Potential of glycine in brainstem
  3. No effect of volatile on AMPA, NMDA, or kainite
65
Q

Volatile Color Container: Yellow

A

Sevoflurane

66
Q

Volatile Container Color: Blue

A

Desflurane

67
Q

Volatile Container Color: Purple

A

Isoflurance

68
Q

Define Partial Pressure

A

A mixture of gases in a closed container exert a pressure on the walls
* 1 part that is any gas
* Sum of the parital pressures (P total = Pgas1 + Pgas2 + Pgas3

** Daltons Law

69
Q

Define Vapor Pressure

A
  • Pressure at which vapor, and liquid are at equilibrium
  • Evaportation = condensation
70
Q

Define Henry’s Law

A
  • Amount of dissolved gas in a liquid is proportional to its partial pressure above the liquid
71
Q

Describe “Overpressurizing”

A
  • Henry’s Law
  • Increases anesthetic depth
  • if partial pressure of gas doubles, it doubles the molecules hitting liquid surface.
72
Q

Consequences of heating/cooling vapor pressure

A
  • Heat: increases vapor pressure
  • Cool: Decreases vapor pressure
73
Q

High vapor pressure are considered more ____________ and are more likely to ___________.

A
  • volatile
  • evaporate
74
Q

Halothane Vapor Pressure

A

243 torre

75
Q

Isoflurane Vapor Pressure

A

238 torre

76
Q

Desflurane Vapor Pressure

A

669 torre

77
Q

Sevoflurane Vapor Pressure

A

157 torr

78
Q

Name 3 jobs of the Vaporizer

A
  • Changes liquid to Vapor
  • Add an amount of vapor to fresh gas flow
  • Partial pressure/total pressure = Volume %
79
Q

Vaporizer: Variable bypass

A
  • Dilute saturate vapor
  • splitting ratio
80
Q

Vaporizer: Flow-over (Wicks)

A
  • increases gas-liquid interface
  • Improves efficiency of vaporization

Pharmacology Exam 3 (4 decks)

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