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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
How does Increased Alveolar Ventilation change the speed of induction?
* Increased Respiratory rate speeds PA --> PI and induction of anesthesia
26
Name (1) thing that can slow the speed of induction
Decreased PaCO2 (hyperventilation) * Decreases CBF and limits speed of induction
27
Induction and Sponataneous Ventilation
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
28
Induction and Mechanical Ventilation
* body loses the negative feedback loop and is not able to compensate. * We have to control the redistribution effects.
29
Define Solubility
* a ratio of how inhaled anesthestics distribute between 2 compartments at equilibrium
30
Solubility depends on what (3) Factors
1. Equal partial pressures 2. relative capacity of each compartment to hold volatile. 3. Temperature dependent ( ↑temp =↓ solubility)
31
What happens when the blood solubility is low/high?
* Low: miminal amounts must be dissolved ------ Rapid Induction * High: large amounts must be dissolved ----- Induction prolonged
32
FA: FI: Solubility Graph
* Halothane: 30 min -> 50% ... slowest * Iso: 30 min -> 70% * Des: 30 min-> 90%: Quickest
33
What Volatile has the quickest induction than any other drug (normal dosing)?
* Desflurane
34
Methoxyflurane (Blood:Gas Co-eff)
12
35
Halothane (Blood: Gas Co-eff)
2.54
36
Isoflurane (Blood: Gas Co-eff)
1.46
37
Nitrous Oxide (Blood: Gas Co-eff)
0.46
38
Desflurane (Blood: Gas Co-eff)
0.42
39
Sevofurane (Blood: Gas Co-eff)
0.69
40
Name the Volatile Anesthetic that is soluble
1. Methoxyflurane
41
Name the (2) Volatiles that are Intermediately soluble
1. Halothane 2. Isoflurane
42
Name the (3) Volatiles that are Poorly Soluble
1. Nitrous Oxide 2. Desflurane 3. Sevoflurane
43
Name (2) things that can effect Emergence
1. Rate of decrease in Pbr 2. Depends on length of anesthetics
44
Define rate of decrease in Pbr and give (2) factors
Washout from brain....rapid 1. High cardiac output 2. inhaled anesthetic are not highly soluble in brain
45
Name (4) factors than can affect the length of anesthetics
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
Emergence from inhaled anesthetics
* Fat solubility * Halothane - 120 mins; no equal alveolar/blood ratio * Desflurane - drops quicker, gone in 120 mins
47
Duration of Anesthetic: Recovery Time
* Halothane -- longer wake up * Desflurane- quicker wake up
48
Minimum Alveolar Concentration (MAC) Definition
* concentration at 1 atm that prevents skeletal muscle movement in response to supramaximal, painful stimulation in 50% of patients. * Same as ED50
49
1.3 MAC
* the concentration at 1atm that prevents skeletal muscle movement in response to supramaxiaml, painful stimulation in 99% of patients.
50
MAC (awake) values
* 0.3 -0.5 MAC * can open eyes * warning of emergence
51
MAC (BAR)
* 1.7 - 2.0 * blunts automatic reflexes * can prevent SNS response
52
Nitrous Oxide MAC
104
53
Halothane MAC
0.75
54
Isoflurance MAC
1.17
55
Desflurance MAC
6.6
56
Sevoflurane MAC
1.8
57
How much volatile, in terms of MAC, do you have to give someone to keep them asleep?
* 1.3 x MAC
58
Name the (2) biggest factors that alter MAC
* Body temperature * Age
59
How much do you adjust your MAC for age? What are does MAC peak?
* 6% each decade (↓ older) * Peaks @ 1 year
60
Name (4) things that can increase MAC
1. hyperthermia 2. Excess pheomelanin production (red heads) 3. Drug -induced increase in catecholamines 4. Hypernatremia
61
Name (11) items that can decreased MAC
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 9. Cardiopulmonary ByPass 10. Hyponatremia
62
Name (8) items that have no change in MAC
* Chronic Alcohol abuse * Gender * Duration of anesthesia * PaCO2 15 - 95 mmHg * Blood pressure > 40 mmHg * Hyper/hypokalemia * Thyroid gland dysfunction
63
Name (3) ways you can cause Spinal Immobility
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
Loss of Consciousness is caused by
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
Volatile Color Container: Yellow
Sevoflurane
66
Volatile Container Color: Blue
Desflurane
67
Volatile Container Color: Purple
Isoflurance
68
Define Partial Pressure
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
Define Vapor Pressure
* Pressure at which vapor, and liquid are at equilibrium * Evaportation = condensation
70
Define Henry's Law
* Amount of dissolved gas in a liquid is proportional to its partial pressure above the liquid
71
Describe "Overpressurizing"
* Henry's Law * Increases anesthetic depth * if partial pressure of gas doubles, it doubles the molecules hitting liquid surface.
72
Consequences of heating/cooling vapor pressure
* Heat: increases vapor pressure * Cool: Decreases vapor pressure
73
High vapor pressure are considered more ____________ and are more likely to ___________.
* volatile * evaporate
74
Halothane Vapor Pressure
243 torre
75
Isoflurane Vapor Pressure
238 torre
76
Desflurane Vapor Pressure
669 torre
77
Sevoflurane Vapor Pressure
157 torr
78
Name 3 jobs of the Vaporizer
* Changes liquid to Vapor * Add an amount of vapor to fresh gas flow * Partial pressure/total pressure = Volume %
79
Vaporizer: Variable bypass
* Dilute saturate vapor * splitting ratio
80
Vaporizer: Flow-over (Wicks)
* increases gas-liquid interface * Improves efficiency of vaporization

Pharmacology Exam 3 (4 decks)

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