SS25 3-3 Inhaled Anesthetics Part 1 (Exam 3) Flashcards
(98 cards)
1
Q
What are the pharmacokinetics of inhaled anesthetics?
UDME
A
- Uptake from alveoli into pulm capillary blood
- Distribution
- Metabolism
- Elimination via lungs
2
Q
What non-modifiable risk factor influences the pharmacokinetics of Volatiles?
- How?
A
Age
↓ lean body mass ↑ fat ↑ VD for drugs (esp. fat soluble) ↓ CL if pulmonary exchange is impaired ↑ time constraints d/t low CO
3
Q
Are volatiles lipid soluble or fat soluble?
A
- Fat/lipid soluble
4
Q
What is significant about volatiles being delivered via inhalant?
A
- Respiratory status plays a direct role in uptake and elimination
5
Q
What is Boyle’s Law?
Clinical significance?
A
- At a constant temperature, pressure and volume of gas are inversely proportional (↑P = ↓V & vice versa)
- PPV begins → Bellows contract & become more compact → ↑circuit & vent pressure → gases flow from high pressure circuit to low pressure lungs
6
Q
In relation to volatiles, what’s Fick’s Diffusion Law?
A
Once air molecules of vapor & O₂ enter alveoli, they move around freely and begin to diffuse into the pulmonary capillaries to then get to brain
Brain = main effector/ receptor site
7
Q
Diffusion depends on:
A
- Partial pressure gradient of the gas (Air, N2O, Sevo, etc.)
- Solubility of the gas (things that are more diffusable get across capillary easier)
- Thickness of the membrane (thicker = hard to cross)
STP
8
Q
What is Graham’s Law of Effusion?
A
- Process by which molecules diffuse through pores and channels without colliding
- Process of molecules getting to capillary membrane dependant on solubility
9
Q
Smaller molecules effuse faster depending on (_______).
A
- Solubility (diffusion)
10
Q
Which diffuses faster CO₂ or O₂? Why?
A
- Despite O₂ weighing less,
- **CO₂ diffuses into gas filled spaces 20x faster due to higher solubility **
Molecular wt: CO 44 g & O₂ 32 g
11
Q
Examples of places in the body that are air-filled.
A
- lungs
- gut
- ear & inner ear
12
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
13
Q
PA and Pa relationship
A
- Pressure in alveoli can go back and forth from lung capillary (lung artery)
14
Q
Pa and PBr relationship
A
Pressure in lung can equilibrate with the brain
15
Q
How can you determine the Alveolar pressure (PA)?
A
- Measure end-tidal exhaled gas
Ie: ETDes, ETSevo, etc.
Hard to measure pressure in lung artery or brain
16
Q
Alveolar pressure (PA) is an indicator of:
A
- Depth of anesthesia
- Recovery from anesthesia
- able to determine what stage of GA their at
17
Q
If PBr > PA then what do we expect to be occurring?
- Why?
A
- The patient should be waking up
- This means the exhaled gas > than the inhaled gas and the concentration gradient is moving towards the alveoli away from the brain.
18
Q
What input factors affect the diffusion of volatile gasses getting from the anesthetic machine to the alveoli?
A
- Inspired partial pressure (how much gas are you getting?)
- Alveolar ventilation (how fast are you brathing?)
- Anesthetic system re-breathing (less rebreathing means more gas to patient)
- FRC
IARF =** Input Alveolar Anesthesia Factors**
19
Q
Which factors affect the uptake of anesthetic gas from the alveoli to the blood?
A
- Blood:gas partition coefficient
- Cardiac output
- Alveolar-venous pressure difference
20
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
21
Q
What factors affect the uptake of anesthetic gas from the arterial blood to the brain?
A
- Blood:Brain partition coefficient
- Cerebral blood flow
- arterial-venous partial pressure difference
22
Q
Gas goes from a ____ gradient to a ____ gradient in order to reach a steady state.
A
high; low
23
Q
What does PI mean?
A
Partial pressure of inspired volatile gas.
24
Q
How can gas be “forced” to the brain quicker?
A
By increasing PI. This creates a higher gradient for the gas to flow from PA → Pa → PBrain
25
What does FE/FI mean?
FE/FI is the ratio of expired gas to inspired gas.
26
What concept is this chart conveying?
Concentration Effect: essentially, ↑concentration inspired gas = ↑PA = increased rate of diffusion
The more concentrated inspired gasses (85%) can get closer to the FE/FI equillibrium the fastest.
Less concentrated inspired gasses will take longer to reach equillibrium.
FE/FI equillibrium can never be reached by inhaled anesthetics though, but they can get close.
27
What is over-pressurization?
- A large increase in PI so as to force gas from PA → Pa → PBrain much faster.
28
What would sustained delivery of over-pressurization result in?
Overdose
29
1 _______ breath of an inhaled anesthetic should cause ________.
Vital capacity breath
loss of eyelash reflex
30
What type of inductions mostly use overpressurization?
Inhaled inductions
31
What gas does the second gas effect always apply to?
N₂O (nitrous oxide)
32
What is the second gas effect as it relates to anesthesia?
- Uptake of **N₂O accelerates a concurrently administered volatile gas**.
33
How does N₂O create the second gas effect?
N₂O hyper-concentrates volatiles to create a high concentration gradient by being super-diffusible.
34
Describe what is being depicted on the graph below.
Halothane uptake is faster when 70% N₂O is used compared to 10% N₂O
This demonstates the Second Gas Effect, where the rapid uptake of N₂O enhances the concentration of the second gas (halothane)
35
What cases would nitrous oxide **not** be utilized in?
Why?
- 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).
36
What specific cases are bad for the usage of N₂O?
- Ear & eye
- Open belly
- Lung
The ear has low distensibility because it has a lot of rigid bones, the high pressures in the ear can cause damage
37
What factors affect the degree of pressure N₂O would exert on a cavity that it filled?
- Partial pressure of N₂O
- Blood flow to the cavity
- Duration of N₂O administration
38
What would nitrous inhalation in a patient with pneumothorax do?
Expand the pneumothorax
39
What could N₂O on an intraocular case do?
- Massively increase retinal artery pressure and cause permanent vision loss.
This can happen if the patient is on nitrous for only an hour!
40
How much nitrous in liters (L) can in the 1st 10-15 minutes of administration?
10L
41
Decreased ______ from hyperventilation will decrease cerebral blood flow and limit induction speed.
PaCO₂
42
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).
43
If the temperature of blood increases then solubility ______.
decreases
44
What does a low blood solubility mean for induction?
Less gas has to be dissolved = PA → Pa is rapid = rapid induction.
45
What does a high blood solubility mean for induction?
More gas has to be dissolved = PA → Pa is slow = slow induction.
46
What is being described in the graph below?
How quickly the inspired concentration of a gas equals the alveolar concentration of said gas.
47
What volatile gasses are intermediately soluble?
**H**alothane
**E**nflurane
**I**soflurane
48
What is the blood:gas partition coefficient of halothane?
Halothane = 2.54
49
What is the blood:gas partition coefficient of enflurane?
Enflurane = 1.90
50
What is the blood:gas partition coefficient of Isoflurane?
Isoflurane = 1.46
51
What volatile gasses are poorly soluble?
- N₂O
- Desflurane
- Sevoflurane
52
What is the blood:gas partition coefficient of N₂O?
Nitrous = 0.46
53
What is the blood:gas partition coefficient of Desflurane?
Desflurane = 0.42
54
What is the blood:gas partition coefficient of Sevoflurane?
Sevoflurane = 0.69
55
What are the blood:gas solubilities of all the gasses we have to know for anesthesia pharm?
56
Emergence is the rate of decrease where?
When does emergence happen?
PBrain
When is PI zero
57
What does emergence depend on?
The length of the anesthetic
58
What occurs (in regards to our partial pressure gradients) during emergence from anesthesia?
Concentration gradient reverses.
PA ← Pa ← PBrain
59
What helps decrease concentration of volatile anesthetic in PA and PBrain on emergence?
Continued uptake by Muscle/Fat if not already at equilibrium.
60
What color coding does isoflurane have?
Purple
61
What color coding does sevoflurane have?
Yellow
62
What color coding does desflurane have?
Blue
63
Which anesthetic would you anticipate as having the quickest recovery?
Slowest?
Fastest recovery = desflurane
Slowest recovery = halothane
64
What is 1 MAC?
Concentration at 1atm that prevents skeletal muscle movement in response to supramaximal, painful stimulation in 50% of patients.
65
What is 1.3 MAC?
Concentration at 1atm that prevents skeletal muscle movement in response to surgical stimulation in 99% of patients.
66
What would ED99 be equivalent to in regards to MAC?
ED99 ≈ 1.3 MAC
67
What is MACawake?
0.3 - 0.5 MAC: partial awakeness and responsiveness.
68
What is MACBAR?
1.7 - 2.0 MAC: Blunts autonomic responses. No SNS response at all, essentially an overdose.
69
What patient are standardized MAC values based on?
30 - 55 y/o at 37°C at 1atm
70
What is the MAC of N₂O?
What does this mean?
N₂O MAC = 104%. Can't be used as sole anesthetic agent.
71
What is the MAC of Halothane?
0.75%
72
What is the MAC of Enflurane?
1.63%
73
What is the MAC of Isoflurane?
1.17%
74
What is the MAC of Desflurane?
6.6
75
What is the MAC of Sevoflurane?
1.8%
76
What are the two biggest factors that affect MAC?
- Body temperature
- Age
77
At what age does MAC peak?
1 y/o
78
How much does MAC need decrease as one gets older?
6% per decade.
79
What factors will increase MAC?
- Hyperthermia
- Excess Pheomelanin (redheads)
- Drug-induced ↑ catecholamines
- Hypernatremia
80
What factors will decrease MAC?
*Extensive list*
**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
81
How does loss of consciousness occur with the use of volatile anesthetics?
- Potentiation of GABAA in the brain.
- Potentiation of glycine in the brainstem.
82
Which of these two liquids in enclosed containers has the higher vapor pressure?
Liquid B: more evaporative.
*Vapor pressure is the pressure at which vapor and liquid are at equilibirum.*
83
What is Dalton's law?
- The sum of all partial pressures will equal the total pressure.
- Ptotal = Pgas1 + Pgas2...
84
What is Henry's Law?
The amount of dissolved gas in a liquid is proportional to its partial pressure above the liquid.
85
What does Henry's law mean in practice?
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.**
86
Heat will _____ vapor pressure.
increase
87
Cold temperatures will _____ vapor pressure.
decrease.
88
A lower vapor pressure gas is inherently more volatile. T/F ?
False. ↑vapor pressure = ↑volatility
89
What is the vapor pressure of halothane?
243
90
What is the vapor pressure of Enflurane?
175
91
What is the vapor pressure of Isoflurane?
238 torr (mmHg)
92
What is the vapor pressure of Desflurane?
669 torr
93
94
What is the vapor pressure of Sevoflurane?
157 torr (or mmHg)
95
96
What is the variable bypass on the anesthetic machine?
A way to dilute/concentrate the amount of anesthetic gas reaching the patient.
97
What is the splitting ratio?
How much gas is being sent into the vaporizer
98
What is the purpose of the wicks found in the vaporizing chamber below?
The wicks increase gas-liquid interface and **improve vaporization**.
