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Anesthesia Pharm (Spring '24) - B > Lecture 11 (Exam 3) Inhaled Anesthetics > Flashcards

Lecture 11 (Exam 3) Inhaled Anesthetics Flashcards

1
Q

What gas does a blue gas tank contain?

A

Nitrous
This will also show up blue on your monitor.

Side note: Oxygen tanks are always green and usually show up as green on your monitor.

(Dr Kane)

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2
Q

T/F:
The machines in the OR know what gas you turn on because they are calibrated. Each gas has its own color that will populate with its numbers on the monitor to the far right when you turn it on.

A

True!
3rd column:
Blue = Desflorane
Yellow = Sevoflorane
Purple = Isoflorane

(Dr Kane)

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3
Q

Look at the pink square!
Now tell me, what does the top line indicate? (88-0-6.0)
What does the bottom line indicate? (93-0-6.8)

A

The top line indicates the end tidal and the percent of gas(s) you are breathing out!
The bottom line indicates your inhaled tidal and the percent of gas(s) you are breathing in!

(Slide 43 & Dr Kane)

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4
Q

What is the “splitting ratio”?

A

It is the amount of air allowed to pass into the volatile gas chamber. The bigger the hole in the splitting valve, the more anesthetic gas you are going to pick up!
(Slide 44)

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5
Q

What controls the splitting valve/splitting ratio?

A

Control dial!
(Slide 44)

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6
Q

if the control dial is closed are you going to deliver any volatile gases to your patient?

A

No!
(Slide 44)

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7
Q

How did they improve the anesthetic gas chamber to be able to pick up MORE anesthetic gas molecules without having to give MORE carrier gas?

A

They added wicks!
(Slide 44)

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8
Q

List the common inhaled anesthetics from fastest onset/offset to slowest onset/offset

A

Desflurane > Sevoflurane > Isoflurane
Slide 21

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9
Q

Which volatile anesthetic is the gold standard, but is no longer used?

A

Halothane
Slide 21

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10
Q

What is the blood:gas partition coefficient of Halothane?

A

B:G Kpc= 2.54

Pv= 243

MAC= 0.75

Slide 22

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11
Q

What is the blood:gas partition coefficient of Enflurane?

A

B:G Kpc= 1.90

Pv= 175
Slide 22

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12
Q

What is the blood:gas partition coefficient of Isoflurane?

A

1.46

Pv= 238

MAC= 1.17

Slide 22

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13
Q

What is the blood:gas partition coefficient of Nitrous oxide?

A

0.46

MAC= 104
Slide 22

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14
Q

What is the blood:gas partition coefficient of Desflurane?

A

0.42

Pv= 669

MAC= 6.6

Slide 22

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15
Q

What is the blood:gas partition coefficient of Sevoflurane?

A

0.69 *sexy sevo

Pv= 157

MAC= 1.8

Slide 22

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16
Q

If a drug has a low blood:gas partition coefficient does it want to stay in the blood or leave and go to the alveoli?

A

It wants to leave the blood - There will be a faster onset/offset
Slide 22

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17
Q

If the amount of volatile in the brain __________ patients wake up

A

Decreases
Slide 24

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18
Q

Timing of turning off your inhaled anesthetic is based on…

A

Its solubility
Slide 24

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19
Q

It takes the gas longer to be eliminated if the solubility is…

A

Higher

Slide 25

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20
Q

Name the following volatile anesthetic’s vapor pressures in units of torr:

  • Desflurane (Suprane)
  • Halothane:
  • Isoflurane (Forane):
  • Sevoflurane (Ultane):
A

Desflurane (Suprane): 669
Halothane (Fluothane): 243
Isoflurane (Forane): 238
Enflurane (Ethrane): 175
Sevoflurane (Ultane): 157

(“Dolphins Have Incredible Echolocation Skills” –> Dolphin made me think of water/vapor) 🐬
slide 42

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21
Q

Partial Pressure: in a mixture of gases in a closed container, each gas exerts pressure on the walls.

Example problem
0.4 atm of O2, 0.3 atm of NO2, and 0.3 of Sevo occupy a container in the anesthesia gas circuit at one given time with a constant temperature.
What is the total pressure?

A

Dalton’s Law
Pgas1 + Pgas2 + Pgas3 … = Total pressure

Therefore, the total pressure of the 3 given partial pressures = 1.0 atm

(slide 38)

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22
Q

Looking inside our anesthesia circuit, we know that the volatile anesthetic is in gas and liquid form, and it’s the _______ gas that picks up the ___ form of the anesthetic and carries it through the circuit to the alveolus.

What are our 3 carrier gases?
What is the right-most gas?
Why is it designed that way?

A

carrier gas that picks up the gas form

Air, Nitrous, Oxygen

Right-most gas is O2

Designed that way to prevent leak of oxygen gas. This way, you’re less likely to be left with an empty O2 tank in the middle of a case if a gas leak occurs.

(slide 39)

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23
Q

Define Vapor Pressure per the lecture slide.

A

Pressure at which vapor and liquid are at equilibrium

Where evaporation and condensation are equal

(slide 39)

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24
Q

“The amount of dissolved gas in a liquid is proportional to its partial pressure above the liquid” is known as _______ law?

What does this law essentially describe for us as anesthetists?

What else does this mean?

A

Henry’s Law - “The amount of dissolved gas in a liquid is proportional to its partial pressure above the liquid”

“Overpressurizing” - if the partial pressure of gas doubles, then double the molecules hit the liquid surface ⬆️ anesthetic depth; increasing our partial pressure of anesthetic

(slide 40)

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25
Q

____ increases vapor pressure
____ decreases vapor pressure

What does it mean if one particular gas has more vapor pressure?

A

Heat increases 🔥
Cold decreases 🧊

More volatile! Also means the gas is more likely to evaporate (think desflurane)

(slide 41)

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26
Q

Which of our volatiles has the highest and lowest vapor pressure?

A

highest = Desflurane (669 torr)
lowest = Sevoflurane (157 torr)

(Dolphins Have Incredible Echolocation Skillz) 🐬

Fun fact: when you dumped that bottle of desflurane out to see how fast it evaporated, you just released the same amount of greenhouse gases as if you had burned nearly 1000 pounds of coal. Something to think about. <– did Grayson tell you that? <– 👀 lol

(slide 42)

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27
Q

What decreases MAC requirements?

A

Hypothermia (low metabolic requirements) 🥶
Preoperative medication, intraoperative opioids💊
Alpha-2 agonists (cause sedation –> precedex, clonidine)
Acute alcoholism ingestion 🍸
Pregnancy 🤰
Postpartum (early 12-72 hours)
Lidocaine
PaO2 <38mmHg
MAP <40mmHg (they are barely alive)
Cardiopulmonary bypass
Hyponatremia (without Na we are not depolarizing much per Dr. Kane)

Slide 32

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28
Q

What are the things that do not change MAC?

A
  • Chronic alcohol abuse
  • Weight!
  • Gender ⚤
  • Duration of anesthesia
  • PaCO2 15-95 mmHg
  • PaO2 >38 mmHg
  • MAP >40mmHg
  • Hyper/Hypokalemia
  • Thyroid dysfunction

Slide 33

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29
Q

How does Volatile anesthetic (VA) work on spinal immobility?

A
  • ↓Depress excitatory AMPA and NMDA (glutamate receptors).
  • ↑ Enhance inhibitory glycine RECEPTORS
  • Act on sodium channels (blocks presynaptic release of glutamate)

(It does not cause paralysis; It’s mediated muscle relaxation. )
Slide 35

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30
Q

How does VA work on sodium channels?

A

VA interacts with subtypes of sodium channels expressed at the presynaptic junction, which block the release of glutamate.
Slide 35

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31
Q

How does VA cause loss of consciousness in brain?

A
  • Augments inhibitory transmission of GABA in the brain,
    especially RAS (regulates wakefulness and sleep cycle)
  • Potentiates glycine activation in brainstem.
  • No effect of volatiles on AMPA, NMDA or Kainate in brain

Slide 36

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32
Q

How do we administer Volatile Anesthetics?

A

Through Vaporizers.
(Refill vaporizers as you need)
Slide 37

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33
Q

How do you know if VA is running low in vaporizers?

A

There is a little window in each vaporizer that indicates the level of VA. You can see the liquid level through this window.
(some machines can also tell you that your VA is running out)
Slide 37

34
Q

You filled your VA in the vaporizer but realized that your patient woke up in the middle of the procedure. Why did this happen?

A

Dumb butt! You forgot to turn on the vaporizer!
Make sure you always turn on the vaporizer after you refill.
Slide 37

35
Q

What is the ‘last’ step of induction/phase 2 of anesthesia?

Doing this starts what phase of anesthesia?

A

Turn on the vaporizer! (the inhaled anesthetic/volatile)

This begins phase 3 or MAINTENANCE!

Slide 1

36
Q

Could you sedate someone (adult or child) without an IV?

A

YES! With your V.A.
It’s called “breathing down”. This is common practice for children 👶🏻 (start IV after they are down)

*can be as fast at 3 breaths
*can do this if IV infiltrates for adults

Slide 1

37
Q

What factors influences the pharmacokinetics of VA?

A
  • Influenced by aging (elder)
  • ⬇️ muscle mass
  • ⬆ fat (⬆ Vd for drugs - esp if they are more lipid soluble)
  • CO
  • pulmonary disease (impairs gas exchange)

Slide 3

38
Q

Define Boyle’s Law.

A

At a constant temperature, pressure and volume of a gas are INVERSELY proportional.

Slide 4

39
Q

Why do we care about Boyle’s law in anesthesia?

A

Remember the pistons from Dr. Rich?! Well, those are basically our anesthesia ventilator bellows…
The build up of pressure causes gas to flow from high pressure to low pressure.

Also gas diffusion: higher pressures in the alveoli will cause a shift of gas into the blood (less pressure)

Slide 4

40
Q

Once the gas molecules get to the alveoli, they bounce around randomly and begin to diffuse into the capillary.

Diffusion depends on ___ ___ ___ of the gas, _____ of the gas and _____ of the membrane it’s up against.

This describes which law?

A

partial pressure gradient, solubility of the gas, thickness of the membrane

Fick’s Diffusion Law

Slide 5

41
Q

What is one exception we learned in lecture (two substances we deal with a lot) to Graham’s Law? and why?

A

CO2 & O2 –> CO2 is more diffusible bc of its solubility!

Slide 6

42
Q

The smaller the molecule, the ______ the effusion.

The process by which molecules diffuse through pores and channels without colliding describes which law?

A

smaller = faster the effusion

Graham’s Law of Effusion
I like to remember that graham crackers have holes (or pores)

Slide 6

43
Q

What are 3 partial pressure gradients we are concerned about when administering a volatile anesthetic?

A
  1. Anesthesia machine to alveoli.
  2. Alveoli to blood.
  3. Arterial blood to brain.
    (Slide 8)
44
Q

What affects the pressure gradient from the anesthetic machine to alveoli? (4 things)

A
  1. Inhaled partial pressure
  2. Alveolar ventilation
  3. The anesthesia breathing system
  4. Functional residual capacity.

Basically, the PI (Inhaled partial pressure, gas delivery) has to be able to overcome the PA (alveolar pressure) for the anesthetic gas to be able to get into the alveoli. (Slide 8)

45
Q

What factors contribute to the partial pressure gradients found in the alveoli to blood? (3 things)

A
  1. Blood: gas coefficient
  2. CO
  3. Alveolar to venous partial pressure difference

The anesthetic gas is now in the alveolar space (PA) and must overcome the pressure in the pulmonary capillaries (Pa) to be able to diffuse into the blood. The concentration of the gas in the blood vs the alveolar space, how fast or slow CO is, and the pressure differences between the alveoli and blood all contribute to the overall gradient here. (Slide 8)

46
Q

What factors affect the partial pressure gradient of the arterial blood to the brain? (3)

A
  1. Brain:blood partition coefficient
  2. Cerebral blood flow
  3. Arterial to venous partial pressure difference

(Slide 8)

47
Q

What is the concentration effect?

A

The higher the PI (inspiratory), the more rapidly the PA approaches the PI. This will offset uptake of gas into Pa. Basically, higher delivery of gas = faster time to go to sleep.

The higher the inspiratory pressure of what I’m breathing, the faster the alveolar pressure will rise and reduce that pressure difference gradient between PI and PA as gas is being up-taken into capillaries. (achieving equilibrium between the PI and PA as gas keeps being taken away into blood).

The partial pressure of the gas has to be higher in order to offset the intake of the gas in the alveoli, therefore the gas is able to reach its ideal sites in the brain faster. (Slide 10)

48
Q

What anesthetic will get you to sleep faster - a gas with a concentration of 85% anesthetic or the gas with a concentration of 10% anesthetic?

A

The 85% concentrated gas gets you to sleep faster! This is due to the concentration effect. (Slide 11)

49
Q

What is overpressurization?

A

A very very large increase in PI. One heaping southern helping dose of an anesthetic, which will get you to sleep a few breaths. (Slide 12)

50
Q

What is a high concentration of sevoflurane? How many breaths will it take a high concentration of sevoflurane to get you to lose your eyelash reflex?

A

Sevoflurane of 7% = high concentration. 1 vital capacity breath at this dose will get you to lose your eyelash reflex. (Slide 12)

51
Q

What is the 2nd gas effect? Which of our gases are ALWAYS used in the 2nd gas effect?

A

The 2nd gas effect is taking a high volume of very soluble gas and delivering it with your anesthetic gas. The rapid uptake of the high volume gas accelerates the rate of uptake of the 2nd gas by helping to concentrate the 2nd gas. The concentration gradient increases for the 2nd gas, making it more likely to diffuse.

We always use nitrous (N2O) as our high volume/high solubility gas. The 2nd gas is our choice of anesthetic. (Slide 13, pg 104 in Stoetling pharm book)

ChatGPT:

Yes, the second gas effect works in part because of increased partial pressures of the second gas in the lungs. Here’s a simplified explanation:

  1. Rapid Uptake of the First Gas: When a large volume of a first gas (often a nitrous oxide, which is a fast-acting anesthetic gas) is absorbed rapidly into the blood from the lungs, it reduces the volume of gas remaining in the lungs.
  2. Creation of a Vacuum Effect: This rapid uptake effectively creates a “vacuum” or a reduction in pressure within the lungs, which increases the rate at which the lungs take in more gas from the anesthesia breathing circuit.
  3. Increased Partial Pressure of the Second Gas: As a result, the concentration and partial pressure of any remaining gases in the lungs, including the second gas (which could be oxygen or another anesthetic gas), temporarily increase. This increase in partial pressure of the second gas in the lungs drives more of it into the blood.
  4. Enhanced Uptake of the Second Gas: Because gases move from areas of higher partial pressure to areas of lower partial pressure (in this case, from the lungs into the blood), the increased partial pressure of the second gas in the lungs leads to its faster and more efficient absorption into the bloodstream.

So, in essence, the rapid absorption of the first gas enhances the uptake of the second gas due to the temporary increase in its partial pressure in the lungs, allowing the second gas to enter the bloodstream more quickly than it would under normal circumstances.

52
Q

With insoluble gases, recovery time is faster or slower?

A

Faster
Slide 26

53
Q

The definition of minimum alveolar concentration (MAC) is

A

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

1 MAC = 1 atm

Same as ED50

Slide 27

54
Q

What level of MAC gives us the desired effect in 99% of patients.

A

1.3 MAC

Slide 27

55
Q

At what level of gas-only anesthetic do we start to get responsiveness?

A

(MAC awake) 0.3-0.5 MAC

Slide 28

56
Q

What level of MAC creates a lack of sympathetic response to stimuli (intubation). ?

A

Mac BAR (Blunt Autonomic Responses. 1.7-2.0 MAC)

We do not use this level of MAC. It would probably make the patient hypotensive and unstable.

Blunts about all sympathetic nervous responses.

Slide 28

57
Q

What is very important to NOT do if the patient was at 0.3-0.5 MAC?

A

IGNORE THE PATIENT!

Slide 28
Dr. Kane

58
Q

MAC value of Nitrous Oxide

A

104%

Slide 29

59
Q

MAC value of Halothane

A

0.75%

Slide 29

60
Q

MAC value of Isoflurane

A

1.17%

Slide 29

61
Q

MAC value of Desflurane

A

6.6%

Slide 29

62
Q

MAC value of Sevoflurane

A

1.8%

Slide 29

63
Q

Factors that alter MAC

A

Body Temp
Age (6% change per decade after 50 [decrease] and under 30 [increase])
MAC peaks at 1 years of age.

Slide 30

64
Q

Factors that INCREASE MAC

A

Hyperthermia

Excess pheomelanin production (red-heads)

Drug-induced increase in catecholamine levels (increased metabolism)

Hypernatremia

Slide 31

65
Q

Nitrous Oxide diffuses into air-filled cavities. How much over how long can this happen with this gas?

A

Up to 10L in the first 10-15 min

(slide 15)

66
Q

Since Nitrous Oxide prefers to diffuse into air-filled cavities, this gas can be contraindicated to give during certain surgeries.
- What is an example if a Compliant-walled organ/surgery we would NOT give Nitrous in.
- What is an example of a Non-compliant wall organ/surgery?
- And Why?

A
  • compliant wall: Bowel surgeries- during a procedure that requires the bowel to be removed from the cavity ex: laparotomy. (because the bowel will expand and not be able to fit back into the abdomen.
  • non compliant wall: inner ear or eye cases. (because these organs are surrounded by bones that does not allow for expansion. This will cause immense pressure to build up.
    (ex: during a retinal repair after receiving 1hr of nitrous a pt recieved retinal artery vision loss due to the pressure that built up during sx making it ischemic)

(slide 15, 16)

67
Q

What are a few air-filled cavities where Nitrous Oxide prefers to diffuse in that Dr. Kane discussed?

A

Inner ear, Bowel, Chest, Lungs

(slide 15)

68
Q

What are 3 factors that determines the magnitude of pressure caused by the administration and diffusion of Nitrous Oxide?

A
  1. The partial pressure of nitrous
  2. Blood flow to cavity
  3. Duration of nitrous administration

(slide 15)

69
Q

What lung diagnosis would cause a contraindication to administer Nitrous Oxygen gas (due to its high diffusibility into air filled cavities)?

A

Pneumothorax (there was a 250% increase in pressure of the pneumo after the pt received nitrous)

(slide 16)

70
Q

Nitrous isn’t always bad, so when is it good to use Nitrous?

A
  • When it is used as a second gas effect to another inhaled anesthetic when we have to go to sleep
  • When the pt cannot tolerate other volatile anesthetics. (nitrous has some analgesic properties)

(slide 16)

71
Q

How can you increase your alveolar ventilation?
By doing this, what would the results be towards inhaled gases?

A

Like with Higher PI, Increased RR speeds PA towards PI - induction of anesthesia

This will result in hyperventilation, which will decrease CBF and CO2 is a vasodilator and decrease respiratory rate (because body wants to decrease rate of loss of CO2)
PA = Pa = PBr

(slide 18)

72
Q
  • By increasing your RR and depth of alveolar ventilation (hyperventilation), what does this do to our PaCO2?
  • In turn to this change in PaCO2, what is our brain’s compensatory mechanism?
  • What does this mean for our gas molecules?
A
  • Will lower our PaCO2 - this will result in decreased CO and vasoconstriction as a means to maintain pressure reducing CBF
  • since there is not as much gas returning to brain b/c decreased CO
  • As brain concentration decreased, there be a return in ventilation - breathing faster and in return will bring more gas to the brain to make it fall asleep again. It is a loop, but it occurs too fast we can’t see it.

(slide 18)

73
Q

The effects of Spontaneous ventilation in regards to alveolar ventilation is a negative feedback loop. How does the body cope as input decreases due to decreased ventilation with volatiles?

A

Alveolar ventilation negative feedback loop is dose dependent depressed
As gas input decreases d/t decreased ventilation:
Volatiles are redistributed. From: tissues with high concentrations (brain) To: tissues with low concentration (fat)
Causing the brain concentration to decrease which in turn increases ventilation.

(slide 19)

74
Q

With our body’s negative feedback loop on alveolar ventilation, would this mechanism be the same with mechanical ventilation as it is with spontaneous ventilation?
And why?

A

NO! Ventilator prevents the body to negative feedback due to its set rate/pressure being given by the machine.
(The body cannot compensate whether the CO2 is going up or down, or whether the molecules are too many or too few, or whether your brain is going more to sleep or less asleep by normal adjustments in RR and depth.)

(slide 19)

75
Q

Define Solubility:

A

A ratio of how the inhaled anesthetic distributes between 2 compartments at equilibrium.
(when partial pressures are equal)

(slide 20)

76
Q

When blood solubility of a gas is low, what are the effects?

A

Minimal amounts must be dissolved; PA/Pa is rapid; induction is rapid
(so: the drug wants to leave the blood and diffuse= goes to brain and goes to sleep faster!)

(slide 20)

77
Q

When blood solubility of a gas is high, what are the effects?

A

Large amounts must be dissolved: PA/Pa is slow; induction prolonged
(so the gas want to stay in the blood and not diffuse into the brain= goes to sleep slower!)

(slide 20)

78
Q

Do we want our drug gases to have low or high solubility?

A

LOW!
Want these drugs to move down its concentration gradient out of the blood into the brain to go to sleep faster

(slide 20)

79
Q

Why would we choose a drug that takes a long time to go to sleep? Or that has a high solubility?

A

Cost!
That drug is probably cheaper and we get no say in matter! :(

(slide 20)
#Capitalism

80
Q

How is solubility temperature dependant?

A

If the temperature of the liquid (blood) increases, solubility decreases (the gas does not want to say in the blood, it wants to leave)

(slide 20)

81
Q
A

Anesthesia Pharm (Spring '24) - B (20 decks)

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