Lecture 11 (Exam 3) Inhaled Anesthetics Flashcards
What gas does a blue gas tank contain?
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)
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.
True!
3rd column:
Blue = Desflorane
Yellow = Sevoflorane
Purple = Isoflorane
(Dr Kane)
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)
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)
What is the “splitting ratio”?
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)
What controls the splitting valve/splitting ratio?
Control dial!
(Slide 44)
if the control dial is closed are you going to deliver any volatile gases to your patient?
No!
(Slide 44)
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?
They added wicks!
(Slide 44)
List the common inhaled anesthetics from fastest onset/offset to slowest onset/offset
Desflurane > Sevoflurane > Isoflurane
Slide 21
Which volatile anesthetic is the gold standard, but is no longer used?
Halothane
Slide 21
What is the blood:gas partition coefficient of Halothane?
2.54
Slide 22
What is the blood:gas partition coefficient of Enflurane?
1.90
Slide 22
What is the blood:gas partition coefficient of Isoflurane?
1.46
Slide 22
What is the blood:gas partition coefficient of Nitrous oxide?
0.46
Slide 22
What is the blood:gas partition coefficient of Desflurane?
0.42
Slide 22
What is the blood:gas partition coefficient of Sevoflurane?
0.69 *sexy sevo
Slide 22
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?
It wants to leave the blood - There will be a faster onset/offset
Slide 22
If the amount of volatile in the brain __________ patients wake up
Decreases
Slide 24
Timing of turning off your inhaled anesthetic is based on…
Its solubility
Slide 24
It takes the gas longer to be eliminated if the solubility is…
Higher
Slide 25
Name the following volatile anesthetic’s vapor pressures in units of torr:
- Desflurane (Suprane)
- Halothane:
- Isoflurane (Forane):
- Enflurane:
- Sevoflurane (Ultane):
Desflurane (Suprane): 669
Halothane: 243
Isoflurane (Forane): 238
Enflurane: 175
Sevoflurane (Ultane): 157
(“Dolphins Have Incredible Echolocation Skills” –> Dolphin made me think of water/vapor) 🐬
slide 42
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?
Dalton’s Law
Pgas1 + Pgas2 + Pgas3 … = Total pressure
Therefore, the total pressure of the 3 given partial pressures = 1.0 atm
(slide 38)
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?
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)
Define Vapor Pressure per the lecture slide.
Pressure at which vapor and liquid are at equilibrium
Where evaporation and condensation are equal
(slide 39)
“The amount of dissolved gas in a liquid is proportional to its partial pressure above the liquid” is known as…?
What does this law essentially describe for us as anesthetists?
What else does this mean?
Henry’s Law
“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)
____ increases vapor pressure
____ decreases vapor pressure
What does it mean if one particular gas has more vapor pressure?
Heat increases 🔥
Cold decreases 🧊
More volatile! Also means the gas is more likely to evaporate (think desflurane)
(slide 41)
Which of our volatiles has the highest and lowest vapor pressure?
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)
What decreases MAC requirements?
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
Mean BP <40mmHg (they are barely alive)
Cardiopulmonary bypass
Hyponatremia (without Na we are not depolarizing much per Dr. Kane)
Slide 32
What are the things that do not change MAC?
Chronic alcohol abuse
Gender ⚤
Duration of anesthesia
PaCO2 15-95 mmHg
PaO2 >38 mmHg
Blood pressure >40mmHg
Hyper/Hypokalemia
Thyroid gland dysfunction
Weight!
Slide 33
How does Volatile anesthetic (VA) work on spinal immobility?
⬇️ Depress excitatory AMPA and NMDA (glutamate receptors)
⬆ Enhance inhibitory glycine
Act on sodium channels.
(It does not cause paralysis, Its spinal mediated muscle relaxation. )
Slide 35
How does VA work on sodium channels?
VA interacts with subtypes of sodium channels which are expressed at the presynaptic junction, blocking the release of glutamate.
Slide 35
How does VA cause loss of consciousness in brain?
Augments inhibitory transmission of GABA in the brain, especially RAS
Potentiates glycine activation in brainstem.
No effect of volatiles on AMPA, NMDA or Kainate.
Slide 36
How do we administer Volatile Anesthetics?
Through Vaporizers.
(Refill vaporizers as you need)
Slide 37
Define Boyle’s Law.
At a constant temperature, pressure and volume of a gas are INVERSELY proportional.
Slide 4
Why do we care about Boyle’s law in anesthesia?
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.
Slide 4
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?
partial pressure gradient, solubility of the gas, thickness of the membrane
Fick’s Diffusion Law
Slide 5
What is one exception we learned in lecture (two substances we deal with a lot) to Graham’s Law? and why?
CO2 & O2 –> CO2 is more diffusible bc of its solubility!
Slide 6
The smaller the molecule, the ______ the effusion.
The process by which molecules diffuse through pores and channels without colliding describes which law?
smaller = faster the effusion
Graham’s Law of Effusion
I like to remember that graham crackers have holes (or pores)
Slide 6
With insoluble gases, recovery time is faster or slower?
Faster
Slide 26
Factors that alter MAC
Body Temp
Age (6% change per decade after 50 [decrease] and under 30 [increase])
MAC peaks at 1 years of age.
Slide 30
