Clinical Question

[VCUBen]

I am not allowed to post on the official Clinical question board for good reason but I have a question regarding the MAC(minimal alveolar conc.) of gases. I don't need a lengthy response just a jumping off point. I recently shadowed a great CRNA in my area and he was trying to explain the origin of calculating the MAC of Sevo for example. I understand that it is 2 ( i believe) and that it means that half the population will experience amnesia at the concentration in the blood. (If I am wrong correct me ,please) My question is how is this number found and I understand that this only represents the level when no other agents are given but how does one figure out this concentration? Also how do you determine what concentration is appropriate along with other agents for example.

I would really like to read about it from a source since i am sure it is pretty complicated to explain. If someone want to post an answer on here then thanks in advance but I would equally appreciate being directed to a place to read about it for myself.

Thank you, sorry for not being in the right place. Thanks in advance!

[gasaholic]

have you tried google yet?

[FORANE]

I am not allowed to post on the official Clinical question board for good reason but I have a question regarding the MAC(minimal alveolar conc.) of gases. I don't need a lengthy response just a jumping off point. I recently shadowed a great CRNA in my area and he was trying to explain the origin of calculating the MAC of Sevo for example. I understand that it is 2 ( i believe) and that it means that half the population will experience amnesia at the concentration in the blood. (If I am wrong correct me ,please) My question is how is this number found and I understand that this only represents the level when no other agents are given but how does one figure out this concentration? Also how do you determine what concentration is appropriate along with other agents for example.

I would really like to read about it from a source since i am sure it is pretty complicated to explain. If someone want to post an answer on here then thanks in advance but I would equally appreciate being directed to a place to read about it for myself.

Thank you, sorry for not being in the right place. Thanks in advance!

MAC is actually the minimum alveolar concentration to prevent skeletal muscle movement in 50% of patients during surgical stimulation. The percent present in the alveoli presumably correlates with the percent in the brain when at steady state.
There is no exact "recipe" if you will allow me to use that term. Much of determining how much to give and what to give is experience based and patient response based.

[ethernaut]

MAC is actually the minimum alveolar concentration to prevent skeletal muscle movement in 50% of patients during surgical stimulation. The percent present in the alveoli presumably correlates with the percent in the brain when at steady state.
There is no exact "recipe" if you will allow me to use that term. Much of determining how much to give and what to give is experience based and patient response based.
i think we can go a little bit further and add to the definition by saying ... to prevent "purposeful" skeletal muscle movement...

[VCUBen]

Thanks for the responses. Is it true that the MAC is determined via research via clinical trial?

[ethernaut]

Thanks for the responses. Is it true that the MAC is determined via research via clinical trial?
??
don't you think any results occur because of such? c'mon... :cool2: maybe read some edmond eger (http://books.google.com/books?hl=en&num=100&resnum=0&q=edmond%20eger&um=1&ie=UTF-8&sa=N&tab=wp) or something..

[Anthony]

http://www.nurse-anesthesia.org/showthread.php?t=2864

Here - more than you'll really want to know
....and please do try to do your own good background reading....

[rbcsaver]

i think we can go a little bit further and add to the definition by saying ... to prevent "purposeful" skeletal muscle movement...

Incorrect! The 50% that move with MAC, is reflexive to surgical stimuli.
It is not "purposeful." MAC is of course a variable with consideration to age, +- N2O, narcotics,and more.
regards,
rbcsaver

[ethernaut]

Incorrect! The 50% that move with MAC, is reflexive to surgical stimuli.
It is not "purposeful." MAC is of course a variable with consideration to age, +- N2O, narcotics,and more.
regards,
rbcsaver
well, thanks for your first post. can you cite reference? also, while you're at it, why don't you define eger's supermaximal/submaximal stimuli/response.

[VCUBen]

"please do try to do your own good background reading"
I would love to do this, this is actually what I have been looking for , where do I start to get background information?


"more than you'll really want to know"
though it might seem odd but i really do want to know.

Where do you go to "look stuff up" besides your volumes of books? I attend VCU school of nursing so I have access to their subscribed databases fyi.

And thanks for putting in your input

[Anthony]

"please do try to do your own good background reading"
I would love to do this, this is actually what I have been looking for , where do I start to get background information?


"more than you'll really want to know"
though it might seem odd but i really do want to know.

Where do you go to "look stuff up" besides your volumes of books? I attend VCU school of nursing so I have access to their subscribed databases fyi.

And thanks for putting in your input

You start with the basic foundational readings found in most anesthesia specific textbook(s) - Google searches will just not due - once you have a firm understanding - you can then pursue specific avenues of related subtopics (ie PubMED)

If you then dont understand - go and speak to any provider - they should be able to give perspective and further direction. (In fact - you can do this at any step of the process)

regards

t

[VCUBen]

Thank you sir! My resident CRNA ( the one who I shadow with the most) offered to lend me a few textbooks so I guess i can start there.

[SuperSleeper]

:popcorn:

[SoonerFan]

I am not allowed to post on the official Clinical question board for good reason but I have a question regarding the MAC(minimal alveolar conc.) of gases. I don't need a lengthy response just a jumping off point. I recently shadowed a great CRNA in my area and he was trying to explain the origin of calculating the MAC of Sevo for example. I understand that it is 2 ( i believe) and that it means that half the population will experience amnesia at the concentration in the blood. (If I am wrong correct me ,please) My question is how is this number found and I understand that this only represents the level when no other agents are given but how does one figure out this concentration? Also how do you determine what concentration is appropriate along with other agents for example.

I would really like to read about it from a source since i am sure it is pretty complicated to explain. If someone want to post an answer on here then thanks in advance but I would equally appreciate being directed to a place to read about it for myself.

Thank you, sorry for not being in the right place. Thanks in advance!

MAC of any of the volatiles is based on research of healthy individuals ... what level of end-tidal Sevo (or whatever gas) keeps 50% of them from moving when the surgeon stimulates them. In theory, recall can occur @ a much lower level. If they take any meds, all bets may be off.

When you add any other drugs to your anesthetic regimen, such as narcs, that changes things, also. And if you use muscle relaxants, then movement isn't what you look @ to determine adequate level of anesthesia. There is absolutely no perfect formula that works for every patient.

Asking "how do you determine what concentration is appropriate along w/other agents?" is kind of like asking "how much sugar does subject A want in his tea?" It's different for every single subject. Some subjects "want" their tea really sweet, some "want" it just barely sweet. Some are used to (tolerant, for various reasons) 4tsp of sugar in their 16oz of tea, some can barely handle 1/2 tsp (no tolerance).

This is way over-simplified but hopefully I made a point, which is, only when you have experience anesthetizing many, many patients can you make an educated guess that will work well for the majority of your patients, & then not always. MAC levels are just a good starting-off point (or jumping-off point) that you adjust for every single patient based on age, health history, routine meds, type of surgery planned, etc.

[VCUBen]

MAC of any of the volatiles is based on research of healthy individuals ... what level of end-tidal Sevo (or whatever gas) keeps 50% of them from moving when the surgeon stimulates them. In theory, recall can occur @ a much lower level. If they take any meds, all bets may be off.

When you add any other drugs to your anesthetic regimen, such as narcs, that changes things, also. And if you use muscle relaxants, then movement isn't what you look @ to determine adequate level of anesthesia. There is absolutely no perfect formula that works for every patient.

Asking "how do you determine what concentration is appropriate along w/other agents?" is kind of like asking "how much sugar does subject A want in his tea?" It's different for every single subject. Some subjects "want" their tea really sweet, some "want" it just barely sweet. Some are used to (tolerant, for various reasons) 4tsp of sugar in their 16oz of tea, some can barely handle 1/2 tsp (no tolerance).

This is way over-simplified but hopefully I made a point, which is, only when you have experience anesthetizing many, many patients can you make an educated guess that will work well for the majority of your patients, & then not always. MAC levels are just a good starting-off point (or jumping-off point) that you adjust for every single patient based on age, health history, routine meds, type of surgery planned, etc.


I really appreciate this post, it makes perfect sense with the limited background knowledge I have right now. Thanks for you time to answer!:adore: :adore:

[gasaholic]

just curious, since you are in nursing school, why do you care about such specific subject matter?

[militarymd]

i think we can go a little bit further and add to the definition by saying ... to prevent "purposeful" skeletal muscle movement...

negative...

it is a measure of spinal cord reflex...

The des studies were done at ucsf......SINGLE agent anesthetic...meaning they had to MASK someone to sleep with des..no benzo...no narc...no lido...no nitrous......and the measure was movement...usually withdrawal...on skin incision.

[militarymd]

Thanks for the responses. Is it true that the MAC is determined via research via clinical trial?

yes...and they are difficult to do.

[stanman1968]

well, thanks for your first post. can you cite reference? also, while you're at it, why don't you define eger's supermaximal/submaximal stimuli/response.


here you are for MAC http://www.anesthesia-analgesia.org/cgi/content/full/93/4/947

[VCUBen]

just curious, since you are in nursing school, why do you care about such specific subject matter?

After shadowing a CRNA for a few times I just have developed an interest in how the mechanisms of anesthesia works. I know it might sound odd, I just have an interest. The more case studies I read, the more cases I watch the deeper my thirst for the "why and how" develops.

[ethernaut]

negative...

it is a measure of spinal cord reflex...

The des studies were done at ucsf......SINGLE agent anesthetic...meaning they had to MASK someone to sleep with des..no benzo...no narc...no lido...no nitrous......and the measure was movement...usually withdrawal...on skin incision.
i guess i'm an idiot then for listening to who ever told me that.

[SoonerFan]

negative...

it is a measure of spinal cord reflex...

The des studies were done at ucsf......SINGLE agent anesthetic...meaning they had to MASK someone to sleep with des..no benzo...no narc...no lido...no nitrous......and the measure was movement...usually withdrawal...on skin incision.

See, VCUBen? This is one of those many variables that affect MAC. Masking a patient is much less stimulating than sticking an ET tube down the throat, which sits there & is very irritating, or probably even moves around a tad w/the slightest repositioning of the patient, & irritates the trachea. So it will take less surgical stimulation w/an ET tube to cause movement than it will when the patient is masked. LMAs are kinda in between in degree of stimulation ... one of the many reasons we like 'em (less stimulating means less anesthetic gas needed w/all its potential side effects). Using an LTA w/an ETT, if it actually works, changes things, too. It's complicated.

[VCUBen]

I guess this is why Anesthesia is as much an art as a science. There is never only one way it has to be done.

Do many cases run with just gas these days?

[SoonerFan]

I guess this is why Anesthesia is as much an art as a science. There is never only one way it has to be done.

Do many cases run with just gas these days?

Some do, such as a BMT in a kid ... mask them to sleep w/Sevo, let the surgeon do his deal, then wake them up. Usually tho, they've had p.o. versed before, but not always. Also, some do T&As in kids w/nothing but gas, in which you mask them w/Sevo, someone starts an IV, then they get tubed w/o getting any IV drugs before or after, but they too may have gotten p.o. versed before.

There may be others. Just can't think of any right now.

[ethernaut]

Do many cases run with just gas these days?
yep. colonoscopies.

[SoonerFan]

yep. colonoscopies.

Does your group do colonoscopies using gas?

[RAYMAN]

Does your group do colonoscopies using gas?

Uhhh...I think that was a joke..colon...gas...get it?

[SoonerFan]

Uhhh...I think that was a joke..colon...gas...get it?

And I thought HE was dumb.

[ethernaut]

And I thought HE was dumb.
big ol' thumbs up here!! ;)

[B. F.]

A good book to start with is Basics of Anesthesia by Stolting and Miller. Some people refer to it as "Baby Miller" or Miller Light". It gives a lot of the basic foundations of anesthesia and is easy to read. Good Luck! BTW MAC can be used as a reference point from which to gague amounts of anesthetic. Like most anesthetics, volitle gases can be titrated to effect.

[Alrn1980]

VCU...if you really have an interest in anesthesia and are in nursing school - focus on your anatomy and physiology. Keep going over those concepts even after you are finished school and working as a nurse. It wouldn't hurt to buy "Basics of Anesthesia" by Stoelting, Miller (its like $50 on Amazon) - but only when you have an understanding of A&P.

With you are a nurse, try to focus on the science behind the therapies you are using. Like you said, look up and learn the "why" behind things. Even if you do not pursue any further formal degree or education, you will provide better care and earn respect of your coworkers and peers. If you decide to become an SRNA, then you will at least have the appreciation for the science behind the art and will have no problem putting the time and effort in to learn anesthesia.

[TranMan]

i guess i'm an idiot then for listening to who ever told me that.

Hey Ether. Just curious. Who told you that? or where did you read that?

thx

[ethernaut]

Hey Ether. Just curious. Who told you that? or where did you read that?

thx
an MD at one of my clinical sites way back when

[VCUBen]

VCU...if you really have an interest in anesthesia and are in nursing school - focus on your anatomy and physiology. Keep going over those concepts even after you are finished school and working as a nurse. It wouldn't hurt to buy "Basics of Anesthesia" by Stoelting, Miller (its like $50 on Amazon) - but only when you have an understanding of A&P.

With you are a nurse, try to focus on the science behind the therapies you are using. Like you said, look up and learn the "why" behind things. Even if you do not pursue any further formal degree or education, you will provide better care and earn respect of your coworkers and peers. If you decide to become an SRNA, then you will at least have the appreciation for the science behind the art and will have no problem putting the time and effort in to learn anesthesia.

Which materials would be the best in your opinion to brush up on this stuff? I was thinking of taking a grad phis class next fall as well.

[kirbybunny]

Which materials would be the best in your opinion to brush up on this stuff? I was thinking of taking a grad phis class next fall as well.

Advanced Mammalian Phys? Oh, I am having flashbacks! Good luck.

[SoonerFan]

Which materials would be the best in your opinion to brush up on this stuff? I was thinking of taking a grad phis class next fall as well.

Pharmacology.

No such thing as too much anatomy &/or physiology either.

[VCUBen]

Advanced Mammalian Phys? Oh, I am having flashbacks! Good luck.

Yeah, 5 days a week lol I look forward to that! My neighbor took it and he says it is interesting to say the least.