How is MAC measured

[OrbitalOverload]

Can someone smarter than me please explain how it is ethical to measure Mean Alveolar Concentration for a given inhaled anesthetic?

MAC is defined as the concentration of gaseous anesthetic (as a percentage of 1ATM of gas in the alveoli) that will result in immobility in 50% of patients when exposed to a noxious stimulus such as a surgical incision.

I don't understand how this value could be determined without an unethical experiment in which patients are subjected to low concentrations of anesthesia and observed to see if they jolt when a surgeon incises them.

Thank you in advance!

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[deleted171991]

Can someone smarter than me please explain how it is ethical to measure Mean Alveolar Concentration for a given inhaled anesthetic?

MAC is defined as the concentration of gaseous anesthetic (as a percentage of 1ATM of gas in the alveoli) that will result in immobility in 50% of patients when exposed to a noxious stimulus such as a surgical incision.

I don't understand how this value could be determined without an unethical experiment in which patients are subjected to low concentrations of anesthesia and observed to see if they jolt when a surgeon incises them.

Thank you in advance!

It was unethical, but done on animals, I'd guess.

 

[deleted162650]

Not unethical if done in willing volunteers who understood what they were getting themselves into and done back in the day before we all turned into pansies. My guess is that early investigators did the experiments on themselves. The early work on curare including dose finding experiments were done through self experimentation by some pioneering badass anesthesiologists.

 

[Psai]

Not unethical if done in willing volunteers who understood what they were getting themselves into and done back in the day before we all turned into pansies. My guess is that early investigators did the experiments on themselves. The early work on curare including dose finding experiments were done through self experimentation by some pioneering badass anesthesiologists.

My mind was blown when I read about how Werner Forssmann catheterized himself before it was a thing but no that wasn't enough, he even walked to an x-ray machine to push it in further fluoroscopically

 

[deleted162650]

How bout Bier doing a cocaine spinal on himself.

 

[OrbitalOverload]

Not unethical if done in willing volunteers who understood what they were getting themselves into and done back in the day before we all turned into pansies. My guess is that early investigators did the experiments on themselves. The early work on curare including dose finding experiments were done through self experimentation by some pioneering badass anesthesiologists.

This makes sense for earlier anesthetics like cocaine, ether etc. but probably doesn't apply to newer ones like sevoflurane that were developed after the medical world developed an ethical conscious.

 

[deleted162650]

You may be surprised. Most of the work on how anesthetics affect SSEP's, MEP's, etc. were done by the faculty where I trained on each other. It was great listening to those guy's stories about being on barbiturates, ketamine, preceded, opioids, etc.

 

[vector2]

 

[pgg]

How bout Bier doing a cocaine spinal on himself.

Too bad no one knew how to do a blood patch 48h later ...

 

[vector2]

Too bad no one knew how to do a blood patch 48h later ...

Headache, you say? He lived in the right place at the right time

 

[deleted162650]

Too bad no one knew how to do a blood patch 48h later ...

Yup. First 2 SAB's (Bier and then his assistant) were also the first 2 documented PDPH's. I'm impressed that Bier correctly postulated that PDPH was 2/2 to loss of CSF.

 

[Mman]

Yup. First 2 SAB's (Bier and then his assistant) were also the first 2 documented PDPH's. I'm impressed that Bier correctly postulated that PDPH was 2/2 to loss of CSF.

his initial assumption was that it was from the copious amounts of beer they consumed in celebration later that night

 

[Robotic Wis-Hipple]

Initial studies were done in dogs (edited, I thought it was rats initially), surgical stimuli was clamping of their tails under various alveolar gas levels:

Eger EI 2nd, Saidman LJ, Brandstater B. Minimum alveolar anesthetic concentration: a standard of anesthetic potency. Anesthesiology 1965; 26: 756–63.

Equipotent dosing between volatiles was confirmed in dogs as well:

Eger EI 2nd, Brandstater B, Saidman LJ, Regan MJ, Severing- haus JW, Munson ES. Equipotent alveolar concentrations of methoxyflurane, halothane, diethyl ether, fluroxene, cyclopro- pane, xenon and nitrous oxide in the dog. Anesthesiology 1965; 26: 771–7.


Subsequent studies were done on volunteers:

Quasha AL, Eger EI 2nd, Tinker JH. Determination and applica- tions of MAC. Anesthesiology 1980; 53: 315–34.

 

[vector2]

Initial studies were done in rats, surgical stimuli was clamping of their tails under various alveolar gas levels:

Eger EI

Eger EI

Eger EI

Can't believe I've never heard of this guy. He has 588 publications ranging from 1958 to 2015.

http://profiles.ucsf.edu/edmond.eger

 

[pgg]

his initial assumption was that it was from the copious amounts of beer they consumed in celebration later that night

Love it. Presumably the "hangover" didn't go away with breakfast and he moved on to hypothesis #2.

 

[Robotic Wis-Hipple]

Can't believe I've never heard of this guy. He has 588 publications ranging from 1958 to 2015.

http://profiles.ucsf.edu/edmond.eger

Yeah, he did some of if not the first studies on rate of rise of PaCO2 during apnea under GA that people talk about all the time too.

 

[vector2]

 

[Psai]

Can't believe I've never heard of this guy. He has 588 publications ranging from 1958 to 2015.

http://profiles.ucsf.edu/edmond.eger

Yeah pretty much every paper I read when I was in lab was either co-authored by him or depended heavily on one of the principles he derived

 

[deleted162650]

Can't believe I've never heard of this guy. He has 588 publications ranging from 1958 to 2015.

http://profiles.ucsf.edu/edmond.eger

Yes, Eger was certainly one of the pioneers and contributed a ton to this field. It's a shame that later in his career he basically sold his soul to Baxter and a became a total industry ***** for Desflurane.

Saidman and Benumof are other guys to get familiar with if you like the pulm phys aspects of Anesthesia.

 

[OrbitalOverload]

Thank you for this great info!

 

[Urzuz]

Can't believe I've never heard of this guy. He has 588 publications ranging from 1958 to 2015.

http://profiles.ucsf.edu/edmond.eger

He's the one who originally coined the term MAC (which -- can't believe no one pointed this out to the OP -- stands for MINIMUM alveolar concentration, not mean).

Even more amazing is that he is still sharp as a tac and shows up to work. I feel extraordinarily privileged that he even gave us our lectures on MAC and inhalational anesthetics!

 

[partydoc]

He's the one who originally coined the term MAC (which -- can't believe no one pointed this out to the OP -- stands for MINIMUM alveolar concentration, not mean).

Even more amazing is that he is still sharp as a tac and shows up to work. I feel extraordinarily privileged that he even gave us our lectures on MAC and inhalational anesthetics!

That's awesome, he's definitely one of the giants in the field.

 

[Psai]

He's the one who originally coined the term MAC (which -- can't believe no one pointed this out to the OP -- stands for MINIMUM alveolar concentration, not mean).

Even more amazing is that he is still sharp as a tac and shows up to work. I feel extraordinarily privileged that he even gave us our lectures on MAC and inhalational anesthetics!

I can't believe he shows up to work either. When I hear Eger, I think of Meyer and Overton

 

[urge]

Some of my not so old attendings told me stories about practicing nerve blocks on each other back in the day before ultrasound or stimulator.

 

[soorg]

You're all full of it-it's common knowledge that nurses made all these discoveries in their neverending quest to take care of the whole patient while the over-trained doctors were busy playing golf.

 

[Urzuz]

You're all full of it-it's common knowledge that nurses made all these discoveries in their neverending quest to take care of the whole patient while the over-trained doctors were busy playing golf.

I obviously know your post is meant to be joking...but it honestly makes me f*cking sick to my stomach. Look at Dr. Eger's seemingly endless publication list on the faculty website provided: http://profiles.ucsf.edu/edmond.eger

And just think that there is a murse living in rural BFE who has the audacity to say that his online degree and couple months of following physicians' orders amidst his mandatory lunch breaks is equivalent (or even superior) to everything Dr. Eger has accomplished in his career. I can tell you that he truly loves the specialty and the work he did and continues to do, and probably wouldn't be phased at all by these murses claiming "equivalence", but it honestly makes me want to vomit thinking about this.

And to be clear, I know that I am a speck of dust in the shadow of these giants in our field. The difference is that I at least have the humility to admit as much.