Concentration Effect

[suckstobeme]

Hey Guys-
I was wondering if you could help me out. What is the "concentration effect"? I started reading this basic anesthesia book and it tried to explain it, but I still didnt get it. Anybody out there have a good way of explaining it?

Thanks.

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[A4M]

You may need to find another book to read.

Basicly, say you have a mixture of 30% O2 and 70% N2O, in the lungs the N2O gets rapidly untaken, let's say 50%. Now you end up with a mixture of 46% O2 (30/(30+35)) and 54%N2O in the remainder of the lung volume. The empty 35% of your lung volume where the N2O use to be now takes in your original mixture of 30/70. Do a little math now you have a 40.5% O2 and 59.5% N2O. Whoa la, your O2 is more concentrated than your original mix. Thus "concentration effect".

This may not be the reality though, there are multiple papers in the late 90s to argue againt this view. Although the above explaination seems to serve me well to understand what the book is taking about.

 

[sevoflurane]

This is what I understand by concentration effect:

Let's say 50% of an anesthetic is taken up by the pulmonary circulation:

An inspired concentration of 10% (10 per 100 for simplicity) would result in an alveolar concentration 5/95=5.2% (the 5 is 50% of the inhaled anesthetic that is left in the lung after 50% of it has been absorbed by the pulmonary circulation.

Now, let's say that instead of an inspired concentration of 10% you jack up your anesthetic three times that to 50%. Again, 50% gets taken up by the pulmonary circulation which leaves you with an alveolar concentration of 25/75=33.3%

You essentially increased your original inspired concentration 5 fold from 10% to 50%. You would think that at a higher concentration your alveolar concentration should also go up 5 fold to 26% (5.2%x5) but in fact, your alveolar concentration actually went up from 5.2% to 33.3%.

In other words, even though 50% of anesthetic is taken up in both examples, a higher inspired concentration (10 to 50% in this case) results in a higher than expected (if you just multibply 5.2 x 5) increase in alveolar concentration of an anesthetic.

 

[sevoflurane]

You may need to find another book to read.

Basicly, say you have a mixture of 30% O2 and 70% N2O, in the lungs the N2O gets rapidly untaken, let's say 50%. Now you end up with a mixture of 46% O2 (30/(30+35)) and 54%N2O in the remainder of the lung volume. The empty 35% of your lung volume where the N2O use to be now takes in your original mixture of 30/70. Do a little math now you have a 40.5% O2 and 59.5% N2O. Whoa la, your O2 is more concentrated than your original mix. Thus "concentration effect".

This may not be the reality though, there are multiple papers in the late 90s to argue againt this view. Although the above explaination seems to serve me well to understand what the book is taking about.

I may be wrong here, but this sounds like second gas effect... I'm not really sure though cuz I think that second gas effect is an application of concentration effect. Hmmmm??? I better know this by my first intraining or I'll shoot myself. 😱

 

[MTGas2B]

I may be wrong here, but this sounds like second gas effect... I'm not really sure though cuz I think that second gas effect is an application of concentration effect.

I think of both, concentration effect and second gas effect as denominator effects. When you do you math the increased concentration comes from decreasing denominators.

 

[Platysma]

A4m's description of the concentration effect sounds more like a description of the second gas effect, while sevo's description of the concentration effect sounds basically correct to me.

With the concentration effect, what happens is that the higher the percentage of gas, the less effect pulmonary uptake has on decreasing the alveolar percentage. Pulmonary uptake is one of the reasons why Fa (the important number), doesn't instantly equal Fi. At the extreme case of the concentration effect, if you breathed 100% agent, even if 50% of the agent gets absorbed the inhaled percentage of the agent is the same (ie your lungs still contain nothing but agent), and Fa=Fi= 100%. At low Fa, the percentage drop of Fa is much more pronounced.

The concentration effect occurs regardless of the solubility of the gases apart from your agent. To figure out the magnitude of your concentration effect, you only look at the concentration of the agent you're interested in. The second gas effect, however, depends on the solubility of the gases OTHER than the agent you're interested in.

Imagine the extreme case where your agent is mixed with some magic gas with 100% absorption. Set your agent to 5% inhaled. In the lung, the 95% magic gas gets completely absorbed and you end up with 100% inhaled agent in the lung. Regardless of the initial concentration of yoru agent, the super-solubility of the magic gas, plus the second gas effect, enriches your agent to 100%.

So, the concentration effect and the second gas effect are not the same. I find that with these kinds of things it helps to understand them by imagining the extreme case.


Platysma
CA-1 NYPH-Columbia

I may be wrong here, but this sounds like second gas effect... I'm not really sure though cuz I think that second gas effect is an application of concentration effect. Hmmmm??? I better know this by my first intraining or I'll shoot myself. 😱

 

[Noyac]

Notice how none of the older guys here are commenting on this topic? That's b/c (at least in my case) we know what you are talking about but don't remember the particulars well enough to burn up the keyboard.

 

[jetproppilot]

Notice how none of the older guys here are commenting on this topic? That's b/c (at least in my case) we know what you are talking about but don't remember the particulars well enough to burn up the keyboard.

uhhhhhhhhhhhhhhh,..............soooooooo............................hmmmmmmmmmmmmm..............

anybody wanna dippa Copenhagen?

yeah my intimate knowledge of the concentration effect escapes me at the moment.... 😴

 

[Cali5921]

Yeah, this isn't real exciting stuff but this seems to be a well-liked test topic. Particularly because it is somewhat difficult to understand and easy to get confused with the second gas effect. Could anyone give an example of how a question might be posed regarding the concentration effect on the in- training exam?
Thanks

 

[SouthernGas]

I'm amused that the anesthesia texts consider this a "phenomenon" or "effect" when in fact it is really just simple consequence of a dilution problem.

Say I gave you a glass of iced tea and you let the ice melt. Then you drink half of the glass but instead of refilling if you poured in more tea. Well, guess what? The tea would be more concentrated. Maybe someone could publish that "phenomenon"?

 

[jetproppilot]

I'm amused that the anesthesia texts consider this a "phenomenon" or "effect" when in fact it is really just simple consequence of a dilution problem.

Say I gave you a glass of iced tea and you let the ice melt. Then you drink half of the glass but instead of refilling if you poured in more tea. Well, guess what? The tea would be more concentrated. Maybe someone could publish that "phenomenon"?

Does the Copenhagen Backwash when I take a swig of the diluted tea with a dip in affect the "effect"?

HAHAHAHHAHAHAHAHHAHAHAHAHAHAHHAHAHAHAHAHAHHAHAA

 

[BIS]

That was pretty funny