ACE question about Fa/Fi and cardiac output

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TheRoc

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So I'm doing some practice questions to prepare to written boards next week (yikes!) and I must admit I'm stumped by this question. A decrease in cardiac output will have the LEAST impact on the rate of change to the FA/FI ratio for which volatile agent? Options are like sevo, iso, des, nitrous.

I would have picked nitrous oxide. Least soluble, least effect of cardiac output on FA/FI since very little is taken up anyway. The printed answer is isoflurane and the explanation says it's because it has the largest blood-gas partition coefficient, is the least soluble, and therefore would have least impact of FA/FI during states of decreased cardiac output. Huh? I really thought I understood this until now!

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This is the typical ivory tower-question real life-clinicians don't give a crap about. Knowing the answer has about the same impact on improving anesthetic care as knowing the exact value of Moon gravity. (1.622 m/s2, for the curious)
 
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This is the typical ivory tower-question real life-clinicians don't give a crap about. Knowing the answer has about the same impact on improving anesthetic care as knowing the exact value of Moon gravity. (1.622 m/s2, for the curious)

Regardless, this is the type of crap I need to know in order to pass the written boards so I can take the oral boards so I can be board-certified. Sigh. Any help from others?
 
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I know the question you are referring to. I spoke with a few of my fellow residents about it and we all think it was a misprint. Check out hall q 333 which contradicts it.
 
Does the answer really say isoflurane is the least soluble? What ACE exam is that?

2012 9A, question 42. Direct quote: "Compared to sevoflurane, desflurane, and nitrous oxide, isoflurane has the largest blood-gas partition coefficient, is the least soluble anesthetic gas, and would have the lowest impact on the rate of change to FA/FI during conditions that result in decreased cardiac output."
 
I would think the answer is desflurane. Decreasing CO would increase the rise in FA/FI, speeding induction. For an agent that already is fast because it is insoluble (des) it would have the least effect. I assume that I so would have the greatest effect by change of CO.

This sound right ?
 
I would think the answer is desflurane. Decreasing CO would increase the rise in FA/FI, speeding induction. For an agent that already is fast because it is insoluble (des) it would have the least effect. I assume that I so would have the greatest effect by change of CO.

This sound right ?

That is correct.
 
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Thank you for clarifying the answer . I was stumped !
How good is ACE.ASAHQ.ORG MCQs for written Boards preparation ?
 
This is the typical ivory tower-question real life-clinicians don't give a crap about. Knowing the answer has about the same impact on improving anesthetic care as knowing the exact value of Moon gravity. (1.622 m/s2, for the curious)

FFP, never missing a chance to go on a random unhelpful tirade
 
So I'm doing some practice questions to prepare to written boards next week (yikes!) and I must admit I'm stumped by this question. A decrease in cardiac output will have the LEAST impact on the rate of change to the FA/FI ratio for which volatile agent? Options are like sevo, iso, des, nitrous.

I would have picked nitrous oxide. Least soluble, least effect of cardiac output on FA/FI since very little is taken up anyway. The printed answer is isoflurane and the explanation says it's because it has the largest blood-gas partition coefficient, is the least soluble, and therefore would have least impact of FA/FI during states of decreased cardiac output. Huh? I really thought I understood this until now!

I thought the answer was iso, b/c its Fa/Fi is low no matter what the circumstances. Iso is the MOST soluble in blood of those choices btw.
 
Nevermind, I was wrong, here's the relevant figure
upload_2015-2-5_21-16-33.png
 
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Like others have said, it's probably des.

If we are wrong (I always forget the des-nitrous order for partition constants), it's nitrous.
 
Like others have said, it's probably des.

If we are wrong (I always forget the des-nitrous order for partition constants), it's nitrous.

On the FA/FI curve, it's nitrous, des, sevo, iso, halothane.

BG coefficients are .42 (des), .47 (nitrous), .65 (sevo), 1.4 (iso), 2.4 (halo).

Nitrous is on top of the FA/FI curve despite having a (slightly) higher BG partition coefficient than des because of the concentration effect. Nitrous gets a boost from the fact that we deliver it at much higher percentages than desflurane.
 
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