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Old 10-10-2012
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Question Halothane vs Methoxyflurane

Halothane has blood:gas coefficient and oil:gass partition coefficient of 2.4 and 220, respectively.
Methoxyflurane has b:g and o:g coefficient of 13 and 950.
Which is true?

1) both result in faster induction than does NO (b:g of .47)
2) MAC of halothane is less than that of methoxyflurane
3) Both useful b/c no cardiodepressant
4) Recovery from methoxyflurane is faster than that from halothane
5) An increase in ventilation rate makes the onset of anesthesia more rapid for either agent.
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Old 10-10-2012
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My ans is MAC of halothane is lesser than methoxyflurane
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Old 10-10-2012
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Quote:
Originally Posted by SOBE223 View Post
Halothane has blood:gas coefficient and oil:gass partition coefficient of 2.4 and 220, respectively.
Methoxyflurane has b:g and o:g coefficient of 13 and 950.
Which is true?

1) both result in faster induction than does NO (b:g of .47)
2) MAC of halothane is less than that of methoxyflurane
3) Both useful b/c no cardiodepressant
4) Recovery from methoxyflurane is faster than that from halothane
5) An increase in ventilation rate makes the onset of anesthesia more rapid for either agent.
After ruling out other options I left with
5) An increase in ventilation rate makes the onset of anesthesia more rapid for either agent.

As, solubility = potency= 1/MAC
Less soluble= rapid induction and recovery time
All thanes are cardiodepressent.


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Old 10-10-2012
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Will go with no. 2.
Oil:gas coefficient reverses to give lipid solubility?
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Old 10-10-2012
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Here is my silly little way;
Gas anathetic with high B:G ratio are more soluble in the blood/lipids, so the they are not readily available as "free" in the CNS to induce the anesthesia. As they are soluble, tissues would provide a prolonged supply for these gas to get into CNS, prolonging the anesthesia, i.e. the higher the B:G ratio, the slower the gas both in iduction and recovery. But for the gas to get into the CNS, it must first be "solublized" in the blood, and this is done by increasing its conc. in the alveoli ( MAC ). So, an agents with low B:G ratio would have higher MAC and so less potent ( because we have needed more dose to reach the same ED 50). Putting all these thought together:
B:G:
NO = 0.5
Halothane = 2.4
methoxyflurane = 13, then
Blood solubility ( and so rapidity ) : NO < halo. < methoxy., then
MAC ( and so potency ) : NO > halo. > Methoxy.
***
Halo and methoxy do not act faster than NO so A is incorrect.
MAC of halo. is not less than that of methoxy. so B is obviously incorrect.
The only inhaled anathetic that does not produce cardiodepression is NO so C is wrong.
Recovery from methoxy. is by far slower than that of halo. D is incorrect.
And we left with E, which I have strong feeling that its the right answer but I dont know exactly why!

Last edited by Awwad; 10-10-2012 at 12:49 PM.
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