Simplified explanation for why Des needs to be heated??

[jihong]

Hey everyone,

I'm trying to understand why desflurane needs to be heated. I've read that due to desflurane's boiling point being near room temperature, you want to prevent it from boiling and there's another reason having to do with its volatility near atm pressure and that how it has a high vapor pressure, but heating it seems counter intuitive, hence why I'm asking for an explanation.

Wouldn't heating it to 39 C and increasing the pressure to 1500 mmHg INCREASE the amount of agent that's in vapor form? Why would you want to increase the amount in vapor form? When you don't want the volatile agent to boil, why do you want to heat it up? By heating it, you're leaving more of the gas in vapor form, is this just to help control the delivery of the gas because it's attribute make it difficult to predict how much is in gas vs liquid form at room temp and atm pressure?

Thanks!

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[urge]

Hey everyone,

I'm trying to understand why desflurane needs to be heated. I've read that due to desflurane's boiling point being near room temperature, you want to prevent it from boiling and there's another reason having to do with its volatility near atm pressure and that how it has a high vapor pressure, but heating it seems counter intuitive, hence why I'm asking for an explanation.

Wouldn't heating it to 39 C and increasing the pressure to 1500 mmHg INCREASE the amount of agent that's in vapor form? Why would you want to increase the amount in vapor form? When you don't want the volatile agent to boil, why do you want to heat it up? By heating it, you're leaving more of the gas in vapor form, is this just to help control the delivery of the gas because it's attribute make it difficult to predict how much is in gas vs liquid form at room temp and atm pressure?

Thanks!

This, in bold.

There are ORs at 25 degrees, and ORs at below 20 degrees. It would be a nightmare to regulate it at room temp.

 

[cchoukal]

As I have always understood it, it has to do with the high vapor pressure and the fact that boiling point is so close to room temperature. Evaporation is endothermic, so as soon as vaporization begins, the apparatus cools and vaporization may cease. The Des "vaporizer" isn't so much a vaporizer in the way the others are. The others are variable-bypass, meaning your dial shunts more fresh gas flow through the sump where it picks up a predictable amount of vapor (because the boiling point is far from room temperature). Because vaporization varies with temperature in a sigmoidal fashion, small changes in the ambient temperature of the apparatus will lead to huge swings in the amount of vapor present. For Des, the delivery device heats the Des so it's all vapor and the dial, instead of adjusting fresh gas flow through the sump, instead adjusts a jet of Des vapor into the carrier gas. I suppose, alternative, Des vaporizers could be cooled, but that's much more complicated. The point is just to take it away from room temperature so that the small changes in temp associated with vaporization don't lead to wild swings in the fraction of vapor present.

 

[deleted171991]

Another piece of irrelevant engineering information anesthesiologists are burdened with.

 

[Planktonmd]

It needs to be warmed because it's a crappy inhaled agent!

 

[pgg]

It needs to be warmed because it's a crappy inhaled agent!

Oh no you di'int!