Fresh Gas Flow

[OB1🤙]

What's your preference? Why?

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[BLADEMDA]

What's your preference? Why?

I use a lot of Sevoflurane and I prefer to run 2 liter flow just in case the surgery goes beyond 2 MAC hours. If I'm utilizing Iso for a long case my flows are 1.0 liter.

Since I cover at least 4 rooms I feel better knowing the CRNA is running 2 liters flow when utilizing Sevo. I'm aware of the literature showing that 1 liter is safe but the FDA still warns 2 liter flow for anything greater than 2 MAC hours.

 

[BLADEMDA]

Warnings
Although data from controlled clinical studies at low flow rates are limited, findings taken from patient and animal studies suggest that there is a potential for renal injury which is presumed due to Compound A. Animal and human studies demonstrate that Sevoflurane, USP administered for more than 2 MAC•hours and at fresh gas flow rates of <2 L/min may be associated with proteinuria and glycosuria.

While a level of Compound A exposure at which clinical nephrotoxicity might be expected to occur has not been established, it is prudent to consider all of the factors leading to Compound A exposure in humans, especially duration of exposure, fresh gas flow rate, and concentration of Sevoflurane, USP. During Sevoflurane, USP anesthesia the clinician should adjust inspired concentration and fresh gas flow rate to minimize exposure to Compound A. To minimize exposure to Compound A, Sevoflurane, USP exposure should not exceed 2 MAC•hours at flow rates of 1 to <2 L/min. Fresh gas flow rates <1 L/min are not recommended.

 

[OB1🤙]

Say that compound a was not a medicolegal concern. What flow would you use then?

 

[pgg]

Desflurane for just about everybody. Flows to 0.5 lpm right after induction, vaporizor set to 12. ET des rises gradually. By the time of incision, ET des is around 6-7. Used this way desflurane isn't any more expensive than sevo. We don't have isoflurane any more.

 

[OB1🤙]

Desflurane for just about everybody. Flows to 0.5 lpm right after induction, vaporizor set to 12. ET des rises gradually. By the time of incision, ET des is around 6-7. Used this way desflurane isn't any more expensive than sevo. We don't have isoflurane any more.

A man after my own heart! This is exactly what I do, though I admit to usually setting the dial to 1 L/m until I get ET of 6ish, then cut back to 0.4-0.5.

Des for almost all is my approach too. If running sevo, I bow to the lawyers and run it at 2 L/m as well.

I suspect our reasons are similar, but why do you do it this way?

Related question (to everyone): in your facility, how much does a bottle of des cost vs. a bottle of sevo?

 

[deleted59964]

sevo - about 1l, don't document fgf

 

[pgg]

A man after my own heart! This is exactly what I do, though I admit to usually setting the dial to 1 L/m until I get ET of 6ish, then cut back to 0.4-0.5.

Des for almost all is my approach too. If running sevo, I bow to the lawyers and run it at 2 L/m as well.

I suspect our reasons are similar, but why do you do it this way?

Related question (to everyone): in your facility, how much does a bottle of des cost vs. a bottle of sevo?

I prefer des over sevo not because of the faster wakeups in the OR (of course you can wake up anybody anytime on any gas with some practice) but because after wakeup, des keeps coming off faster, and they're more awake sooner in the PACU. That may or may not really speed PACU discharge, but I think it does (here, anyway).

0.5 lpm after induction is my goal, but if the OR crew is unusually efficient or it's a case that has quick prep time, I usually need to get it up closer to 1 lpm for a few minutes, otherwise ET might not be as high as I want it for incision.

 

[Noyac]

That how I use DES as well. I rarely use anything else.
The main reason I use DES tho is because it seems to be more analgesic at the start and throughout the case. I find I can use much less narcotics with DES. Also, you know how you are waiting for the case to start, like a knee scope, and your getting your ET up to MAC or so. You think you have a good amount of gas on board but when they make incision the pt jumps. This doesn't happen with DES.

 

[deleted171991]

When I had des, I used to run it at 0.5 L/min, after an initial higher flow to fill the circuit with 6-7% desflurane. Definitely my favorite inhaled anesthetic: fast wakeup, clear-minded patients. When I use 50% nitrous + sevo, I see something similar if I blow away the nitrous (go figure), while keeping patients on 0.4% sevo for the last 5-10 minutes of closing.

When using iso for long cases that were staying intubated, I used to run it at 0.5 L/min or lower until the very last minute (best anesthetic for transport).

With sevo (+/- nitrous), I use a FGF of 2L/min.

 

[kazuma]

I use both sevo and des and almost always at low flows, usually less than 0.5 L/Min. We use litholyme which reportedly does not produce compound A, CO, and it doesn't get very hot. I don't see a reason to not run low flows even for long cases with this type of absorbent especially when a bottle of sevo is $80-100 and des is $150 (our cost). Better conservation of heat and humidity plus less filling of the vaporizer. I can use the same bottle of des or sevo for a long time with low flows.

 

[dhb]

I find I can use much less narcotics with DES.

That's a bold statement! Never noticed this, i've shied away from des because of it's long degradation time.

 

[Spinach Dip]

That's a bold statement! Never noticed this, i've shied away from des because of it's long degradation time.

I think you mean 'elimination time.'



Also, why does no one use Iso? I thought it was the cheapest by far....?

 

[BLADEMDA]

I think you mean 'elimination time.'



Also, why does no one use Iso? I thought it was the cheapest by far....?

Any case over 2 hours (especially over 4 hours) I use Isoflurane with low FGF. The total cost of the vapor for a 6-8 hour case is probably about $2.

 

[dhb]

I think you mean 'elimination time.'

No
http://www.ncbi.nlm.nih.gov/pubmed/22492186

 

[sevoflurane]

.5 l/m or less.

It saves on gas $$$... but more importantly low flows:

1) Keeps your patients warm
2) Keeps your patients mucous membranes and AWs moist
3) Fast wake ups
4) It's part of the ninja anesthesia protocol

 

[sevoflurane]

BTW... you can run Sevo @ low flows. If I remember correctly, the study that specifically looked at compound A was done way back when on rats.
You can run it @ low flows for 2 MAC hours w/o concern. If you have CRF or insufficiency, just pick the better agent = DESFLURANE (as much as it pains me to say this ).

 

[pgg]

just pick the better agent = DESFLURANE (as much as it pains me to say this ).

Heh, that's funny. 🙂

I like the shifty looks some anesthesiologists get when they admit to using desflurane, like it's some kind of shameful thing, like staying home on a Friday night to eat a bucket of ice cream while watching a battered-woman movie on the Oxygen network with six cats.

When I was a resident, half my attendings scorned its use as a lazy wakeup crutch. I had one in particular who'd give me crap about using it, saying I was a better anesthesiologist than that 😱, how it's a a nurse gas that doesn't do anything well (whatever that means), that it's expensive and a waste of money, that Real Men only use halothane isoflurane sevoflurane. But I like it.

 

[pgg]

http://www.ncbi.nlm.nih.gov/pubmed/22492186

Desflurane and nitrous oxide should be restricted to cases where they may reduce morbidity and mortality over alternative drugs

because climate change?!?

I'd sooner quit eating steak because of cow farts.

 

[itwasalladream]

It saves on gas $$$... but more importantly low flows:

3) Fast wake ups

How does it lead to faster wakeups?

 

[pgg]

How [do low flows] lead to faster wakeups?

We had this conversation once before and I was not convinced, or maybe I just misunderstood the argument. The concept remains incongruent with my understanding of physics. Maybe he means something different by fast wake ups from low flows, or can explain it better.

http://forums.studentdoctor.net/threads/tips-for-fast-turnover-start-of-cases.858558/

DreamLover made the comment that low flows sped emergence on page 1, and the argument took off on page 2. Then there was an infusion of attitude into the thread 🙂 and then we got on to talking about the beauty of desflurane by page 3.

Here too:

http://forums.studentdoctor.net/threads/changing-agent-during-case.891693/

 

[sevoflurane]

PGG. You need to review your physics brah!

Did you consider a flex capacitor in your inhaled anesthetic calculations? How many gigawats we're you using in your reverse transformer. I hope it was 1.21 gigawatts, otherwise the whole thing will be off by 2 standard deviations.

 

[sevoflurane]

 

[pgg]

PGG. You need to review your physics brah!

We did that thread too, starting at post #40.

http://forums.studentdoctor.net/threads/the-battle-lines-are-drawn-romney-vs-obama.903749/

😀

 

[sevoflurane]

We did that thread too, starting at post #40.

http://forums.studentdoctor.net/threads/the-battle-lines-are-drawn-romney-vs-obama.903749/

😀

Smarteee-pants. 🙄

Somehow I missed that thread. Very nice. When space theory stuff comes on TV... I'm glued to it. Love it.
The Venus probe missions I find pretty amazing.

But yeah.... 1.21 gigawatts and a flex capacitor. 😉

 

[deansrv72]

From what I've heard (and read little about), Des is second only to Nitrous in terms of hanging around the atmosphere...from the volatiles that anesthesia providers use regularly. I don't have data at hand to support my statements though.

And regarding low FGF, shouldn't there be a concern about having FGFs that are lower (in volume) than dead space plus patient's Vt? Unless one is using a closed circuit system, seems more rebreathing (of CO2) would occur than wanted/necessary. With a spontaneously ventilating patient, might as well institute a 'closed circuit' system.

 

[BuzzPhreed]

[pedantic]

I believe it's a "flux" capacitor.

[/pedantic]

 

[OB1🤙]

Great Scott, it's flux capacitor!

Thanks for the discussion. You guys hit on the major points I was hoping to make. Mostly, that low flow des doesn't cost any/much more than sevo at 2 L/m, and the faster wakeups and PACU discharges may make that money back.

Noy- that's an interesting take regarding analgesia. I hadn't noticed that but just another reason to like des.

I have some partners who have made the greenhouse gas point and for awhile, I cut back on my des use because, you know, the environment. But then I realized that the delicious ribeye I went home and grilled probably caused more greenhouse gas in its production than my 0.4L/m of desflurane for that day's case, and decided it that unless I was willing to go vegan, I could continue to use desflurane without worrying about my role in warming the earth.

Someone showed me this talk once and I'll post it for the benefit of the residents and anyone else who is interested- a good take on the benefits of reducing flows. Worth the time it takes to go through these slides. http://etherweb.bwh.harvard.edu/education/PHILIP/Tech_Block_04/1_LowFlowO2Agt.pdf

 

[itwasalladream]

Thanks. I'm not convinced either. But maybe I'm missing something.

 

[dhb]

I do sevo @ 0.4L/min btw

 

[Ipassgas]

And I thought I was saving money running it at 0.7 LPM, half air, half O2. I guess I need to up my ninja game.

 

[Noyac]

I do sevo @ 0.4L/min btw

That's nearly a close circuit depending on the size of the pt.

 

[periopdoc]

Des at 0.3-0.5 maintaining 50%-80% fiO2 for all the reasons listed above. Flow is mostly dependent on which anesthesia machine I am stuck with for the day. You only need to provide enough oxygen to keep up with consumption and enough FGF to keep up with leaks and sampling volume. You can feed the sampling exhaust back into the system to get even lower flows.

I agree that DES is significantly more analgesic.

- pod

 

[OB1🤙]

Corollary to all the above: I much prefer a vent with a bellows rather than one with a piston. I like being able to see that bellows rise, and knowing whether I have to search for a leak in the circuit.