Sevo vaporizer

[Low Flow]

CA-1 at an academic hospital that has recently made the push to use 1 L/min fresh gas flows. When I started a few months ago the general practice was to not go <2 L/min.

This has me thinking... which scenario uses less liquid sevo: 2.5% at 2 L/min or 4% at 1 L/min? I’ve noticed during the first hour of a procedure you really have to jack up the %sevo to maintain 1 MAC.

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[DrOwnage]

The real world answer to your question is: probably trivial and doesn't matter unless you're using Des for every case. You're probably talking about a cost difference of a couple of dollars every day. I think anything from 1-2L of FGF for maintenance is reasonable.

This is a good pdf. It's where I got my rationale to keep my flows at 4L for about 10-15 minutes after intubation before turning them down low due to expired fractions and time constants.

http://www.csen.com/LFAD.pdf

 

[drmwvr]

.025 X 2000 = 50 ml .04 X 1000 = 40 ml.... don't even need to do the conversion to liquid agent if you don't want to.

 

[deleted875186]

Calculation of volatile anaesthetics consumption from agent concentration and fresh gas flow - PubMed

By application of the presented specific volatile agent constants and equations, it becomes easy to calculate volatile agent consumption if the fresh gas flows and the resulting inhaled concentration of the volatile agent are known. By this method, it is possible to extract data about volatile...

pubmed.ncbi.nlm.nih.gov

You can calculate how much liquid sevo you use per hour for each scenario. It’s true the lower your FGF, you have to dial up the percent sevo for maintenance. The cost savings are there though, not trivial, if your talking about every provider doing this for so many hours a day in the whole department. Iso is ridiculously cheap, doesn’t matter, it’s 10 dollars a bottle or something. Sevo is somewhere around 80 dollars a bottle.

I’m a firm believer of ultra low flows with sevo, except for very long cases, may not be safe for very long cases, so I use iso for the all day case. Nobody is expecting a wake up on a dime on an all day case anyway.

 

[MirrorTodd]

Calculation of volatile anaesthetics consumption from agent concentration and fresh gas flow - PubMed

By application of the presented specific volatile agent constants and equations, it becomes easy to calculate volatile agent consumption if the fresh gas flows and the resulting inhaled concentration of the volatile agent are known. By this method, it is possible to extract data about volatile...

pubmed.ncbi.nlm.nih.gov

You can calculate how much liquid sevo you use per hour for each scenario. It’s true the lower your FGF, you have to dial up the percent sevo for maintenance. The cost savings are there though, not trivial, if your talking about every provider doing this for so many hours a day in the whole department. Iso is ridiculously cheap, doesn’t matter, it’s 10 dollars a bottle or something. Sevo is somewhere around 80 dollars a bottle.

I’m a firm believer of ultra low flows with sevo, except for very long cases, may not be safe for very long cases, so I use iso for the all day case. Nobody is expecting a wake up on a dime on an all day case anyway.

Except for the neurosurgeons.

 

[Iso4ane]

Most of the GE machines (and Im pretty sure the Dragers will too) have a screen where you can see your fresh gas and volatile usage.

 

[Mman]

I’ve noticed during the first hour of a procedure you really have to jack up the %sevo to maintain 1 MAC.

The reason you need the dial up higher initially at low flows is because most of what the patient is inhaling is what they just exhaled. If you have a 5 L minute ventilation and FGF of 1L/min, then 80% of their inhaled breath is what they just exhaled (after being scrubbed of CO2). So if you are trying to get them deeper, it takes a lot higher number on the vaporizer because your flows are so low. It is the same reason you need to turn your flows up at the end of the case to wake them up because if you don't they will just rebreathe the same sevo molecules over and over.

 

[deleted59964]

there is an environmental cost ... use low flow.

 

[coffeebythelake]

CA-1 at an academic hospital that has recently made the push to use 1 L/min fresh gas flows. When I started a few months ago the general practice was to not go <2 L/min.

This has me thinking... which scenario uses less liquid sevo: 2.5% at 2 L/min or 4% at 1 L/min? I’ve noticed during the first hour of a procedure you really have to jack up the %sevo to maintain 1 MAC.

Not less than 2L/min was based on old thinking that sevo produced compound A and caused fluoride induced nephrotoxicity. based on animal studies. has not been shown to cause problems in humans. high FGF ultimately leads to high waste of sevo. I typically use ultra-low flow (<0.5 L/min) after intubation and during maintenance phase, and overpressurize the system if necessary to ensure enough sevo molecules go to the patient's brain.

 

[epidural man]

People still use volatiles?

 

[coffeebythelake]

People still use volatiles?

Eh.. What do u use? Rubber mallet?

 

[epidural man]

Eh.. What do u use? Rubber mallet?

acupuncture and hypnosis.

 

[dhb]

0.4L/min all day

 

[deleted59964]

Eh.. What do u use?

not sure if serious?

 

[Iso4ane]

Eh.. What do u use? Rubber mallet?

Rubber? Nah too high a risk of latex allergy. We use stainless steel.

 

[drmwvr]

Calculation of volatile anaesthetics consumption from agent concentration and fresh gas flow - PubMed

By application of the presented specific volatile agent constants and equations, it becomes easy to calculate volatile agent consumption if the fresh gas flows and the resulting inhaled concentration of the volatile agent are known. By this method, it is possible to extract data about volatile...

pubmed.ncbi.nlm.nih.gov

... so I use iso for the all day case. Nobody is expecting a wake up on a dime on an all day case anyway.

What I wouldn't do for an isoflurane vaporizer...you must work at Valhalla General....

 

[deleted59964]

acupuncture and hypnosis.

i’ve heard there is this fancy white medicine -

 

[zizzer]

.025 X 2000 = 50 ml .04 X 1000 = 40 ml.... don't even need to do the conversion to liquid agent if you don't want to.

This.

Also, make sure you're basing your inspired gases on what's actually being measured, not what's being set as the percentage of fresh gas flow since FGF is only part of what's being inspired.

Think of the FGF settings as the numbers that show up when you change the volume on your TV. They don't really correspond to measurements, but you adjust it up and down to get to the effect you want. Similarly, with low FGF, turn up the vaporizer percent until you get the measured inhaled and exhaled agent percentage you want.

 

[propadope]

One thing to consider is that sodalyme and baralyme produce Compound A and CO. The newer generation absorbers like Amsorb plus or Sodasorb LF do not and are designed for low flow. Not sure about cost comparison between the two

 

[btbam]

This.

Also, make sure you're basing your inspired gases on what's actually being measured, not what's being set as the percentage of fresh gas flow since FGF is only part of what's being inspired.

Think of the FGF settings as the numbers that show up when you change the volume on your TV. They don't really correspond to measurements, but you adjust it up and down to get to the effect you want. Similarly, with low FGF, turn up the vaporizer percent until you get the measured inhaled and exhaled agent percentage you want.

Why do you care what the inspired agent percentage is? The exhaled is what the brain is seeing, only relevant number imo.

 

[deleted162650]

What I wouldn't do for an isoflurane vaporizer...you must work at Valhalla General....

I’ll do you one better

 

[abolt18]

What I wouldn't do for an isoflurane vaporizer...you must work at Valhalla General....

You actually don't have iso???

 

[Drwine]

You actually don't have iso???

We got rid of it 20 years ago and I don't miss that I haven't used it in 20 years. IMHO iso was the anesthesia equivalent of the 16 bit computer chip and compact fluorescent light bulb. Generic sevo made it obsolete in first world countries.

 

[GassYous]

We got rid of it 20 years ago and I don't miss that I haven't used it in 20 years. IMHO iso was the anesthesia equivalent of the 16 bit computer chip and compact fluorescent light bulb. Generic sevo made it obsolete in first world countries.

I use iso everrday. Cheap, nice to use with some prop, comes off predictably when used at lower macs.

 

[coffeebythelake]

I use iso everrday. Cheap, nice to use with some prop, comes off predictably when used at lower macs.

Also great for long cases where u plan to keep patient tubed for the ICU

 

[coffeebythelake]

We got rid of it 20 years ago and I don't miss that I haven't used it in 20 years. IMHO iso was the anesthesia equivalent of the 16 bit computer chip and compact fluorescent light bulb. Generic sevo made it obsolete in first world countries.

How long have you been practicing. You know there were other halogenated volatile anesthetics before iso.. u talk as if you've never heard of halothane

 

[Norepi]

Seitsonen ER, Yli-Hankala AM, Korttila KT. Similar recovery from bispectral index-titrated isoflurane and sevoflurane anesthesia after outpatient gynecological surgery. J Clin Anesth. 2006;18(4):272-279. doi:10.1016/j.jclinane.2005.12.005

Zuckerman R, Sakima N, Parker SD, Fleisher LA. Comparison of recovery profile after ambulatory anesthesia with propofol, isoflurane, sevoflurane and desflurane: a systematic review. Anesth Analg. 2004;98(3):. doi:10.1213/01.ane.0000103187.70627.57

Maheshwari K, Ahuja S, Mascha EJ, et al. Effect of Sevoflurane Versus Isoflurane on Emergence Time and Postanesthesia Care Unit Length of Stay: An Alternating Intervention Trial. Anesth Analg. 2020;130(2):360-366.

Long story short - there is little difference in recovery time between sevo and iso regardless of case duration. There are other variables we are neglecting when thinking about emergence time aside from the blood gas partition coefficient - namely things like the blood muscle and fat coefficients which are significant contributors to central compartment redistribution and emergence. Turns out these variables are very similar between the two gases. In these studies the difference in time to extubation was like 7 minutes or something in the worst case scenario where the gas is turned from 100 to 0 while the dressings are going on (worst case scenario.)

In addition, I understand that newer calcium based CO2 absorbant species do not appreciably at all generate compound A formation - however there's just something that gives me the heeby-jeebys about not obeying the sevoflurane FDA label's own recommendation to not run more than <2L FGF for 2MAC hour or greater cases etc.

That all being said, I feel much better about running Iso and low flows (<1L FGF) because it is better for the environment and patient (temp and humidity savings blah blah), but also I believe the cost between consumed gas and consumed absorbant sweet spot is 1L for isoflurane (and might be the same for sevo, but see above).

 

[drmwvr]

You actually don't have iso???

Nope...when the newer machine yokes would only accept 2 vaporizers, des and sevo were given those spots...over time it was just a hassle to move vaporizers on and off so folks just stopped. Eventually, with storage space being at a premium iso just disappeared along with halothane and ethrane. I think there may be some liquid agent and a vaporizer or two somewhere in the whole system somewhere, but getting it would be a hassle.

Best agent I know of for combined epidural/GA...very potent at lower MAC and patients wake up as crisp as a potato chip.....

 

[Twiggidy]

I pretty much only do TIVA or Iso, but I also don't spend too much time in ASCs or do high pressured outpatient procedures so they can take all the time they need to wake up in PACU in my book

 

[epidural man]

Seitsonen ER, Yli-Hankala AM, Korttila KT. Similar recovery from bispectral index-titrated isoflurane and sevoflurane anesthesia after outpatient gynecological surgery. J Clin Anesth. 2006;18(4):272-279. doi:10.1016/j.jclinane.2005.12.005

Zuckerman R, Sakima N, Parker SD, Fleisher LA. Comparison of recovery profile after ambulatory anesthesia with propofol, isoflurane, sevoflurane and desflurane: a systematic review. Anesth Analg. 2004;98(3):. doi:10.1213/01.ane.0000103187.70627.57

Maheshwari K, Ahuja S, Mascha EJ, et al. Effect of Sevoflurane Versus Isoflurane on Emergence Time and Postanesthesia Care Unit Length of Stay: An Alternating Intervention Trial. Anesth Analg. 2020;130(2):360-366.

Long story short - there is little difference in recovery time between sevo and iso regardless of case duration. There are other variables we are neglecting when thinking about emergence time aside from the blood gas partition coefficient - namely things like the blood muscle and fat coefficients which are significant contributors to central compartment redistribution and emergence. Turns out these variables are very similar between the two gases. In these studies the difference in time to extubation was like 7 minutes or something in the worst case scenario where the gas is turned from 100 to 0 while the dressings are going on (worst case scenario.)

In addition, I understand that newer calcium based CO2 absorbant species do not appreciably at all generate compound A formation - however there's just something that gives me the heeby-jeebys about not obeying the sevoflurane FDA label's own recommendation to not run more than <2L FGF for 2MAC hour or greater cases etc.

That all being said, I feel much better about running Iso and low flows (<1L FGF) because it is better for the environment and patient (temp and humidity savings blah blah), but also I believe the cost between consumed gas and consumed absorbant sweet spot is 1L for isoflurane (and might be the same for sevo, but see above).

Wake up time is Not the only important thing.
How about how the patient feels off-gassing ISO For the next 24 hours?

I bet if you run ISO for 6 hours, and Sevo for six hours, you may be able to extubate the two within 7 minutes of each other, but would they look the same 1 hr later? I doubt it. Would they feel the same 6 hours later?

what does a low dose infusion of isoflurane feel like over several hours?

 

[coffeebythelake]

Wake up time is Not the only important thing.
How about how the patient feels off-gassing ISO For the next 24 hours?

I bet if you run ISO for 6 hours, and Sevo for six hours, you may be able to extubate the two within 7 minutes of each other, but would they look the same 1 hr later? I doubt it. Would they feel the same 6 hours later?

what does a low dose infusion of isoflurane feel like over several hours?

Is that a question or a statement? I haven't noticed a difference between sevo and iso as you are suggesting.

(Some people do wake up from TIVAs without the persistent grogginess and feeling like a million bucks.)

 

[coffeebythelake]

I pretty much only do TIVA or Iso, but I also don't spend too much time in ASCs or do high pressured outpatient procedures so they can take all the time they need to wake up in PACU in my book

What kind of cases u doing where you use TIVA so frequently

 

[epidural man]

Is that a question or a statement? I haven't noticed a difference between sevo and iso as you are suggesting.

Maybe you are right and you have observed several patients several hours after the anesthetic. In my experience when I see patients in PHASE II hours later, it seems there is a difference.

To answer you question you asked Twiggidy - I do TIVA on every case, unless a resident chooses not to, or it is a kid.

 

[coffeebythelake]

Maybe you are right and you have observed several patients several hours after the anesthetic. In my experience when I see patients in PHASE II hours later, it seems there is a difference.

I think there is so much inter-individual variability postop recovery from both sevo and iso that it would be difficult to identify a difference even in a large study. Would be an interesting one to perform though.

To answer you question you asked Twiggidy - I do TIVA on every case, unless a resident chooses not to, or it is a kid.

I feel like I do TIVA a fair amount and it is still only about 5% of my cases, mostly on severe PONV patients. What clinical effect are you targeting for? Less PONV? Less immunomodulation (questionable evidence)? Better postop course ("waking up like a million bucks" and reading the newspaper 5 minutes into PACU)? How do you justify this practice with the significantly higher cost of anesthesia (propofol bottles ain't cheap! also need for BIS monitoring!) when doing routine cases?

 

[Twiggidy]

What kind of cases u doing where you use TIVA so frequently

I prop/remi just about every general anesthetic i perform or propofol if i'm using an LMA. In a handful of cases will i go straight Iso. In most of mystery old frail peeps i'll go as low as tolerable Iso, especially my sick vascular patients. I think I honestly only use Sevo on my carotids where I kind of want them awake for a neuro exam, but you could honestly still use Iso.

 

[coffeebythelake]

I prop/remi just about every general anesthetic i perform or propofol if i'm using an LMA. In a handful of cases will i go straight Iso. In most of mystery old frail peeps i'll go as low as tolerable Iso, especially my sick vascular patients. I think I honestly only use Sevo on my carotids where I kind of want them awake for a neuro exam, but you could honestly still use Iso.

PP? Academics? Surprised pharmacy isn't all over you for using so much propofol and remi

 

[Twiggidy]

PP? Academics? Surprised pharmacy isn't all over you for using so much propofol and remi

Private practice. Our hospital cares more about patient satisfaction so if patients aren't complaining they don't care what I use or how much it costs.

 

[epidural man]

I think there is so much inter-individual variability in responses to both sevo and iso that it would be difficult to identify a difference even in a large study. Would be an interesting one to perform though.

I feel like I do TIVA a fair amount and it is still only about 5% of my cases, mostly on severe PONV patients. What clinical effect are you targeting for? Less PONV? Less immunomodulation (questionable evidence)? Better postop course ("waking up like a million bucks" and reading the newspaper 5 minutes into PACU)? How do you justify this practice with the significantly higher cost of anesthesia (propofol bottles ain't cheap! also need for BIS monitoring!) when doing routine cases?

I remember a staff telling me that people on propofol wake up happy, hungry, and horny.

I was doing some work at a plastic surgeons office and he wanted TIVA for all his cases (for patient satisfaction). I was so impressed with how well it worked and how patients felt, I thought - why in the world would I NOT do this for all my cases? He was VERY cost conscientious and made me use the worst, crappy supraglotic airways in the word. They NEVER sealed. Yet, he thought it was worth using propofol for everything.

I mix 2000mcg alfentanil in the 100ml bottle of propofol. Sometimes, I need to put 3000mcg in a bottle, I've even gone up to 4000mcg in a 100ml bottle.

Propofol isn't expensive. It actually is quit cheap these days. Alfentanil costs like 2 cents for 2500mcg. If you look at context sensitive half lives of prop and alfentanil, it is the perfect combination. Prop goes away and alfenta sticks around a little longer (but is a flat line), giving a nice combination.

Here are some medical reasons I justify using propofol.

Volatile anesthetics increase sleep deficit. Propofol actually diminishes it.

My old nemisis, stage 2, doesn't exist with propofol. I don't have to time anything. If I have turned down the infusion (I always start at 180mcg/kg/min) appropriately, people wake up quick - but if they don't, no bother...just pull the tube at any point. Patients are happy and wide awake in the PACU in a matter of minutes - no matter the length of the case (12 hrs or 1 hr).

Regarding a BIS, I'll use it if available, but it isn't needed.

 

[epidural man]

Here is perhaps one of my favorite graphs of all time.

 

[coffeebythelake]

Regarding a BIS, I'll use it if available, but it isn't needed.

Oh I agree with your thoughts, it is a great drug and personally if I needed a GA I would request one. There is a significant variability in patient responses to propofol though and I would want to BIS monitor them. Especially as Marijuana use become legalized and even more mainstream. I've had a few patients i needed more than 250 mc/kg/mjn to sedate and literally wake up 20 seconds after turning off sedation. Seems some people would be very high risk for awareness under GA with such situations

 

[coffeebythelake]

Here is perhaps one of my favorite graphs of all time.

View attachment 322059

View attachment 322060

What source is this from?

 

[epidural man]

Oh I agree with your thoughts, it is a great drug and personally if I needed a GA I would request one. There is a significant variability in patient responses to propofol though and I would want to BIS monitor them. Especially as Marijuana use become legalized and even more mainstream. I've had a few patients i needed more than 250 mc/kg/mjn to sedate and literally wake up 20 seconds after turning off sedation. Seems some people would be very high risk for awareness under GA with such situations

lots of Midazolam in daily marijuana users.

 

[epidural man]

What source is this from?

Context sensitive half time

Context-sensitive half time is the concept which relates the drug distribution into and out of tissue compartments to the change in plasma concentration after sustained infusion. If the infusion has not achieved a steady-state of concentration, the context-sensitive half time will more closely...

derangedphysiology.com

 

[propadope]

Context sensitive half time

Context-sensitive half time is the concept which relates the drug distribution into and out of tissue compartments to the change in plasma concentration after sustained infusion. If the infusion has not achieved a steady-state of concentration, the context-sensitive half time will more closely...

derangedphysiology.com

These two graphs show very different CSHT no? At 480 minutes the first graph shows 5minutes. In the second graph its around 40min. Or am I reading it wrong?

 

[zizzer]

Why do you care what the inspired agent percentage is? The exhaled is what the brain is seeing, only relevant number imo.

You're right. That's primarily what I'm interested in. I find that looking at FiSevo in conjunction with the FGF, minute ventilation, and the vaporizor setting gives me a bit more information on where EtSevo is going to go and how fast it will go there.

My old nemisis, stage 2, doesn't exist with propofol. I don't have to time anything. If I have turned down the infusion (I always start at 180mcg/kg/min) appropriately, people wake up quick - but if they don't, no bother...just pull the tube at any point. Patients are happy and wide awake in the PACU in a matter of minutes - no matter the length of the case (12 hrs or 1 hr).

Interesting. You pull the tube at any time and don't really worry much about laryngospasm or tube biting? I've never heard that. Do you do this often? Any other caveats to doing this? Does anybody else do this and want to chime in?

 

[coffeebythelake]

Interesting. You pull the tube at any time and don't really worry much about laryngospasm or tube biting? I've never heard that. Do you do this often? Any other caveats to doing this? Does anybody else do this and want to chime in?

Anecdotally it still happens but less frequently than w gas

 

[epidural man]

You're right. That's primarily what I'm interested in. I find that looking at FiSevo in conjunction with the FGF, minute ventilation, and the vaporizor setting gives me a bit more information on where EtSevo is going to go and how fast it will go there.



Interesting. You pull the tube at any time and don't really worry much about laryngospasm or tube biting? I've never heard that. Do you do this often? Any other caveats to doing this? Does anybody else do this and want to chime in?

The way I understand it, laryngospasm can happen to anyone at any time .

However, when a person is in an excitable state (STAGE 2), it is much more likely to happen.

It rarely happens under propofol.

Bitting the tube is also more common as a STAGE 2 phenomenon, but it is irrelevant to the discussion because measures to prevent this have nothing to do with the type of anesthetic I am using.

Lots of caveats and reasons not to do this, or you have to know when it wouldn't be a great idea.

 

[epidural man]

View attachment 322080
View attachment 322079


These two graphs show very different CSHT no? At 480 minutes the first graph shows 5minutes. In the second graph its around 40min. Or am I reading it wrong?

No they aren't different. CSHT and peak onset/offset are not the same thing.

 

[propadope]

No they aren't different. CSHT and peak onset/offset are not the same thing.

Can you explain the onset and offset graph and why its one of your favorites?

 

[epidural man]

Can you explain the onset and offset graph and why its one of your favorites?

Well let me say from the get go, I don’t fully comprehend the difference you point out but I think it has something to do with the idea about 3 half-life’s described for propofol (1 min, 16 min, 300 min), and that the graph I posted is a computer sim, and the graph you posted is more clinically relevant.

the reason I like the graph is it just shows what I have experienced, and not what my staff always told me, and what my colleagues believe - and that is that if I run propofol for a very long time, it doesn’t matter much...it still goes away very quickly.