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Changing agent during case

Discussion in 'Anesthesiology' started by interleukin2, 02.22.12.

  1. interleukin2

    interleukin2

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    So i take over a case and notice we are running sevo. Because its a long case and the pt is chubby. I think it may be better to change to des. Some attendings don't like nitrous. Anyways I call the tech to bring me a des vaporizer and he reacted as if I was doing something dangerous. So I asked what his concearn was and he said something like "your the doctor" and left. So I looked for any studies about possible detrimental effects and could find none. So I talked to a couple if attendings with about 40
    Yars of exp. combined and they could think of no particular
    Problems however because of the solubility of sevo in a
    Long case switching over to something
    Like des. Won't make a difference time wise. ( anesthesiology volume 88(4) april 1998 pp. 914-921) So if ur going to switch...switch at the begining So in the end I stayed and used nitrous at the end. So my question is say u run out of one gas. And switch to another mid case. Any problems to watch out for? Any increase chances of bad outcomes? Any studies? I know that anything may be possible and mixing agents may not be a great idea because if anything goes awry it can be a point of blame. But that aside. I would appreciate the input! Thanks
    Last edited: 02.22.12
  2. W222

    W222 2K Member

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    Maybe the tech was a little nervous about switching a vaporizer in the middle of a case? Thats the only thing I can think of, but changing out a vaporizer shouldn't be an issue. Other than that, no specific thing comes to mind. I personally don't like des because patients tend to go bonkers when they wakeup (especially the young males) in my experience and unless the case is relatively short (<2hours) you are not going to gain any time during wakeup. I know alot of people dont like nitrous (increased PONV, wound healing) but if you only use it for the end of the case of wakeup it is great.
  3. pgg

    pgg Laugh at me, will they? Moderator

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    Nothing wrong with switching agents. I use desflurane almost 100% of the time.

    - It doesn't cost more than sevo if you use very low flows.
    - PACU times are shorter, which matters as much as the in-OR wakeup time.
    - It's almost impossible to be really screwed by an abrupt "I'm done" from the surgeon.
    - Obese patients, ie most of them.
  4. Idiopathic

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    i use isoflurane almost exclusively. i do not like to switch agents in the middle of a case, but we have all three vaporizers in line so it really wouldnt be an issue.

    remember with desflurane that rapid adjustments can result in sympathetic stimulation (tachycardia, etc) and i have also seen this when switching agents during a case (tried the long case on iso with a "des wakeup" a few times in residency, usually turned into a disaster)
  5. WholeLottaGame7

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    I figured it was going to be this paper. If you read it critically, there are all sorts of problems. They use a whopping 5 healthy volunteers and didn't actually perform surgery on them. The "cases" were short, 2 hours total. There was no statistical difference between iso-only and crossover, but if you look at their graphs there is a trend towards shorter wake-ups. Certainly in sum not enough for me to say "oh there's no point in switching agents."

    With that in mind, I have started switching from iso to des for long cases (3 hours or so), especially for the obese and elderly. I usually switch over with about an hour left and keep the flows low (<1.5L total) and I don't see the sympathetic effects of the des since it gradually builds up and the iso gradually wears off. You do have to play around with the concentrations since the des will come on faster than the iso leaves, however.
  6. pgg

    pgg Laugh at me, will they? Moderator

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    This is true, but not really an issue if you avoid the rapid bit. :) Tube/LMA goes in, fresh gas flow to 0.5 L/min. Desflurane vaporizer to 12. ET des gradually climbs to ~6% over the 10 minutes it takes to position/prep/timeout/cut. No tachycardia.


    I used to love isoflurane wakeups. So smooth, with a good analgesic effect from the residual gas that went with them to the PACU. I got away from it mainly because the PACU stays were longer. I want my patients wide awake and comfortable upon arrival because of the long-acting opiates I gave them, not because of leftover gas effects.


    But to each his own. No wrong gas. Every resident should learn to use them all, and then I think it's totally natural that people tend to pick one and use it most of the time, unless they have a specific reason not to.
  7. michigangirl

    michigangirl

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    When I'm not in the outpatient center, I want all my residents to learn how to wake up with iso in a timely manner. I do this because they learn how to use des plenty with other attendings. So I have them use iso exclusively, because as others have said, the wake up is just splendid if the timing is right. I also like nitrous, so this makes things a little easier. Although I can't see any major reasons not to switch to des at the end of the case unless the sympathetic stim becomes an issue. The tech probably didn't want to change out vaporizers in the middle (not sure why though) I generally don't like to change to des at the end because i do kids and I induce with sevo, use iso for the case, three different agents just seems unnecessary and muddles things even more.
  8. fakin' the funk

    fakin' the funk CA-2

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    Just to reiterate the idea that "there is no wrong gas," you could also argue that LONG cases is exactly when you SHOULD use a highly insoluble agent like des, so that you can actually get a benefit of its relatively quicker offset.
  9. Mman

    Mman Senior Member

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    I have no real preference for any gas over any other, except Iso with low flows is by far the most cost efficient. And if you can't wake up a 6 hour case on a dime with iso, then you need more practice with it.

    We tend to use des more on our gastric bypass population (mostly 300-500 lbs).
  10. soonerfrog

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    Not starting an argument, but would you agree you're getting extra sedative/hypnotic effect from the Iso owing to its higher solubility, not any extra analgesia? Although the net effect is markedly similar.
  11. Mman

    Mman Senior Member

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    correct. the patients complain of less pain because they are not as awake. It doesn't lower their narcotic requirements, just prolongs the time until they need those narcotics.
  12. BLADEMDA

    BLADEMDA SDN Gold Donor Gold Donor

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    If you switch agents with over an hour to go in the case the newer agent, desflurane, should be the only agent left at the end of the case. The reason switching agents ussli doesn't do much is because the switch occurs near the end of the case (less than 30 minutes to go) so the primary agent is still being exhaled and redistributed from the fatty tissues.

    A good study looking at wake up times in long cases (4 hours or longer) where the agent was switched at 1, 2 and then the third hour into the case would be quite interesting.
  13. nap$ter

    nap$ter SDN Bronze Donor Bronze Donor

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    just curious - do you think this is any different from leaving the flow at 1 and the dial at 6 for 10m?
  14. pgg

    pgg Laugh at me, will they? Moderator

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    Sure, probably both. Which again is why I'm less enthusiastic about nice smooth iso wakeups now than I used to be. On the extreme end, it's as if the PACU admission (awake gas-free patient) occurs 10 minutes later. Unless I'm deliberately planning on emergence in the PACU (eg deep extubations), it doesn't make a lot of sense to me to head to PACU with an ultra-short-acting analgesic (gas) that will be gone soon after I drop off the patient, leaving the PACU nurse to start at square 1 with pain meds and more monitoring time.

    It's the same reason I prefer to top patients off with morphine or Dilaudid at the end of a case, not fentanyl.


    Yes. 1 lpm at 6% will never get the end-tidal des above 6%. The rate of ET-des change is also different. A faster rise initially, and slower rise as it approaches 5-6%. The lower fresh gas flow produces a more gradual, constant rise in end-tidal gas with a higher ceiling.

    This is a good read:

    http://etherweb.bwh.harvard.edu/education/PHILIP/Tech_Block_04/1_LowFlowO2Agt.pdf
  15. interleukin2

    interleukin2

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    I agree, and as I become more comfortable with the flow of the OR I am setting small goals for myself ie. When I work at out OP center my goal is to tailor my anesthetic plan to the goal fo going home, with inpatient cases it differs a bit. Because in academic settings things seem to move a tad slower than in PP I think it would be a good time to practice smooth and quick wakeups with iso and agent I feel we dont us much anymore except for special cases ie cardiac. What are some tips for working with iso? how do you approximate the time to wakeup and balance that with the need to keep patient recall and/or movement at bay?
  16. ssmallz

    ssmallz California Dreamin

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    Actually it's the exact opposite. If you look at the wake up time differences between des, sevo, and iso, the short cases don't have much differences in terms of absolute mintues to wake up. It's the really long cases where solubility makes a difference. One could argue that when doing shorter cases the relative wake up time of cutting a few minutes to wake up in the PACU is important but those patients tend to wake up quickly anyways and leave the PACU very quickly so I don't think it matters if you save 2 or 3 mintues on the wake up. Longer cases with more soluable agents lead to sleepy patients in the PACU, that's where des really shines
  17. btbam

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    As others said, it was probably the fact that the tech felt uncomfortable changing out vaporizers in the middle of the case. We don't even have des at our hospital :eek:
  18. BLADEMDA

    BLADEMDA SDN Gold Donor Gold Donor

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    Correct. The question still remains can you use ISO for the first 3 hours of a 4 hour case then switch to DES and get that great, speedy wake-up.
  19. dr doze

    dr doze Neocon Gold Donor

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    Yes, if you have a high enough flow to negate the effects of rereathing iso. Of course having high flow with des defeats the cost saving motivation of using iso for the first 3 hours.
  20. Impromptu

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    I don't have too much experience with this concept, but I took over a long ENT bilateral neck dissection and free flap case. The prior resident had switched to des from iso, which turned out to be with about 4 hours left in the case. Des was at about 1.3 MAC at low flows. Time to wake-up at the end was still pretty long. Des still had to redistribute out from all the fat, though probably not as long as iso would have taken.
  21. DO Anes

    DO Anes ASA Member

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    http://www.anesthesia-analgesia.org/content/101/3/688/F1.expansion.html
    It depends on "awake". Simple opening of eyes and response to command can occur at 80% decrement, but more soluble agents, including sevoflurane (high tissue solubility), leave patients "drunk" for prolonged periods, depending on case length. 90% or greater decrement is required for fine neuropsychiatric functioning. Note that the 90% decrement graph for desflurane is mathematically a flat-line relationship, implying far less tissue accumulation and no increase in 90%DT regardless of case duration, hence the advantage of des, especially in cases >60 min relative to sevo or >30 min, relative to iso. (Of course, there are a lot of other reasons not to use sevo, but I digress). Since the fat is vessel poor, the sevo/iso enters extremely slowly and then exits equally slowly (i.e. over the next few days).
    Last edited: 02.23.12
  22. BLADEMDA

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    Thanks for the basics:cool: you have no idea how long the ISO can be on before switching to DES for a speedy wake up. My hunch is that 2 hours with the ISO off is enough time to get that agent out of even the fatty vessels/tissue. I'm willing to be that on a long case even with very low flow if the last 2 hours of the case is DES only the wake up will be speedy. But, what about 90 min? 1 hour? I'm less certain at those time frames.

    This is why we do studies for evidence based medicine.
  23. pgg

    pgg Laugh at me, will they? Moderator

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    Although academically interesting, whether it's 60 or 90 or 120 minutes is a distinction with dubious practical value. I think this bears repeating:

    If you want a desflurane wakeup, just use desflurane from the start. Set the O2 knob at 0.4 or 0.5 lpm, maybe add 0.05 or 0.1 lpm of air if you don't want an FiO2 of 90+, and be done with it.

    We ought to add "deflurane is expensive" to the latest dogma thread.
  24. dr doze

    dr doze Neocon Gold Donor

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    It is just that I have done a few long cases with residents who had iso on for the first few hours with low flow (for economy), turn on des for the last hour or two and maintain low flow, and were surprised that at wakeup the agent monitor showed a concentration of iso even after des being undetectable.
  25. BLADEMDA

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    The thing is I run 0.5 liter of O2 and 0.3 L of Air with isoflurane on long cases. I turn off the vapor appropriately and use my monitors for expired vapor. This means my wake ups are pretty fast even with ISO. That said, Pacu stay may be shorter with Des.
  26. BLADEMDA

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    Exactly. That's why a study would be very interesting to see if that last bit of remaining ISO affected PACU discharge time. Wake up should still be fast because residual ISO after 2 Hours (low flow) shoud be less than 0.2 expired
  27. btbam

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    Blade if you are going to run really low flows like 0.2 and 0.2, what do you set the Iso vaporizer dial at? I am not great at understanding the correlation between super low flows as it relates to the numbers on your monitor vs. dial settings...
  28. pgg

    pgg Laugh at me, will they? Moderator

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    I was agreeing with you. :) Switching doesn't make sense if the goal of using iso was cost reduction, because as you said, in order to wash out the iso, you need not-low flows of des.


    Anecdotally it is in my experience, and of course the Desflurane rep used to claim that over free sandwiches ... If someone wanted to do a non-Suprane-funded study of PACU times, I'd read it.
  29. Idiopathic

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    enough to achieve the desired end tidal agent concentration?

    the powerpoint quoted above is a great example of how to do low flows with desflurane, it works fine. i think you will have trouble achieving rapid anesthetic level with low flow iso from the start (whereas the author above advocates starting with 0.5L/m O2 and 18% des - i dont think you could argue the same would work for a more soluble vapor), so i think you would have to allow for high flows up front, and then titration down to a low flow state.
  30. Idiopathic

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    oh and remember you will typically need at least 250cc/min of O2 for human oxygen consumption, and will then need to account for your gas samplingline (another 50cc/min?) so most of us wont go lower than 0.4-0.5L/min O2, whether or not we add air.
  31. Mman

    Mman Senior Member

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    With Iso you can just start with 1 L flows and the vaporizer at 3 or 4 for a few minutes and then dial your flows back.

    I'd usually end up with 0.2 oxygen and 0.1 air with the vaporizer dial around 2.5 or 3 for most of the case. Remember the patient is probably consuming 200-250 ml of oxygen per minute so there is only so low you can get the O2 flows down to. You can almost just run 0.3 l/min of oxygen and no air and get a reasonable mix.
  32. BLADEMDA

    BLADEMDA SDN Gold Donor Gold Donor

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    You are quite the penny pincher!;) ISO is dirt cheap. I start with 2 liter flows for the first 10 minutes then dial down to 0.5 O2 and 0.3 or 0.4 air. I'm pretty sure that is very efficient use of generic ISO. CAn you go lower? Yes. Would I want my CRNAS dialing in less than 0.5 O2...No.

    With DES going extremely low (0.3 or 0.4 O2) at least makes economic sense; with ISO I just don't see how that 50 cents savings matters on a $30K operation.
  33. BLADEMDA

    BLADEMDA SDN Gold Donor Gold Donor

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    Cost per milliliter. Desflurane, sevoflurane and isoflurane vary widely in price. My calculations for the cost of these drugs last month (based on the Federal 340B drug pricing program) had isoflurane as the cheapest at about $12 per 250ml bottle, compared to sevoflurane at $67 per 250ml bottle and desflurane, the priciest, at $148 per 240ml bottle.
  34. BLADEMDA

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    I think we get our ISO for $8-$9.00 per 250 ml bottle. So I'm not sure why you need less than 0.5 O2 flows at that price.

    I do like getting the CRNAS in the habit of low gas flow anesthesia. Hence, I encourage low flow with all our agents especially DES. ( I don't want to get into a debate on SEVO at less than 2 liters flow for long cases here).
  35. pgg

    pgg Laugh at me, will they? Moderator

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    How old is that quote? I'll check on Monday but I know we don't pay anywhere near $148/bottle for desflurane.
  36. DO Anes

    DO Anes ASA Member

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    Exactly. No studies support the hunch. In fact, the few studies that have been done demonstrate the opposite. You can't have your cake and eat it too.
    Of course, all this debate is emblematic of the subordinate posture we in anesthesia quickly jump to. We run extreme low flows, switch agents, etc. to save a few relative cents for extremely expensive surgeries. If a surgeon drops a stapler on the floor it costs a thousand dollars, but they don't seem to stay up late worrying about it, they just ask for another GIA/octopus/whatever (insert latest expensive toy here).
  37. BLADEMDA

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    Agree. These are major, expensive surgeries in the tens of thousands of dollars. Run all the DES you want to.
  38. WholeLottaGame7

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    What do efficiency and financial responsibility have to do with subordination?
  39. DO Anes

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    Anesthesia is not a contest of skills. It is doing the most safe and best anesthetic every time for each individual patient. Des offers substantial advantages in many patients. Extreme low flows are inherently less safe than higher (1 lpm) flows. We sometimes avoid des and use these low flows in the name of "efficiency and financial responsibility". Of course this ignores the whole issue of throughput, OR/PACU time and long-term neuropsychiatric sequelae because of a <1% savings for a line item.
    When was the last time a surgeon didn't use a disposable because it was too expensive?
  40. pgg

    pgg Laugh at me, will they? Moderator

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    How's that?
  41. Mman

    Mman Senior Member

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    I agree. Since when is being cost efficient less safe when it comes to low flows? I monitor the FiCO2 and ETCO2 so I can tell when the absorbent is cooked.

    I'm pretty sure the rest of the world appreciates less greenhouse gas emissions than having the flows cranked up and sucking the gas out the scavenging system.
  42. BLADEMDA

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  43. BLADEMDA

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    Are you all running low flow (1 liter or less) for long cases greater than 4 hours with SEVO?

    "Postoperative renal function after long-duration low-flow sevoflurane (with Compound A exposures greater than those typically reported) and isoflurane anesthesia were not different, as assessed by serum creatinine, blood urea nitrogen, and urinary excretion of protein and glucose. This suggests that low-flow sevoflurane is as safe as low-flow isoflurane, even at long exposures. "

    http://www.anesthesia-analgesia.org/content/93/6/1511.short
  44. BLADEMDA

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    "We conclude that prolonged low-flow sevoflurane anesthesia has the same effect on renal and hepatic functions as high-flow sevoflurane and low-flow isoflurane anesthesia. Implications: During low-flow sevoflurane anesthesia, intake of Compound A reached 277 +/- 120 ppm-h, but the effect on the kidney and the liver was the same in high-flow sevoflurane and low-flow isoflurane anesthesia."

    http://www.ncbi.nlm.nih.gov/pubmed/11049919
    Last edited: 02.26.12
  45. BLADEMDA

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    Remember the package insert from the FDA for SEVO still clearly warns against the use of low flow (less than 2 liters) in cases where greater than 2 MAC hours are required.

    Hence, I'd rather not use low flow in Critically ill patients, Renal Disease or Hepatic disease.

    What's your opinion?
  46. BLADEMDA

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    In summary, the available information indicates that all durations and depths of sevoflurane anesthesia are nontoxic to the normal human kidney as long as exposure to Compound A is kept below <150 ppm-h. Significant questions persist, however, regarding the potential for Compound A to cause renal injury at larger doses and whether transient albuminuria, glucosuria, and/or enzymuria reflect pathological changes (renal injury) or functional abnormalities. Does the usually mild and transient nature of the changes indicate that they are not clinically relevant? Need the practitioner consider the possibility that insults to the kidney may have a cumulative effect that may not be apparent in one or two exposures? Are particular patients more vulnerable to greater degrees of injury? Answers to these questions await further investigation.


    http://www.anesthesia-analgesia.org/content/90/3/505.full
  47. pie944

    pie944 ASA Member

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    You can use Amsorb "Plus" for the carbon dioxide absorbent and this does not produce any Compound A. So at our institution we switched over to that and people can run low flows with Sevoflurane regardless of case duration.
  48. BLADEMDA

    BLADEMDA SDN Gold Donor Gold Donor

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    We priced Amsorb Plus using 1 liter SEVO flow rates vs. Standard CO2 absorbent with 2 liter flows and decided it was cheaper to buy the Standard absorbent.
  49. BLADEMDA

    BLADEMDA SDN Gold Donor Gold Donor

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    According to the guideline, soda lime (Spherasorb, Intersurgical, United Kingdom) was changed weekly on Mondays [11]. Amsorb Plus was changed once uniform colour change happened. Both were changed if inspired CO2 &#8201;&#8201;occurred with total fresh gas flow of 4&#8201;L/min or more. Low flows (<2&#8201;L/min) were encouraged with Amsorb Plus, while flows of between 2 and 4&#8201;L/min were advised with soda lime. End tidal agent monitoring was performed in all patients.


    http://www.isrn.com/journals/anesthesiology/2011/730483/
  50. BLADEMDA

    BLADEMDA SDN Gold Donor Gold Donor

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    Amsorb Plus (Armstrong Medical Ltd., Coleraine, Northern Ireland) is a novel CO2 absorber introduced by Murray et al. in 1999, that does not contain strong alkalis and so does not have these drawbacks [1, 10]. However, it is more expensive per unit weight than soda lime. This cost might be offset by lower sevoflurane use as there is no risk of compound A formation at lower flows permitting fresh gas flows of 2&#8201;L/min or less-fewer product changes are required as the colour change is uniform and stable, and there is cheaper waste disposal as Amsorb Plus is inert and can be disposed off in domestic waste rather than soda lime which is disposed of in health care waste. There are also no concerns with its handling, unlike for soda lime which is caustic.
    Many studies have compared Amsorb Plus to conventional soda lime in terms of efficiency and safety regarding the production of compound A and carbon monoxide [1, 9, 10]. However, none has investigated the cost implications of replacing soda lime with Amsorb Plus in daily clinical practice.

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