Menu Icon Search
Close Search

About the ads

Flow Rates

Discussion in 'Anesthesiology' started by drccw, 12.07.09.

  1. drccw

    drccw

    Joined:
    01.20.08
    Messages:
    318
    SDN 5+ Year Member

    SDN Members don't see this ad. (About Ads)
    Just curious what fresh gas flows do you guys typically use:
    I'm at 0.5 L/min.. for all my anesthestics (we have a choice of Sevo or Des).

    From what I've seen around our practice, most people are 1 L/min for Des, 2 L/min for Sevo... though we have one CRNA who is at 2 L/min for Des (he happens to date a Baxter rep....)

    So what are people doing?
  2. rsgillmd

    rsgillmd

    Joined:
    11.24.07
    Messages:
    697
    Status:
    Attending Physician
    SDN 5+ Year Member
    With Des 0.5 L/min with me. 1 L/min with most of the CRNAs.

    With Sevo less than 2 hrs case 1 L/min, and 2 L/min if I expect it to be a longer case. I think higher flows are required after 2 hours for Sevo if I recall my textbooks correctly.

    2 L/min for Des (other than running high flows to build it up quickly) is like pouring it down the drain.

    Where I trained one of our machines had a low flow wizard. I noticed once I had an acceptable end tidal I never needed to go above 0.45 L/min. I pick 0.5 L/min to buy myself a small safety margin, and because it's easier to look at.
  3. BLADEMDA

    BLADEMDA SDN Gold Donor Gold Donor

    Joined:
    04.22.07
    Messages:
    11,618
    Location:
    Southeast
    Status:
    Attending Physician
    SDN 7+ Year Member
    Ask yourself WHY people are using 2 liters per minute total flow for Sevoflurane. Do you believe in that theoretical risk to the kidneys at less than 2 liter flow for a short case? What about long cases?

    Since you use 0.5 liters per minute total flow how much lower could one go? What are the disadvantages to extremely low flow anesthetics in a semi closed system? Does the type of case or weight of the patient affect your total flow?

    Good topic but one that is more complicated than the surface may reveal.
  4. Bertelman

    Bertelman Maverick!

    Joined:
    02.11.06
    Messages:
    4,213
    Location:
    Had a Cooch
    Status:
    Attending Physician
    SDN 7+ Year Member
    1 L/min.

    If the case is longer than 2 hrs, I'm not using sevo.
  5. Planktonmd

    Planktonmd Moderator Emeritus Lifetime Donor

    Joined:
    11.02.06
    Messages:
    4,982
    Location:
    The South
    Status:
    Attending Physician
    SDN 7+ Year Member
    Why not?
  6. SleepIsGood

    SleepIsGood Support the ASA !

    Joined:
    04.15.06
    Messages:
    1,968
    Status:
    Fellow [Any Field]
    SDN 5+ Year Member
    Your flow, atleast the O2 flow should be based on O2 consumption....about 3 ml/kg/min on the higher side...or titrate to your pulse ox...that's how much flow you really need.
  7. checkov

    checkov

    Joined:
    11.24.09
    Messages:
    71
    Status:
    Resident [Any Field]
    SDN 2+ Year Member
    Interesting topic. Bump on Planktonmd's question.

    Is there a citation / anecdotal evidence that sevoflurane is relatively contraindicated if a case is slated to be longer than 2 hours?

    There's a paper by Kharasch that states that "prolonged (8 h), high concentration (3%) sevoflurane anesthesia administered to volunteers in a fresh gas flow of 2 l/min does not result in clinically significant changes in biochemical markers of renal or hepatic dysfunction." [Anesthesiology, March 1998]
  8. drccw

    drccw

    Joined:
    01.20.08
    Messages:
    318
    SDN 5+ Year Member
    I use 0.5 L/m because I am too chicken to use 0.3 L/m... I find that at rates lower than 0.5 then there is some variability (ie the flow rate at 0.3 mysteriosuly drops to 0.2). 0.5 L/min seems to give me more than enough cushion for error... that should be more than enough oxygen for the average human's consumption.

    As for Sevo- I feel like it's a conspiracy, the recommended flow rates- it's to get you to use more...Kind of the like the back box warning on droperidol (so you use more odansetron)... compound A? show me some evidence that it's clinically significant. I anesthetize humans, not rats (even though some might be the lowest level of human...) I asked a CRNA the other day why he was running Sevo at 2 L/m-> he replied because of Compound A and the risk of renal toxicity... his patient was HD dependent...
  9. Planktonmd

    Planktonmd Moderator Emeritus Lifetime Donor

    Joined:
    11.02.06
    Messages:
    4,982
    Location:
    The South
    Status:
    Attending Physician
    SDN 7+ Year Member
    Low flow anesthesia is very nice and elegant especially for long cases.
    You should not be afraid of trying closed circuit anesthesia as well where you drop the flow to around 200-250 ml/min of oxygen, close your pop off valve, turn off the vapor, and let the patient breath spontaneously.
    I also agree that renal toxicity with sevo at low flow is more of a theoretical concern without evidence in humans, but the manufacturer still displays it on the box which makes many people uncomfortable.

  10. BLADEMDA

    BLADEMDA SDN Gold Donor Gold Donor

    Joined:
    04.22.07
    Messages:
    11,618
    Location:
    Southeast
    Status:
    Attending Physician
    SDN 7+ Year Member
    Acta Anaesthesiol Scand. 2009 Nov;53(10):1348-53. Epub 2009 Jun 30.
    Low-flow anaesthesia at a fixed flow rate.

    Cherian A, Badhe A.
    Department of Anesthesiology and Critical Care, Jawaharlal Institute of Post graduate Medical Education and Research, Pondicherry, India. [email protected]
    AIMS AND OBJECTIVES: This study attempts to assess the safety of low-flow anaesthesia (LFA) at fixed flow rates with particular reference to the incidence of a decline in FiO(2) below safe levels of 0.3 and to determine whether LFA can be used safely in the absence of an FiO(2) monitor. METHODS: A total of 100 patients undergoing procedures under general anaesthesia at fresh gas flows of 300 ml/min of O(2) and 300 ml/min of N(2)O were monitored while maintaining the dial setting of isoflurane at 1.5% for 2 h. The changes in gas composition were analysed and even a single recording of FiO(2) of <0.3 was considered sufficient to render the technique unsafe in the absence of gas monitors. RESULTS: The lowest recorded value of FiO(2) was 31% (v/v%). There was no incidence of adverse events necessitating the conversion from low flows to conventional flows. CONCLUSIONS: We conclude that low flows of 300 ml/min of N(2)O and 300 ml/min of oxygen can be used safely for a period of 2 h without the use of monitors for gas analysis of oxygen and agent in adult patients weighing between 40 and 75 kgs.
  11. BLADEMDA

    BLADEMDA SDN Gold Donor Gold Donor

    Joined:
    04.22.07
    Messages:
    11,618
    Location:
    Southeast
    Status:
    Attending Physician
    SDN 7+ Year Member
    Acta Anaesthesiol Scand. 2007 Mar;51(3):290-3. Epub 2007 Jan 23.
    The effects of fresh gas flow on the amount of sevoflurane vaporized during 1 minimum alveolar concentration anaesthesia for day surgery: a clinical study.

    Ekbom K, Assareh H, Anderson RE, Jakobsson JG.
    Department of Pediatrics, Karolinska University Hospital, Stockholm, Sweden.
    BACKGROUND: Even small costs per case can become economically significant in high volume day surgical units. While general anaesthesia with higher fresh gas flow rates has technical advantages, they result in higher costs. The aim of the present study was to evaluate drug consumption and direct costs related to variations in the fresh gas flow and use of nitrous oxide at a 1 minimum alveolar concentration (MAC) sevoflurane end-tidal anaesthesia for day surgery. METHODS: Thirty-two ASA I-II patients undergoing elective day surgery under general anaesthesia [14 (10-21) min] were studied. Induction was with propofol and fentanyl 100 microg. After laryngeal mask airway placement, patients were randomized to one of four different fresh gas flows: 1 or 2 l/min oxygen in air (50% oxygen), 3 l/min (33% oxygen), or 3 l/min oxygen in nitrous oxide (33% oxygen). Anaesthesia was maintained at 1 MAC. The vaporizer was weighed before and after each procedure. The primary study variable was the sevoflurane utilization per minute. RESULTS: Sevoflurane utilization increased with increasing fresh gas flow for oxygen in air (r2 = 0.89). The nitrous oxide in oxygen group had the lowest sevoflurane utilization, even compared with the lowest oxygen in air group (0.36 vs. 0.48 g/min). CONCLUSION: Sevoflurane utilization during 1 MAC anaesthesia increases linearly with fresh gas flow and is still higher than when nitrous oxide is used even with very low fresh gas flow rates. Direct inhaled anaesthesia-related costs are consequently 20% higher than when nitrous oxide is used, even for the lowest oxygen in air fresh gas flows.

    PMID: 17250746 [PubMed - indexed for MEDLINE]
  12. BLADEMDA

    BLADEMDA SDN Gold Donor Gold Donor

    Joined:
    04.22.07
    Messages:
    11,618
    Location:
    Southeast
    Status:
    Attending Physician
    SDN 7+ Year Member
    Anesthesiology. 2002 Sep;97(3):578-84.
    Low-flow sevoflurane compared with low-flow isoflurane anesthesia in patients with stable renal insufficiency.

    Conzen PF, Kharasch ED, Czerner SF, Artru AA, Reichle FM, Michalowski P, Rooke GA, Weiss BM, Ebert TJ.
    Department of Anesthesiology, Ludwig-Maximilians-University, Munich, Germany. [email protected]

    Comment in:

    BACKGROUND: Sevoflurane is degraded to compound A (CpA) by carbon dioxide absorbents containing strong base. CpA is nephrotoxic in rats. Patient exposure to CpA is increased with low fresh gas flow rates, use of Baralyme, and high sevoflurane concentrations. CpA formation during low-flow and closed circuit sevoflurane anesthesia had no significant renal effects in surgical patients with normal renal function. Preexisting renal insufficiency is a risk factor for postoperative renal dysfunction. Although preexisting renal insufficiency is not affected by high-flow sevoflurane, the effect of low-flow sevoflurane in patients with renal insufficiency is unknown. METHODS: After obtaining institutional review board approval, 116 patients with a stable preoperative serum creatinine concentration 1.5 mg/dl or greater were assessable. Patients were randomized to receive either sevoflurane (n = 59, 0.8-2.5 vol%) or isoflurane (n = 57, 0.5-1.4 vol%) at a fresh gas flow rate of 1 l/min or less. Use of opioids was restricted to a minimum, and Baralyme was used to increase CpA exposure. Inspiratory and expiratory CpA concentrations were measured during anesthesia. Renal function (serum creatinine and blood urea nitrogen, urine protein and glucose, creatinine clearance) was measured preoperatively and 24 and 72 h after induction. RESULTS: Demographic patient data did not differ between groups. Patients received 3.1 +/- 2.4 minimum alveolar concentration-hours sevoflurane or 3.8 +/- 2.6 minimum alveolar concentration-hours isoflurane (mean +/- SD). Durations of low flow were 201.3 +/- 98.0 and 213.6 +/- 83.4 min, respectively. Maximum inspiratory CpA with sevoflurane was 18.9 +/- 7.6 ppm (mean +/- SD), resulting in an average total CpA exposure of 44.0 +/- 30.6 ppm/h. There were no statistically significant changes from baseline to 24- and 72-h values for serum creatinine or blood urea nitrogen, creatinine clearance, urine protein, and glucose, nor were there significant differences between both anesthetics. CONCLUSION: There were no statistically significant differences in measured parameters of renal function after low-flow sevoflurane anesthesia compared with isoflurane. These results suggest that low-flow sevoflurane anesthesia is as safe as low-flow isoflurane and does not alter kidney function in patients with preexisting renal disease.

    PMID: 12218523 [PubMed - indexed for MEDLINE]
  13. BLADEMDA

    BLADEMDA SDN Gold Donor Gold Donor

    Joined:
    04.22.07
    Messages:
    11,618
    Location:
    Southeast
    Status:
    Attending Physician
    SDN 7+ Year Member
    Compound A formation is greater with lower fresh gas flow rates, larger sevoflurane concentrations, and use of barium hydroxide lime as compared with soda lime (8). Numerous clinical investigations have evaluated Compound A formation and postoperative renal function after low-flow and closed-circuit sevoflurane, in which maximum inspired Compound A concentrations typically averaged 8–24 ppm and 20–32 ppm with soda lime and barium hydroxide lime, respectively (9–16). Compound A exposures (AUCinsp) in these investigations averaged 65 (12), 67 (9), 79 (15), 120 (10), 124 (14), 192 (16), 250 (11), and 260 (13) ppm · h. Most of these investigations evaluated standard clinical measures of renal function (creatinine clearance, serum creatinine, and BUN) and found no clinically significant effect of low-flow sevoflurane on renal function in surgical patients (9–16), as did others in which Compound A was not measured (17,18). Because proteinuria, glucosuria, and enzymuria are more sensitive than serum BUN and creatinine in detecting Compound A nephrotoxicity in rats (3,5,19), interest arose in applying these biomarkers in humans. Using these theoretically more sensitive, although clinically unvalidated, markers of perioperative renal tubular integrity (20,21), two initial investigations found no significant renal effect of low-flow (1 L/min) sevoflurane, assessed with both conventional and experimental markers of renal toxicity (14,15). Low-flow sevoflurane was considered as safe as low-flow isoflurane (14,15,21). The Food and Drug Administration subsequently permitted a change in the sevoflurane labeling, from a recommended lower limit of 2 to 1 L/min, but with a 2 minimum alveolar anesthetic concentration-hour (MAC-h) maximum exposure (because of a lack of data under the latter con-ditions
  14. BLADEMDA

    BLADEMDA SDN Gold Donor Gold Donor

    Joined:
    04.22.07
    Messages:
    11,618
    Location:
    Southeast
    Status:
    Attending Physician
    SDN 7+ Year Member
    I apologize for the literature posts. But, it is important to realize that the FDA uses TWO MAC HOURS at 1 liter flows; for many cases we are using more than ONE MAC of SEVO so the time limit will be less than 2 hours.
  15. coprolalia

    coprolalia Bored Certified

    Joined:
    08.05.07
    Messages:
    3,088
    Location:
    Paradise
    Status:
    Attending Physician
    SDN 2+ Year Member
    Rack 'em up! :laugh:

    -copro
  16. BLADEMDA

    BLADEMDA SDN Gold Donor Gold Donor

    Joined:
    04.22.07
    Messages:
    11,618
    Location:
    Southeast
    Status:
    Attending Physician
    SDN 7+ Year Member



    WARNINGS: Previous text deleted and replaced with - "Findings taken from volunteer and patient studies confirmed the potential for renal injury associated with sevoflurane. This potential is greatest when sevoflurane is administered for more than 2 MAC-hours and fresh gas flow rates of 1 L/minute to minimize exposure to compound A. Because of the findings in clinical studies, exposure at 1 L/minute flow gas flow rates should not exceed 2 MAC-hours. Fresh gas flow rates <1 L/minute are not recommended.
    "Sevoflurane should be used with caution in patients with renal insufficiency (creatinine >1.5 mg/dl).
    "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. During sevoflurane anesthesia the clinician should adjust inspired concentrations and fresh gas flow rate to minimize exposure to compound A.
    <FONT face=Arial size=2>"Sevoflurane may be associated with glycosuria and proteinuria when used in long procedures at low flow rates. The safety of low flow sevoflurane on renal function was evaluated in patients with normal preoperative renal function. One study compared sevoflurane (N=98) to an active control (N=90) administered for > or = to 2 hours at a fresh gas flow rate of
  17. dhb

    dhb Member Lifetime Donor

    Joined:
    07.12.06
    Messages:
    2,592
    Status:
    Attending Physician
    SDN 7+ Year Member
    1L/min whether Des or Sevo but i find myself using less and less Sevo. With that said i should probably be going lower on the flow rate to 0.5L/min.

    From what i can remember the problem with the low flows is the heating of the soda lime which leads to compound A formation. Anyway no significance in humans at this point...
  18. Mofeen

    Mofeen ASA Member

    Joined:
    01.29.09
    Messages:
    73
    Status:
    Attending Physician
    SDN 5+ Year Member
    We have all three agents available, as well as one attending with a few bottle stash left of Halothane, but I find myself using Iso more and more often as I progress through residency. Not sure why?????? Weird.
  19. veetz

    veetz Member

    Joined:
    10.11.04
    Messages:
    248
    Location:
    TX
    Status:
    Attending Physician
    SDN 7+ Year Member
    We're encouraged to use Iso for longer cases b/c its significantly cheaper than Sevo or Des. That aside, it's my favorite agent for now.
  20. militarymd

    militarymd SDN Angel

    Joined:
    12.17.03
    Messages:
    5,883
    Status:
    Attending Physician
    SDN 10+ Year Member
    So in a room with a 5 hour case...you are encouraged to use Isoflurane because it is "cheaper"....a long case where the benefits of using agents like sevo/des is really significant.


    BUT...

    in a room with 5 different 1 hour long cases....where total anesthesia time is the same as the one 5 hour case....where the benefits of using less soluble, more "expensive" agents are less significant....you are told that it is OK to use the more "expensive" agents.

    perfect logic.
  21. SleepIsGood

    SleepIsGood Support the ASA !

    Joined:
    04.15.06
    Messages:
    1,968
    Status:
    Fellow [Any Field]
    SDN 5+ Year Member
    I find myself using Des for those long da vinci cases, etc. for the reasons you mentioned.

    However, I think I should be using Iso. I think towards the end, perhaps when there's only 10 min left, just turn EVERYTHING off, cept O2 and some N20. I think clinically there's no difference.

    The catch is in a training program...when do you know there's only 10 min left. That's what the N2o is for...
  22. sevoflurane

    sevoflurane Ride

    Joined:
    07.16.03
    Messages:
    3,593
    Status:
    Attending Physician
    SDN 10+ Year Member
    I love low flows. Especially in hypothermic patients. Rebreathing humidified gases really can help out if your patient comes in hypothermic at baseline and then is exposed to a cold body prep. Nothing worse than waking up cold after a case. I know I would hate it.

    I close off my pop off valve and run at .3 L/M O2 and .1 L/M ox or n20. I start with higher flows/conc. sevo if healthy. Then I switch to Des and let it build up. Or give good narc/amnestic or whatever potion and let it build up from the beginning. Of course this is generic, and is adjusted according to every patient. Always start with sevo with the kids yet as of a year ago, I am still waking up with des.
  23. sevoflurane

    sevoflurane Ride

    Joined:
    07.16.03
    Messages:
    3,593
    Status:
    Attending Physician
    SDN 10+ Year Member
    Wasn't that original study that recommended 2 L/M for sevoflurane a study on rats????
  24. dhb

    dhb Member Lifetime Donor

    Joined:
    07.12.06
    Messages:
    2,592
    Status:
    Attending Physician
    SDN 7+ Year Member
    Why do you need to close th pop off valve for this?
  25. ssmallz

    ssmallz California Dreamin

    Joined:
    09.25.08
    Messages:
    631
    Location:
    SoCal
    Status:
    Fellow [Any Field]
    SDN 5+ Year Member
    For you guys running .5L/min total flows, what is your mix of O2 and air or nitrous? I would think you'd want to keep the FiO2 low as to prevent absorption atelectasis especially in a long case. Thoughts?
  26. militarymd

    militarymd SDN Angel

    Joined:
    12.17.03
    Messages:
    5,883
    Status:
    Attending Physician
    SDN 10+ Year Member
    what's that?

    I use 100% O2 almost all the time.
  27. dhb

    dhb Member Lifetime Donor

    Joined:
    07.12.06
    Messages:
    2,592
    Status:
    Attending Physician
    SDN 7+ Year Member
    100% O2 at .25ml/min doesn't give you a FiO2 of 1 (i assume you know this :D )

    What causes the atelectasis seen after induction with 100% O2 if it's not the so called absorbtion atelectasis?
  28. militarymd

    militarymd SDN Angel

    Joined:
    12.17.03
    Messages:
    5,883
    Status:
    Attending Physician
    SDN 10+ Year Member
    The same thing that causes atelectasis after induction with 21% O2.
  29. sevoflurane

    sevoflurane Ride

    Joined:
    07.16.03
    Messages:
    3,593
    Status:
    Attending Physician
    SDN 10+ Year Member
    Gas conservation, humidity retention, warmth, decreasing environment pollution and depending on your flows... a small amount of peep.

    The APL allows the user to select and change the force required to open that valve and adjust the pressure required within the patient breathing circuit to open the valve to vent the patient breathing circuit. In very low flows... you do not actually build up a significant amount of pressure with the APL in it's fully closed position. You can actually calculate the minute ventilation/O2 consumption of a particular patient in Kgs. and use this to calculate your L/M and get close to a closed circuit. One of our attendings used to make us calculate this residency. He then made us go through the exercise of calculation how much agent we used and how much we saved.:D
  30. sevoflurane

    sevoflurane Ride

    Joined:
    07.16.03
    Messages:
    3,593
    Status:
    Attending Physician
    SDN 10+ Year Member
    duplicate
    Last edited: 12.09.09
  31. pgg

    pgg Laugh at me, will they? Moderator

    Joined:
    12.14.05
    Messages:
    7,451
    Location:
    Home Again
    Status:
    Attending Physician
    Navy SDN 7+ Year Member
    My understanding of the physics is that absorption atelectasis is impossible in the presence of PPV/PEEP, regardless of FiO2. And this makes intuitive sense: if there's sufficient gas pressure and airways aren't collapsing during the inspiratory phase, any gas (O2 or not) that's absorbed will be replaced.

    For spontaneously ventilating patients I always leave a bit of CPAP on or add a few cm of pressure support to help prevent atelectasis. But the issue here is more one of FRC and closing volume rather than gas mixture.

    Absorption atelectasis occurs when small airways close, distal areas don't have gas movement, and that gas gradually follows its concentration gradient into tissues, collapsing the alveoli. This can be hastened by denitrogenation but avoiding high FiO2 doesn't prevent it. You're better off optimizing your ventilation parameters to keep closing volume under FRC than worrying about the gas mixture - mostly this means providing adequate PEEP in ventilated patients, and not letting the spontaneous breathers suck unassisted through a straw for too long.

    I use higher FiO2s more often than not, the main exceptions being airway procedures where there's a higher risk of setting the patient on fire. I just don't see atelectasis that I can blame on the FiO2.

    One of the texts - don't remember if it was Barash or Miller, maybe M&M - dismissed absorption atelectasis outright as clinically insignificant. In any case, I don't think there's good cause to avoid higher FiO2s for fear of absorption atelectasis.
  32. aredoubleyou

    aredoubleyou Senior Member

    Joined:
    02.20.05
    Messages:
    616
    SDN 7+ Year Member
    Change in the compliance curve, the least depedent aveoli are preferentially ventilated now (unlike under spontaneous breathing where the more depedent aveoli are preferently ventelated)
  33. Licoricestick

    Licoricestick

    Joined:
    03.13.09
    Messages:
    289
    Location:
    Australia
    Status:
    Resident [Any Field]
    SDN 2+ Year Member
    If 100% O2 at 0.25ml/min is enough to supply the O2 needs of your patient - you might be anaesthetising in the morgue.
    Last edited: 12.10.09
  34. dhb

    dhb Member Lifetime Donor

    Joined:
    07.12.06
    Messages:
    2,592
    Status:
    Attending Physician
    SDN 7+ Year Member
    indeed , i meant 0.25L/min = 250 ml/min

    I'm still not down with the valve closing: when you switch the vent to automatic (controlled ventilation) mode aren't you bypassing the APL?
  35. somedumbDO

    somedumbDO

    Joined:
    09.18.06
    Messages:
    213
    SDN 7+ Year Member
    10 min??? you dont use much iso do you
  36. militarymd

    militarymd SDN Angel

    Joined:
    12.17.03
    Messages:
    5,883
    Status:
    Attending Physician
    SDN 10+ Year Member
    he is, after all, just a resident.

// Share //

Style: SDN Universal