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vent weaning, or how i learned to stop worrying and love the code blue

Discussion in 'Other Subspecialties' started by tum, Apr 10, 2007.

  1. tum

    tum don't call it a comeback
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    i think this has been discussed before, but i've tried searching through the forums for awhile and couldn't find the thread. quick question about vents for any of you battle weary pgy-2-8s.

    when you're weaning someone off SIPS do you go down on RR first or do you drop the PSV? this is assuming the RSBI is ok. i always thought you backed off on the resps till you had just pressure support, but then i heard it backwards today from someone who i thought was pretty with it.

    any ideas?
     
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  3. Eidolon6

    Eidolon6 Senior Member
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    Although it seemed intuitive that to "wean" someone from the ventilator, you should use an SIMV mode, backing off on the manditory breaths as you go....this has been debunked by two large randomized controlled trials that are about 12 years old (see Esteban in NEJM ~1994). These trials showed that the SIMV habit of weaning back the manditory rate actually increased time on the ventilator and was inferior to spontaneous breathing trials.

    What we know is that daily spontaneous breathing trials (going from assisted ventilation to either low PS, CPAP or T piece, take your pick) are the best way of "weaning" the patient from the ventilator sufficed that the patient is on minimal additional support from the ventilator (PEEP<8, FiO2<50%). A "trial" consists of 30 minutes on one of the three modes above. So long as the patient's acute problem is resolving, doesn't have a secretion or ongoing neurologic/airway protection issue and doesn't marked increase RR, decrease Vt or become hypoxemic (you can also encorporate the RSBI)...they can be extubated.

    For weaning patients on long term mechanical ventilation....pressure support intervals can be used daily....but SIMV is contraindicated for these people (again...it increases work of breathing)

    SIMV is an inferior mode of ventilation because it causes increased WOB and ventilator dysynchrony and Assist control (volume or pressure cycled) are superior. Sadly, the use of SIMV is still around, especially in surgical units and nonacademic ICUs where practice is not so up to date.
     
  4. tum

    tum don't call it a comeback
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    Sorry for my ignorance--I did come across that data in my reading, and I was unsure how to resolve it with what I saw at the ICU I was rotating at. So to make sure I understood you--in most situations, you would rather keep someone ventilated on AC (as opposed to SIPS), then to wean them you would go with intermittent spontaneous breathing trials with T-piece/CPAP?
     
  5. Eidolon6

    Eidolon6 Senior Member
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    No need to apologize. My practice is to use spontaneous breathing trials to assess for extubation readiness. I generally use assist control for full ventilator support. I do use pressure support ventilation in those patients who can tolerate it but did not pass their SBT however I am mindful that these patients are doing work when on pressure support and can become exhausted with supervision.
     
  6. tum

    tum don't call it a comeback
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    i came across something that said with pressure control ventilation you should try to wean with spontaneous breathing trials + pressure support, while with volume-control you should lean more towards t-tubes.

    this makes instinctive sense, but i was unaware of any clinical trials that showed a benefit to the different extubation pathways.

    anyone want to throw up their pennies?
     
  7. gutonc

    gutonc No Meat, No Treat
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    I think there are 2 main reasons that T-tube trials are less common than SBT these days. 1 is that you (or RT more likely) has to go hunt down a T-piece where for an SBT they just push a couple of buttons on the vent. The other main reason is that w/ a T-pice you can't monitor how much air they're pushing on their own since you take the vent (and its measuring abilities) out of the circuit so you generally have to use other markers (BP, HR, Sats, ABGs) than the "Tobin" score to determine who gets to lose the straw. On my last unit month a couple of months ago we were talking about this as well and a quick lit search didn't bring up any good data on whether T-piece vs. SBT was better.
     
  8. gwen

    gwen Senior Member
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    i'm sorry, but its LIBERATION, not weaning. :smuggrin:
    just kidding, one of our ICU attendings was really picky about our English.
     
  9. 2ndyear

    2ndyear Senior Member
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    This is absolutely true. As an anesthesia resident, we rotate through a SICU where SIMV is 'the' mode. Standard protocol is to decrease the breaths all the way to 4, then switch to PSV and go from there. Drove me nuts. Here's what I did to overcome resistance from the RT's and RN's (who really run the show as you all can attest to): Add pressure support to the spontaneous breaths on SIMV and pressure limit the SIMV mode. Now you have pressure control. If I recall, the Esteban study was done with basic SIMV, ie: spontaneous breaths have PEEP and that's it. Then I would physically bring the RT to the bedside and regardless of the set rate, have them switch to PSV if the patient was getting close to liberation, that way we were both standing by 'just in case'.

    PSV trials? Nope. Sedation holidays? In protocol only. Patients routinely under general anesthesia...every single day. And this is an academic center.
     
  10. DropkickMurphy

    DropkickMurphy Membership Revoked
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    You can.....you just have to use a respirometer, which can be a pain in the ass.

    Show me a place where the residents or students do things like that and I will apply there as an RT. I will also bring said resident or student coffee at the beginning of my shift.

    There is a serious lack of literature (at least that stands up to scrutiny) on which has better utility (T-piece vs SBT), but many of the docs I've worked with seem to prefer a CPAP trial over the use of a T-piece because of the lack of the need to break the circuit and expose the patient to a (real or imagined) "increased risk" of VAP. To my knowledge I don't believe there is any research on this notion in the literature. Personally, if given my choice, I would do something akin to what 2ndyear described, although I hate SIMV with a passion.
     

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