Question about vent weaning

[waterbottle10]

I keep getting taught by people that you use pressure support for vent weaning. I dont really get it. Why not just lower the Peep, RR, Vt on A/C?

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[Ezekiel2517]

You don't need to use PS. But it helps in certain situations and patients. Just think about it, how do they extubate patients in the ICU?

 

[PainDrain]

PS allows the patient to initiate the breath and "exercises" them a little. It also helps to determine if they are breathing at 10bpm or 40bpm and whether they will be extubateable and taking adequate tidal volumes as you lower the support. AC will give a pre-determined volume at a set frequency and the patient may not "sync" with the vent, which aside from being uncomfortable for the patient may lead to other problems.

 

[G-Man82]

Are you talking about vent weaning in the OR for a patient under GA? Or about ICU ventilator weaning where we have patients who are essentially awake and triggering the ventilator?

Keep in mind, we don't use A/C in the OR. That's an ICU ventilator mode that can be either pressure or volume controlled. The RR on A/C is essentially a minmim or backup. The vent will assist by delivering a set pressure or volume at the minimum set RR, or if the patient is breathing (triggering), deliver said Vt or P with each triggered breath. If a patient is breathing at a rate of 18 and the RR set on the vent is 15, you can drop the RR to 4 or whatever you like, but the patient will get the 18 breaths he is triggering.

PSV is nice because it slowly shifts the work of breathing to the patient. It's nice in the OR because often you can set a backup RR, or add the mode into your control mode (Draeger Apollo), and slowly shift a patient to PSV and wean to SV/extubation at end of the case. You lower the RR on a controlled mode in the OR under GA because you want to build co2 and get the patient to breathe on their own. You can do this by lowering Vt too. Changing peep doesn't truly wean a patient because peep won't drive their own spontaneous respiration; it's more to maintain oxygenation.

Hope this helps. There are other parameters you can play with in either mode (inspiratory times, flow vs pressure triggers, changing the peak flow rate at which PSV cycles to exhalation, etc) if you really wanna be precise, but often that's unnecessary in the OR.

 

[fakin' the funk]

Most patients in the ICU who are getting "weaned" from the ventilator (and this depends very much institution to institution) go from volume A/C to a spontaneous breathing trial (SBT). Often this SBT is PSV mode, something like PEEP 5 PS 5 ("5 over 5"), but it can be CPAP or just "zero over zero" unsupported ventilation.

If they do OK on that, then they get extubated.

The virtue of using PSV or CPAP as a "bridge" to extubation is that it exercises the patient's diaphagm a little and more accurately simulates their extubated physiology than A/C. In A/C weaning, even if you lower their rate so that they are triggering extra breaths, all of those breaths are 100% machine work.

 

[pgg]

We generally aren't intubating patients in the OR for respiratory failure so in that context, the word "wean" is an overly dramatic way of saying "turn off the gas and don't give too much opiate and make sure there's no residual NM blockade" ... and the vent mode matters not one bit.

Are you talking about prolonged ventilation in ICU patients? That's a different world, but even so I wouldn't get all dogmatic about the right and wrong vent strategies to wean a patient. So long as you're withdrawing support in a an appropriately gradual manner and sensibly applying your extubation criteria before pulling the tube, arguing over PS vs AC vs turn it off and see how they fly on a T piece seems kind of silly.