Why do RT's love PRVC?

[VentdependenT]

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I had a dude hicupping on vent, AC was alarming constantly. I tinkered around for a while and finally ended up on pressure control. RT came in later as I was dropping fio2 and recommended prvc.

I said sure. vent didnt agree with pt and was going nuts changing flows. tidal volume still variable as dude sucking in and stacking with hiccups. Finally ended up back on PC. He was gorked so sedation not in equation.

Whats up with PRVC? You guys use it? Does it really keep the peaks down? Does it screw I:E's up badly and cause breath stacking? Why do RTs use it as solution to "dyssynchrony." I never use it, but then again ive never used bilevel or aprv either.

 

[Hernandez]

Solution in search of a problem. And every manufacture's version is slightly different. My philoshy is to **** or get off the pot.

Pro's: limits pressure
Con's: lose of mandatory MV, you never know what the I:E will be, it seems to cause more dyschrony (IMHO), RTs seem to think its some sort of safe mode they can don't have to monitor as closely in these pts who alarm constantly

Find the problem causing high airway pressures and fix that if you can, otherwise, stick with pure VACV or PACV

 

[Bostonredsox]

We used PRVC at one of the MICUs I rotated through in med school. We have one here at my shop, have never seen it used. Makes sense to me, VC on autopilot self adjusting for elevated PAPs.....I doubt it's ever been shown to affect mortality or weaning, vent days, etc.

 

[jdh71]

Well, to be fair it's probably the more comfortable of the various "volume control" modes. All things being equal.

Though it would definitely be the wrong mode for the hiccuping patient.

 

[sluggs]

It still boggles my mind that anyone uses volume control regularly. PC gives much more exquisite control of plats.

 

[KLPM]

Forgive my ignorance but what exactly is a respiratory therapist? I have never heard of this role in my country (could be a function of my ignorance). What do they do exactly?

 

[dotcb]

some questions are best asked to Dr. Google:

http://en.wikipedia.org/wiki/Respiratory_therapy

 

[Hernandez]

It still boggles my mind that anyone uses volume control regularly. PC gives much more exquisite control of plats.

Nothing wrong with Vacv for the vast majority of patients, especially if your hospital in their infinite wisdom doesn't allocate enough RTs for your Icu. Pacv and changing compliances dont mix unless someone is watching. Also no one has compared vacv to pacv for ARDS that I'm aware. And I doubt you will see a true head to head as there is some data to suggest its just as much the large tidal volume as it is the pressure that causes issues.

 

[jdh71]

It still boggles my mind that anyone uses volume control regularly. PC gives much more exquisite control of plats.

Lots of ways to skin a cat. You can also dial in volumes that give you the pressure you want right?. Which is what PVRC is trying to do.

I set my vents up to patient comfort unless the current respiratory failure process dictates I be more strict with my settings.

I like "pressure control". I actually think in many ways its a much more intuitive approach to the ventilator but the entire industry standard starting point currently is the volume control modes so for the sake often of not having to deal with bull**** from people who dont get it I tend to start there too.

 

[VentdependenT]

Nothing wrong with Vacv for the vast majority of patients, especially if your hospital in their infinite wisdom doesn't allocate enough RTs for your Icu. Pacv and changing compliances dont mix unless someone is watching. Also no one has compared vacv to pacv for ARDS that I'm aware. And I doubt you will see a true head to head as there is some data to suggest its just as much the large tidal volume as it is the pressure that causes issues.

PACV should be fine but it does require more than the "Set it and Forget it until tomorrow" mentality.

I do find that pts who are not comfortable on VACV tend to be more comfy on pressure control. But I rarely see anyone use it. Our institution treats every firggen pt on a vent with ards Ttidal Volumes and pts have severe air hunger.

 

[Hernandez]

Lots of ways to skin a cat. You can also dial in volumes that give you the pressure you want right?. Which is what PVRC is trying to do.

I set my vents up to patient comfort unless the current respiratory failure process dictates I be more strict with my settings.

I like "pressure control". I actually think in many ways its a much more intuitive approach to the ventilator but the entire industry standard starting point currently is the volume control modes so for the sake often of not having to deal with bull**** from people who dont get it I tend to start there too.

👍 I have flow wars with the RTs, most of them think 40L/min is appropriate, I titrate it and volume to what appears to be pt comfort. Hell, I'll even go wild and on pts like bad DKA or someone with healthy lungs and respiratory drive that want to breath down CO2 for a metabolic acidosis, I'll even let them ride on PSV/CPAP and let them control the minute ventilation. But that doesn't fly for one of my attendings who'd put everyone on 4-6mL/kg.....COPD pts don't do well with that low TV

PACV should be fine but it does require more than the "Set it and Forget it until tomorrow" mentality.

I do find that pts who are not comfortable on VACV tend to be more comfy on pressure control. But I rarely see anyone use it. Our institution treats every firggen pt on a vent with ards Ttidal Volumes and pts have severe air hunger.

Some institutions use nothing but PACV, I'm a big fan of it. But at my fellowship, they treated it as mythical and as a salvage mode due to the inherent improved oxygenation. If I had someone on PACV who wasn't sick, the nurses would look at me like I'm crazy due to the culture

To me, I'd think PACV would be more comfortable by allowing a little more pt control that's more in line with how we physiologically control TV anyways

 

[Stitch]

During residency my attendings used mainly PC and that's what I got comfortable with, but here they use a ton of PRVC. I like it and it works well generally. No problems with breath stacking (I'll use low rates and PC for asthmatics) or I:E issues. It's just convenient when compliance may be changing.

I've never used volume control to tell the truth. It may just be a peds thing though. We've also starting using aprv a lot lately, and in the right patient it works quite well.

 

[Hernandez]

I much prefer APRV to VC+

 

[VentdependenT]

I much prefer APRV to VC+

For what?

I have ZERO experience with this mode

 

[Hernandez]

For what?

I have ZERO experience with this mode

Dyschrony.... for pts who have a lower required minute ventilation.

I look at APRV as two modes, bilevel with a normal I:E, or APRV with prolonged I:E for treatment in ARDS. easiest way to look at it as underlying PACV that also allows PSV on top of the PACV.

 

[sluggs]

Nothing wrong with Vacv for the vast majority of patients, especially if your hospital in their infinite wisdom doesn't allocate enough RTs for your Icu. Pacv and changing compliances dont mix unless someone is watching. Also no one has compared vacv to pacv for ARDS that I'm aware. And I doubt you will see a true head to head as there is some data to suggest its just as much the large tidal volume as it is the pressure that causes issues.

Can you point me to real data showing that "large tidal volume" causes issues if you are using pressure control ventilation and controlling plats less than 25? I think the real culprit in ARDS has been volume AC and the high plats associated with high-volume volume AC. Animal models have demonstrated that the culprit in ARDS is high trans-pulmonary pressure gradient. I have been reading about this a lot, and am still trying to get to the bottom of it, but thusfar, I think that using pressure control, or even Psupp in "breathers" is superior to volume AC, which can still produce high plats at 6 cc/kg PBW.

 

[sluggs]

I much prefer APRV to VC+

I also agree that APRV is lung-protective, and is a great mode once you understand it!

 

[Hernandez]

Can you point me to real data showing that "large tidal volume" causes issues if you are using pressure control ventilation and controlling plats less than 25? I think the real culprit in ARDS has been volume AC and the high plats associated with high-volume volume AC. Animal models have demonstrated that the culprit in ARDS is high trans-pulmonary pressure gradient. I have been reading about this a lot, and am still trying to get to the bottom of it, but thusfar, I think that using pressure control, or even Psupp in "breathers" is superior to volume AC, which can still produce high plats at 6 cc/kg PBW.

I you look at the ARMA data, even in pts with plat <30cm, the lower tidal loumge groups had better mortality outcomes. If you listen to Niel Mcyntire give a talk, he goes into it. Also chest had a point-counter point ~a year ago talking about PACV vs VACV that went into data to date. S even when I use PACV for ARDS, I titrate the pressure to a tidal volume or ~6mL/kg

 

[sluggs]

Again, though, all of this data is using Volume AC?

 

[Hernandez]

Again, though, all of this data is using Volume AC?

The only data I'm aware of that used PACV was the recent HFOV trial....and they did the same thing. Titrate the pressure to a TV ~6mL/kg, and their outcomes for control rm was similar to ARMA.

Lack of data does not prove your hypothesis.

 

[Bostonredsox]

I much prefer APRV to VC+

we don't have APRV vents so I cant do the high peep low peep stuff but I have done PC-IRV on a few severe refractory hypoxemics and I think that is essentially APRV is it not?

As for VACV vs PACV....I use both. The 2 actual pulm/cc docs we have use both. the one educated cc hospitalist we have uses both. if any point a general hospitalist is in here or for new night admits from gen hospitalist...they exclusively use VACV as none of them have any training on PACV i've concluded. every single pt they admit is on VACV 14, PEEP 5, TV 500 and FiO2 varies based on if they coded or not. doesn't matter if its severe metabolic acidemia with pH 7.0....rate is still 14. scary sometimes. I use PACV frequently on the bad COPDrs with poor compliance, espec the obese ones. also use it on the drunks a lot. I think its smoother ventilation. However I agree with you guys, cant set it and leave it. If your compliance issues are dynamic and not fixed, a sudden increase in compliance can skyrocket your TVs to an unsafe volume. That's why Im scared to use it in ARDS here despite high platueu's being demonstrated as being just as dangerous as big TVs in the ARDSnet trials. If I had 24/7 fellows/attending's or even senior residents who could trouble shoot the vent, and a higher # of RTs to keep an eye on things id use it more.

 

[idiot07]

The kicker with APRV is the patient can spontaneously breath on top of the peep high/low pattern, a la PSV with a changing peep, which is supposed to make it comfortable, and you can get the oxygenation benefits of PC-IRV without having to paralyze the patient. In my mind, the lack of paralytics is the chief benefit. I've used it some and it works seems to work awesome half the time and the other half I can't get the patient and vent to synch well. We have drager vents with bilevel, which we use to simulate aprv, instead of real APRV, not sure which vents actually have this, so I'm not sure if this is the problem or what. The other issue for me is that RT's and cross covering residents may not be real familiar with it which led to the patient getting paralyzed and placed on pcirv if there's a problem when I wasn't on call. I kind of gave up on it, but some people swear by it. The RT's like VC+/PRVC cause they don't have to track the tidal volume as closely as they do with pure PCV. I think it's nice if the patients getting better and lung compilance is changing, but they're pressures aren't quite ready for VC or they're not comfortable on VC. I think the better way to think of it rather than VC adjusting for pressure, is PC with the vent adjusting pressure to obtain the TV you want.

 

[souljah1]

We use a ton of AC/VC and are able to adapt it to the patient pretty easily. For patients with severe ARDS we'll occasionally do AC/PC with inverse ratio. We rarely use APRV. I occasionally use AC/PC for patients who, for whatever reason, appear more comfortable than AC/VC. Given that compliance is constant, it doesn't really matter whether your hold volume or pressure constant. People who hold strong feelings about PC versus VC simply don't understand that it doesn't matter all that much.

PRVC is not often used for anyone in the throws of acute illness. Because it adapts flow you often get a lot of variation with tidal volumes. Not good at all for ARDS.

 

[BigRedBeta]

"Grew up" in my residency (peds) using PRVC exclusively (and it was all AC, no SIMV ever, weaned to volume support and Automode on the Servo I vents), and now I'm in a fellowship that starts with PC/PS without fail...

Have to say that I love PRVC conceptually and if given the option (with nurses/RT's/residents who understood it) would choose it as my starting place every time. In practice, however, it's not always ideal. But I've noticed a significant difference between different brands of vents - I believe it works significantly better on the Servo I from Maquet/Siemens than on the Aveas my current unit uses. The difference as I can tell is that the Servos seem to average over a larger sample size of breaths while the Avea seems to change literally breath to breath - which is only exacerbated by the higher RR's in pediatric patients.

I've had some attendings posit that in the patient in distress, that as they initiate larger efforts, they generate more negative inspiratory pressure, the machine will deliver less support making the problem worse, while one of my mentors in residency had unpublished data suggesting that there was far less dyssynchrony in PRVC/AC than any other vent mode except for PSV.

In the end, I really think there's a hundred ways to skin a cat when it comes to vents. Perhaps it's because in peds we're forced to operate without much evidence, I don't really think mode matters much, so long as you're matching your patient's needs. While varying strategies of ventilation may be better (low tidal volumes, low PIP's, etc), I doubt anyone will ever find a particular mode superior as it relates to big outcomes like mortality/vent days/ICU days/etc., any superiority will come for things far down the list like synchrony and sleep.

 

[redy]

We use a ton of AC/VC and are able to adapt it to the patient pretty easily. For patients with severe ARDS we'll occasionally do AC/PC with inverse ratio. We rarely use APRV. I occasionally use AC/PC for patients who, for whatever reason, appear more comfortable than AC/VC. Given that compliance is constant, it doesn't really matter whether your hold volume or pressure constant. People who hold strong feelings about PC versus VC simply don't understand that it doesn't matter all that much.

PRVC is not often used for anyone in the throws of acute illness. Because it adapts flow you often get a lot of variation with tidal volumes. Not good at all for ARDS.

I am not sure I follow. The tidal volumes are even more variable in pressure control obviously. So why would you use PC over PRVC?