ICU vent vs. Anesthesia Vent

[RxBoy]

Some questions about vents...


With VC using my anesthesia vent, I have no way to control the actual inspiratory flow (not FGF) however I am able to adjust the I:E ratio. Is this because my machine just predicts the flow needed (dummy proof)?

For example if I set 600 mL for RR of 10 at I:E of 1:1, does that mean the vent just knows to deliver 600 mL in 3 sec (inspiratory flow at 200 mL/s).

Next question is even if I turn inspiratory pause completely off, my machine is still able to give me both peak and plateau pressures and looking at the Pressure/time tracing I can still see a peak followed by a quick drop to plateau then the expiratory drop. Does this mean the machine forces a quick inspiratory pause with each TV just so it can calculate the Plateau?

I know with our ICU vents with VC, the only way to adjust I:E ratios, the flows have to be adjusted (which then displays the I:E ratio). It also never displays a plateau pressure unless you manually force an inspiratory pause. It does however display the Pressure Mean which is a nice number to know for oxidation reasons, while our anesthesia vent doesn't.

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[PMPMD]

Some questions about vents...


With VC using my anesthesia vent, I have no way to control the actual inspiratory flow (not FGF) however I am able to adjust the I:E ratio. Is this because my machine just predicts the flow needed (dummy proof)?

For example if I set 600 mL for RR of 10 at I:E of 1:1, does that mean the vent just knows to deliver 600 mL in 3 sec (inspiratory flow at 200 mL/s).

Next question is even if I turn inspiratory pause completely off, my machine is still able to give me both peak and plateau pressures and looking at the Pressure/time tracing I can still see a peak followed by a quick drop to plateau then the expiratory drop. Does this mean the machine forces a quick inspiratory pause with each TV just so it can calculate the Plateau?

I know with our ICU vents with VC, the only way to adjust I:E ratios, the flows have to be adjusted (which then displays the I:E ratio). It also never displays a plateau pressure unless you manually force an inspiratory pause. It does however display the Pressure Mean which is a nice number to know for oxidation reasons, while our anesthesia vent doesn't.

With your second question about Pplat, at least with the Dragers I trained on, there was a small period of plateau on the volume waveform on VC.

With your first question, I believe that the machines do have that calculation built in. I don't think there's that big of a market for ICU-type vent settings in an anesthesia vent.

 

[countingdays]

With your second question about Pplat, at least with the Dragers I trained on, there was a small period of plateau on the volume waveform on VC.

With your first question, I believe that the machines do have that calculation built in. I don't think there's that big of a market for ICU-type vent settings in an anesthesia vent.

Older machines I've worked with had a flow dial that you'd have to adjust. It was more a pain in the ass than a useful feature.

 

[PMPMD]

Older machines I've worked with had a flow dial that you'd have to adjust. It was more a pain in the ass than a useful feature.

Oh yeah, I think the Narkomeds had it.

 

[rocuronium]

Some questions about vents...


For example if I set 600 mL for RR of 10 at I:E of 1:1, does that mean the vent just knows to deliver 600 mL in 3 sec (inspiratory flow at 200 mL/s).

Another thing to consider is the flow waveform. Some ventilators allow you to set it, some don't. Either way, the ventilator will calculate the flow based on the tidal volume set and the inspiratory time that is either directly or indirectly set.

Do you guys ventilate with pure VC in the ICU setting often?

 

[PMPMD]

Another thing to consider is the flow waveform. Some ventilators allow you to set it, some don't. Either way, the ventilator will calculate the flow based on the tidal volume set and the inspiratory time that is either directly or indirectly set.

Do you guys ventilate with pure VC in the ICU setting often?

It's institutional. I've trained in units that were all volume cycled, and ones that were all pressure cycled. As long as you know what you're doing. I'm not aware of any outcome data for PC vs VC as long as the VT and Pplat are kept constant.

 

[RxBoy]

Older machines I've worked with had a flow dial that you'd have to adjust. It was more a pain in the ass than a useful feature.

Interesting... It is def much easier to control with preset I:E ... I was just curious and now the "flow dependent" concept of VC makes so much more sense.

Do you guys ventilate with pure VC in the ICU setting often?

Exactly what PMPMD said above. But if you are referring to "pure VC" as in no AC, then no its extremely uncommon in the ICU setting. In anesthesia we routinely use pure VC or PC because the patient is rendered unconscious and paralyzed with an inability to initiate a breathe.

 

[RxBoy]

Some questions about vents...
Next question is even if I turn inspiratory pause completely off, my machine is still able to give me both peak and plateau pressures and looking at the Pressure/time tracing I can still see a peak followed by a quick drop to plateau then the expiratory drop. Does this mean the machine forces a quick inspiratory pause with each TV just so it can calculate the Plateau?

For those very VERY few that actually care, I asked a really smart RT guy at our hospital and he said that its because anesthesia machines always have a FGF inlet during the inspiratory cycle (the FGF flow dial we set). He said this stacks on the delivered TV and our machines compensate for the FGF by decreasing inspiratory flow to maintain the desired TV. But this FGF also allows the peak pressure to decrease to plateau at the very end of inspiratory cyce whereas the ICU vent completely ceases airflow. After flipping through Dorch, I found a diagram representing this:

I know its real nerdy and not clinically useful, but I thought it was pretty interesting.

 

[PMPMD]

For those very VERY few that actually care, I asked a really smart RT guy at our hospital and he said that its because anesthesia machines always have a FGF inlet during the inspiratory cycle (the FGF flow dial we set). He said this stacks on the delivered TV and our machines compensate for the FGF by decreasing inspiratory flow to maintain the desired TV. But this FGF also allows the peak pressure to decrease to plateau at the very end of inspiratory cyce whereas the ICU vent completely ceases airflow. After flipping through Dorch, I found a diagram representing this:

I know its real nerdy and not clinically useful, but I thought it was pretty interesting.

Nice, thanks for posting that.

 

[rocuronium]

Exactly what PMPMD said above. But if you are referring to "pure VC" as in no AC, then no its extremely uncommon in the ICU setting. In anesthesia we routinely use pure VC or PC because the patient is rendered unconscious and paralyzed with an inability to initiate a breathe.

What I mean by pure VC is volume assist control. People in most places where I have worked have the tendency to call volume targetted dual modes (e.g. PRVC, Autoflow, etc) volume control, which can be confusing. They also tend to use those modes almost exclusively. The benefits are a decelerating flow waveform with "unlimited" flow on demand, and not having to fiddle with flow settings. There are, of course, a few drawbacks. I've never used VC on a non-paralyzed patient, and I think it would be uncomfortable for most ICU patients. I understand its use in the OR.

I'm always interested to hear how other people ventilate their patients.

 

[Hernandez]

I've never used VC on a non-paralyzed patient, and I think it would be uncomfortable for most ICU patients. I understand its use in the OR.

VC is not that difficult to adjust in an ICU pt, at least on the PB-840, in the models you can adjust flow, just make sure you're giving enough and the pt isn't sucking down on the tube trying to breath over what you're delivering. typically 1L/sec (or 60L/min) is where I start, I rarely go less than that even though our RTs sit there and fiddle it till they get the I:E right at 1:2. of course if you can't adjust flow like in the iServos, you not have the I:E to adjust.

personally, Im not a fan of pressure-regulated volume control modes. my philosophy is to **** or get off the toilet. if thre's an issue with pressure, I need to know why and figure it out

 

[rocuronium]

VC is not that difficult to adjust in an ICU pt, at least on the PB-840

I agree. It's nice that you can lock in either a Ti or I:E when making changes in VC.

Have you experimented with PAV on the 840 at all?

 

[Hernandez]

I agree. It's nice that you can lock in either a Ti or I:E when making changes in VC.

Have you experimented with PAV on the 840 at all?

Yeah, but the cases we have long term wean plans on require really high pressures on PAV (30-40) of PSV from PAV. The peoplewho take afewdaya to wean don't seem to wean any faster on PAV. At that point you still have to keep an watch on WOB and if the machine is I'm the green zone so it doesn't allow for less RTcare. I personally preferably aggressive RT with PSV/CPAP wean or SIMV/PSV for the really really hard PTs to wean