# Vent Modes



## cointosser13 (Feb 15, 2017)

This more pertains to critical care paramedicine, but I was wondering: how do you remember what each vent mode (A/C PRVC SIMV etc) does when ventilating a patient? Any tricks (or charts) to remembering what each one does?


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## Handsome Robb (Feb 15, 2017)

@VentMonkey

I'll be back, I just finished a 48 and I'm beat so I'm going to nap. 


Sent from my iPhone using Tapatalk


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## VentMonkey (Feb 15, 2017)

cointosser13 said:


> This more pertains to critical care paramedicine, but I was wondering: how do you remember what each vent mode (A/C PRVC SIMV etc) does when ventilating a patient? Any tricks (or charts) to remembering what each one does?


There are apps that I carry, and peruse from time to time on my phone (basics of mechanical ventilation is the one I review the most from time to time, and it has the modes you've listed in your post). Just know with ventilator management there is no one-size fits all approach.

I also recommend giving Eric Bauer's book on prehospital ventilator management a look, as well as his, and Weingart's podcasts. They have some stuff that is unconventional though, and requires quite a bit of experience (many of it far beyond even my comfort zone, and level), and may not be well received by the masses at your particular program. YouTube, and Google also did wonders---and still do---when I first began delving into vent management.

If you have any RRT/ RCP colleagues, pick their brains; if you run into any pulmonologists pick theirs as well. Understand everything there is about the respiratory system to the best of your ability from basic adjuncts (e.g., never not transport your vented patients without a BVM/ mask at the ready, and easily accessible to you), get familiar with ABG's, and different formulas that may benefit certain patient types (e.g., Winter's Formula for a critically ill intubated, and ventilated metabolically acidotic patient), and get familiar with the ARDS net group, their literature, and publications.

Also, consider the type of ventilator you use, and get to know it back, and forth, play with it, do routine vent checks til you're comfortable with the basic set ups and modes. As far as when to use to different modes/ what they do, again, you will hear 10 different people cite 10 different uses. If your ventilator has PRVC, then you're well ahead of most of the soon-to-be phased out prehospital vents as this is a combination mode which as the name implies offers volume-control ventilation while calculating the patients initiated pressure limits so to speak. You may also see CMV-assist listed as AC, CMV alone is a pretty obsolete mode that has very limited use at least at my program. I hope this helps you some.


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## VFlutter (Feb 15, 2017)

https://www.openanesthesia.org/modes_of_mechanical_ventilation/

No sure if there are many tricks to learning vents other than just remembering the information and the physiology behind it.


Maybe something like this would help.


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## VentMonkey (Feb 15, 2017)

...aaand one more link added to my "work" folder, thanks @Chase.


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## RocKetamine (Feb 15, 2017)

I'm not really sure if there are any tricks to learning the modes, it's probably just one of those things that need memorization. There are tons of YouTube videos, power points, podcasts, etc... to answer pretty much any question you have. 

I'd also suggest buying Eric Bauer's book on ventilator management. That said, I don't agree with his SIMV only strategy for all patients. Ventilator management can vary so much from patient to patient that it's dangerous to teach modes as a "one size fits all" approach, like VentMonkey said above.


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## VentMonkey (Feb 15, 2017)

RocKetamine said:


> That said, I don't agree with his SIMV only strategy for all patients.


I think it's a fail safe option for providers lacking the dual encompassing PRVC mode, however, I think you're right in that it should not be used on every patient given the likelihood of damage that one can inflict with the incorrect mode of an acutely ill patient that may require more ventilator dependency; he's a big proponent of patient comfort, and what I would presume to be less ventilator dependency in an effort to encourage weaning sooner rather than later, which I don't necessarily disagree with, but each mode is certainly circumstantial to the patient at hand. 

I sure do find ASV an interesting mode for most patients, but again, it is not an _all _encompassing ventilatory mode, just one intended to get us from the scene post induction/ intubation to the ED; it seems sufficient as more often than not the patients we're picking up from scenes, and placing on our vent are most likely not going to experience any acute deleterious effects of this mode, or any of the ones we use for them (PRVC being the other go-to) in a routine 15-30 minute flight to our regional ED's.


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## StCEMT (Feb 15, 2017)

VentMonkey said:


> (e.g., never not transport your vented patients without a BVM/ mask at the ready, and easily accessible to you),



I learned the importance of this the other week. I had a BVM, I keep a mini airway bag stocked on the stretcher all the time anyway. However, we ended up needing to pull out the BVM for quite a while. Definitely an important reminder for me. Otherwise, I am going back to lurking, because I am interested in seeing what pops up here.


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## VentMonkey (Feb 15, 2017)

StCEMT said:


> I learned the importance of this the other week. I had a BVM, I keep a mini airway bag stocked on the stretcher all the time anyway. However, we ended up needing to pull out the BVM for quite a while. Definitely an important reminder for me. Otherwise, I am going back to lurking, because I am interested in seeing what pops up here.


I like threading the oxygen tubing through the mask itself and setting it on their lap, and/ or next to my person in flight; it serves as a good visual reminder for me. We do have the BVM behind the paramedic seat, but it can be a PITA for me to reach, so I try and leave the BVM where myself, or partner(s) can grab it in a pinch. 

If my medic bag has to go in our aft compartment for storage my partner or I will pull out the VL as well should the tube become dislodged or what have you in-flight; this is standard for all of us. We have a spare intubation kit in the paramedic door than can be utilized as well, but the VL is only in the medic (first-in) bag so we have to grab it before we're in-flight.


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## TXmed (Feb 15, 2017)

While its always a fun debate, really the strategy between A/C and SIMV is based on preference and models of ventilators.

ASV i have no experience with but i hear great things about.

The biggest thing i tell people eager to learn about transport vents, is focus your studying on how to use volume vs pressure modes.

I generally use pressure but when i have the sickest of the sick i will switch to volume


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## Brandon O (Feb 15, 2017)

Discussion of basic modes here that may be helpful.


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## VentMonkey (Feb 16, 2017)

Brandon O said:


> Discussion of basic modes here that may be helpful.


Thanks for the link. OP, this is an excellent starting point; also added to my work folder on my phone.


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## STXmedic (Feb 16, 2017)

Brandon O said:


> Discussion of basic modes here that may be helpful.


New site? Very nice


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## Brandon O (Feb 16, 2017)

STXmedic said:


> New site? Very nice



Yep!


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## E tank (Feb 17, 2017)

Maximizing oxygenation/ventilation while minimizing volu/barotrauma is the simple goal, but getting out into the deep weeds isn't that hard sometimes. 

If I was only allowed one way to give mechanical ventilation, It would be pressure control (with peep, of course), just because I can give more volume for a given pressure and the patient can over breath the vent without too much difficulty.  If it's not objectively clear how to ventilate, I'd default to this and be very comfortable defending it.


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## Brandon O (Feb 18, 2017)

E tank said:


> just because I can give more volume for a given pressure and the patient can over breath the vent without too much difficulty.



Eh... eh? Not sure I understand the argument for either of these points.


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## E tank (Feb 18, 2017)

Brandon O said:


> Eh... eh? Not sure I understand the argument for either of these points.


Well, what specifically is the question?


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## Brandon O (Feb 18, 2017)

E tank said:


> Well, what specifically is the question?



In what respect does pressure control allow you to give more volume for a given pressure or make it easier to overbreathe?


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## E tank (Feb 18, 2017)

Brandon O said:


> In what respect does pressure control allow you to give more volume for a given pressure or make it easier to overbreathe?



Compared to VCV,  the decelerating flow pattern in PCV allows for the earlier dissipation of flow resistance which results in lower peak pressures for the same volume. This has all kinds of consequences, not the least of which is lower intrathoracic pressure, better venous return, and less intrapulmonary shunting. 

As to the second point, it depends on your ventilator, but when the machine sees the set pressure on bucking, it stops cycling a breath, whereas in VCV (not SIMV) it will continue to attempt to give the set volume until it does. I realize that some ventilators are more sophisticated than others and the ones I use are more forgiving of a breathing/bucking patient. Your results may vary. 

Note that in my post I said that if I were allowed only one mode of ventilation, I'd choose PC. I'm not in any way suggesting that other modes have no utility. I just reduced the conversation to that for the sake of simplicity for folks that have not had a lot of experience with mechanical ventilation.


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## Brandon O (Feb 18, 2017)

E tank said:


> Compared to VCV,  the decelerating flow pattern in PCV allows for the earlier dissipation of flow resistance which results in lower peak pressures for the same volume. This has all kinds of consequences, not the least of which is lower intrathoracic pressure, better venous return, and less intrapulmonary shunting.
> 
> As to the second point, it depends on your ventilator, but when the machine sees the set pressure on bucking, it stops cycling a breath, whereas in VCV (not SIMV) it will continue to attempt to give the set volume until it does. I realize that some ventilators are more sophisticated than others and the ones I use are more forgiving of a breathing/bucking patient. Your results may vary.



I think it's important to distinguish peak versus plateau pressure.

Most of what you're describing involves higher PEAK pressures. As I'm sure you recognize, the peak pressure (the driving pressure, measured and generated at the ventilator) is produced by a combination of two forces: the resistive pressure and the plateau pressure. The former is purely a dynamic phenomenon created by the resistance of the circuit, ET tube, and large airways (much like blowing through a straw). It is not transmitted or felt in the lung parenchyma, i.e. the alveoli. The latter is reflected by the plateau pressure, usually measured by an end-expiratory hold (although if PCV is configured to allow the flow to fully return to zero by the end of the breath, peak will equal plateau in that case).

Reducing peak flow has very little consequence. It is not lung-protective, because it is not felt by the alveoli, which is the portion of the lung that experiences injury. It probably has no impact on hemodynamics, since the large airways are not very compliant and transmit little pressure. As for plateau pressure, it is largely a consequence of volume, not of flow patterns. I recognize there is an argument that PCV can produce somewhat better recruitment, but this is mostly due to the fact that it is time-cycled, allowing essentially a breath-hold at full pressure, whereas in VCV the breath ends when the full volume is reached. (You can probably adjust VCV flow and use a decelerating-ramp waveform to get close to this if desired.)

If a patient is bucking, peak pressure may be increased, as will plateau. However, the thoracic pressure is equally increased (that's how they're transmitting pressure to the airway), so the transpulmonary gradient is NOT any greater. This is why nobody gets a pneumothorax from playing a trumpet or pooping or lifting weights, even though in that case airway pressures (against a closed glottis) may be tremendous. Pressure is high on both sides of the alveolar membrane.

I think PCV can be more comfortable in some patients due to the variable flow. I doubt there is ever a difference in outcome.


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## Carlos Danger (Feb 18, 2017)

As far as I know, no ventilation specific ventilation strategy is superior to any other in terms of outcomes.

E tank is right about tidal volumes. Put a patient on VCV at any given volume. Then switch them to PCV with the IP set at whatever the peak pressure was being generated by the first mode. You will almost always see a significantly increased tidal volume.


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## VentMonkey (Feb 18, 2017)

Remi said:


> As far as I know, no ventilation specific ventilation strategy is superior to any other in terms of outcomes.


This is turning into a good thread. To kind of bring it back to a novice ventilator management perspective though, this isn't to say that you cannot cause harm to your patients with poor vent management, specifically with long transport times in the out of hospital environment.


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## E tank (Feb 18, 2017)

In PCV, PIP=Pplat. 

 Like I said, my purpose wasn't to engage in a "less filling, tastes great" debate on minutiae. It was to de-clutter some of the confusion that the less experienced bring to the table when mechanically ventilating a patient. 

It's evident that different patients benefit from different modes of ventilation, both hemodyamically and with regard to gas exchange,  PCV being one. The literature is there for the mining, for what it's worth. 

As far as "bucking" goes, if the issue were just isolated to the intrapulmonary/thoracic pressures, there would less of an issue. But it's not. It raises ICP, MAP, and the HR as well. Healthy patient? Who cares? But I don't think that's what we're talking about.


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## Brandon O (Feb 18, 2017)

Remi said:


> As far as I know, no ventilation specific ventilation strategy is superior to any other in terms of outcomes.
> 
> E tank is right about tidal volumes. Put a patient on VCV at any given volume. Then switch them to PCV with the IP set at whatever the peak pressure was being generated by the first mode. You will almost always see a significantly increased tidal volume.



1. This is not magic. The PCV is probably just ending up with a longer I time.

2. This is not good. Set tidal volume based on what's lung protective and what's needed for ventilation. Bigger is worse, not better.

3. Ignore peak pressures. Plateau is what's relevant to most of our interests.


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## E tank (Feb 18, 2017)

1. So what? The volume is delivered at a lower pressure and that is done without adjusting anything else and it's "protective"

2. What's not good? Delivering more tidal volume at a lower pressure?

3. For all practical purposes, PIP = Pplat when giving PCV

@Remi, FWIW there are patients that PCV is better than other modes. Kind of obscure for this forum, for the obese laparoscopic surgery patient, PCV, in at least one paper that I saw, is demonstrably better than VCV (PC-volume guarantee being the best) and the reasons are all pretty intuitive.   I'll kick it your way if you're interested.


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## Carlos Danger (Feb 18, 2017)

And all this time, I thought it was magic.....

Would love to see that paper, @E tank.


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## E tank (Feb 18, 2017)

Remi said:


> And all this time, I thought it was magic.....
> 
> Would love to see that paper, @E tank.



PM'd you.


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## TXmed (Feb 18, 2017)

@E tank 

So if in PCV, PIP=Pplat

Does that mean in an bronchospastic patient with a PIP of 35 but TV are down to 2-3ml/kg, your Pplat is still 35? Or what about an obese patient, pneumo patient, etc ?


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## E tank (Feb 18, 2017)

TXmed said:


> @E tank
> 
> So if in PCV, PIP=Pplat
> 
> Does that mean in an bronchospastic patient with a PIP of 35 but TV are down to 2-3ml/kg, your Pplat is still 35? Or what about an obese patient, pneumo patient, etc ?



With the ventilators that I use, yes, and if the one's that you use are configured so that there is no flow at the end of the cycled breath, then yes there too.

Did I get your question or did I miss something?


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## TXmed (Feb 18, 2017)

@E tank you answered it sir


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## Brandon O (Feb 19, 2017)

E tank said:


> As far as "bucking" goes, if the issue were just isolated to the intrapulmonary/thoracic pressures, there would less of an issue. But it's not. It raises ICP, MAP, and the HR as well. Healthy patient? Who cares? But I don't think that's what we're talking about



If you're pointing out that patient-ventilator dyssynchrony can elevate the variables you mentioned, obviously this is true. But this is primarily a result of discomfort and sympathetic activation. I can also elevate the heart rate by vigorously poking the patient with a stick. The solution is to resolve the stimulus (i.e. adjust the vent to allow better synchrony, or increase sedation). While I certainly agree there are times when PCV is better tolerated than VCV, it sounds like you're talking about something different.

I think it is also probably untrue that raising the ICP by a purely valsalva-type mechanism is harmful per se. Just like the transpulmonary gradient, the gradient across the cerebral vessels is not elevated in this case; since the MAP and ICP elevate simultaneously there is usually no change in the CPP. IMO; obviously there may be exceptions.



> 2. What's not good? Delivering more tidal volume at a lower pressure?.



I think this is the crux of the issue here. Why would this be good?


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## Brandon O (Feb 19, 2017)

TXmed said:


> @E tank
> 
> So if in PCV, PIP=Pplat
> 
> Does that mean in an bronchospastic patient with a PIP of 35 but TV are down to 2-3ml/kg, your Pplat is still 35? Or what about an obese patient, pneumo patient, etc ?



The inspiratory pressure you set in PCV is the driving pressure created by the vent (on top of PEEP); no pressure within the airway will exceed this. Early in the breath, much of this pressure will be from airway resistance, and the "plateau" is low here (although not measurable). As flow decreases later in the breath, less of that peak figure is made up from airway resistance and more by alveolar elastance (i.e. the plateau pressure). If flow drops to zero at the end of the breath, which it should in a properly-configured PCV mode (inspiratory time must ideally be long enough to allow this), then resistance is gone and all of the peak pressure is from the plateau.

This can be a little confusing, but the point is to remember than in PCV, *we* set the total airway pressure, and the vent maintains it. What that pressure consists of, however, depends on the flow. So in a patient with high airway resistance (bronchoconstriction), you would still have the same PIP; you simply might not get much volume squeezed into each breath, and the plateau would be low (probably less than the PIP). Likewise with poor chest/lung compliance (ARDS, obesity), you will not exceed the set PIP and hence not exceed that plateau pressure, but the tidal volumes might be quite small.


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