PEEP with bare BVM

Brandon O

Brandon O

Puzzled by facies
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Would love to hear any discussion of this method of bagging, which I have never in my life encountered until hearing about it from UPitt's critical care folks. View from :24 through :55 here: http://www.ccmpitt.com/education/airway_course/videos/video2_2012.html

The idea is that, with a regular BVM (but EXCELLENT MASK SEAL, preferably two-handed), you bag as normal, but right before the end of passive expiration, you give the bag a little "pop" to arrest their expiration and re-establish positive pressure --. This essentially creates a PEEP effect, without the need for a separate PEEP valve, CPAP device, or intubation -- yet it allows unimpeded exhalation for most of the expiratory phase. They also like that it gives a good "feel" for pulmonary compliance; since you essentially have a closed system once you reestablish positive pressure, you can easily tell if you have a leak (you feel a loss of resistance or increased compliance) or breath stacking (reduced compliance).

This didn't seem possible until I played with the BVM enough, but it clearly is, although technically somewhat challenging (it requires a three-beat cycle to bag, slooow-fast-faster). Now I keep thinking it's friggin' awesome, and pretty much the only way to create PEEP (and hence address a whole lot of otherwise insoluble problems) for most BLS. Thoughts? Anyone seen this before?
 
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Make it easy for everybody and not just those that are able to keep the 3 squeeze rythym.

5cm/h20 of peep using a nasal cannula then use your BVM like normal.

http://emcrit.org/misc/bvm-preoxygenation-and-reoxygenation/

Or you can add a peep valve to your BVM, whichever your company supplies will work
 
Love EMcrit and apneic oxygenation to pieces, but most BLS units don't carry PEEP valves for the BVM, and many ALS units don't either (obviously they usually have other options, but there's a certain appeal to being able to accomplish this even without the other toys). Without the valve to provide back-pressure you won't get any PEEP from the cannula.

Supposedly on the true high-flow nasal cannulas (in the 40-60LPM ballpark), they do manage to achieve a PEEP-like effect by inspiratory pressure alone, but I don't think we're going to hit that with a regular cannula.

You can also partially occlude the outflow port of your BVM (with tape or whatever), but that's so ham-handed that I doubt I'd want to try it.
 
While watching the video, you see the pressure (via the manometer) go to zero before rising again by squeezing the bag. When ventilating a patient with a BVM, the waveform should mimic that of a mechanical ventilator, where the pressure rises through inhalation and then decreases to the baseline (your PEEP/CPAP level). The only time below the baseline in that waveform would be when the patient inhales, triggering the device. Most devices have sensitive triggers to minimize the amount of time below the baseline.

One has to consider that role of PEEP/CPAP is to maintain alveolar recruitment and prevent them from re-closing. Once the alveoli are closed, it takes more pressure to reinstate them (think of blowing up a balloon where the hardest part is at the beginning, just getting the thing started). The role of PEEP/CPAP is keeping alveoli open and then ventilating them using the lowest pressures possible. By entering a negative portion of the pressure cycle, you risk allowing them to collapse. The constant collapse/inflation cycles are what causes ARDS, from the shear forces on the tissues (they are literally being ripped apart).

On another note, if your service doesn't allow PEEP valves as a safety concern (versus just being cheap), then you should be careful trying to mimic that effect on your own. If the powers that be doesn't feel its safe, then you should avoid it. If they feel that its a worthy treatment adjunct, then I would recommend a calibrated valve instead of a work around.
 
BLS Systems Limited said:
While watching the video, you see the pressure (via the manometer) go to zero before rising again by squeezing the bag. When ventilating a patient with a BVM, the waveform should mimic that of a mechanical ventilator, where the pressure rises through inhalation and then decreases to the baseline (your PEEP/CPAP level). The only time below the baseline in that waveform would be when the patient inhales, triggering the device. Most devices have sensitive triggers to minimize the amount of time below the baseline.

One has to consider that role of PEEP/CPAP is to maintain alveolar recruitment and prevent them from re-closing. Once the alveoli are closed, it takes more pressure to reinstate them (think of blowing up a balloon where the hardest part is at the beginning, just getting the thing started). The role of PEEP/CPAP is keeping alveoli open and then ventilating them using the lowest pressures possible. By entering a negative portion of the pressure cycle, you risk allowing them to collapse. The constant collapse/inflation cycles are what causes ARDS, from the shear forces on the tissues (they are literally being ripped apart).

On another note, if your service doesn't allow PEEP valves as a safety concern (versus just being cheap), then you should be careful trying to mimic that effect on your own. If the powers that be doesn't feel its safe, then you should avoid it. If they feel that its a worthy treatment adjunct, then I would recommend a calibrated valve instead of a work around.
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Well said, and I missed the manometer there. But I'm not so sure.

Starting at the beginning of inspiration, we imagine a zero-pressure state with collapsed alveoli and poor recruitment. With inspiration (in this case, assisted or wholly via positive pressure), some of those spaces are forced open and increasingly distended.

Then we withdraw pressure. The external gradient is reversed and gas exits the lungs. Those spaces begin to shrink again.

But before they entirely collapse, we reintroduce positive pressure. We never fully return to the resting state, so alveoli remain partially distended and should not collapse. We avoid the "hard part" of inspiration -- which involved that initial inflation (Young-Laplace) and parting of surface tension -- by retaining some air through the cycle; if we graphed it spirometrically (volume against time) we'd see that after initial inflation, we've "trimmed" the bottom of the cycle and aren't ever fully expelling the full tidal volume. (This would be bad if it compounded, resulting in increasing trapping and stacking of breaths, but we should be able to reduce our ventilatory volumes correspondingly.)

I'll grant you that PEEP is usually achieved by maintaining a continuous positive pressure throughout expiration, not introducing it near the end. But it's not clear to me why that should actually be necessary if we have the capacity (using eyeballs and timing) to establish the, well, the EEP at the right moment.

As to whether this is wise, that's perhaps another discussion, but if nothing else I think you can never have too many tools available and it's worth discussing.
 
To be honest this climbs into a more esoteric place in the context of BLS/EMT BVM. While there is great utility to PEEP it is generally applied in a case-specific fashion to patients that require it. Altering BVM techniques to try and maintain some PEEP has the potential to negatively impact patients just as much as it may help. For instance, the patient with no co-morbidities who presents as a cardiac arrest will actually likely not require much if any PEEP. We speak of alveolar collapse but don't forget that atelectasis and collapse are in abnormal lungs (pulm edema, ALI/ARDS, etc). The purpose of surfactant is to maintain some alveolar integrity. If the person has no lung pathology the application of PEEP may not be as important. However with increases PEEP one obviously also increases intrathoracic pressure and this can diminish blood return or preload.

Contrast this with a person with a primary lung disease of some sort where the application of PEEP will be useful. Applying PEEP is a process that is generally guided by ABGs, volumes, etc. The amount of PEEP is just as important as just it's application. Depending on the pathology and amount of PEEP (which will be unmeasured in BVM ventilation) your compliance will decrease. If volumes are kept high (as in BVM ventilation as it is generally applied) the pressures will increase which can lead to further problems.

One last point - in many circumstances I've seen BVM ventilation tends to go rather quickly. The person at the head is sometimes distracted by everything going on and I've witnessed that the greatest impulse to squeeze the bag is when it is full. This can lead to a hyperventilation and incomplete expiration. This effect creates a type of "auto-PEEP" on it's own. Focusing on solid BVM ventilation and minimizing the chances of aspiration and allowing for complete exhalation are the keys to good BVM-ing.

K, that's a little more than I thought I'd write so excuse the blah-blah. :)
 
Agreed across the board. Indiscriminately applying any non-benign intervention (and nothing is benign) is worse than omitting it entirely. The inability to discern when it's indicated is the main argument I would accept against the BLS use of PEEP, including commercial CPAP (although I don't necessarily think EMTs can't be trained to develop that ability).

But at least theoretically, there is definitely a niche here, one that has essentially has no other solution. Let's grant that you're an EMT doing fantastic, flawless BVM ventilation -- great mask seal, perfectly patent airway, beautifully controlled rate and pressure, no gastric distension. Yet your patient is massively shunted due to, say, COPD or pulmonary edema, and as a result they're oxygenating poorly. Despite adequate ventilation with 100% O2, their sat is 83% (or barring that, they're turning increasingly blue-gray in front of you). What can you do, except do nothing and hope they make it?

Doesn't that patient need PEEP? Pharmacological interventions too probably, but those aren't available either. Presumably either you are headed for an emergency department, or paramedics are headed for you, or both, so before long more definitive measures can be applied. But until then, all you have is your little rubber bag and whatever tricks you can pop out of your noodle. I'm not saying that any given BLS provider should be out there doing this tomorrow, but I hope you can see why the possibility of a viable solution here is potentially exciting for us little people.
 
No questions that PEEP is generally useful in refractory hypoxemia. I guess the only thing I caution against, especially in a BLS context given that there may be many out there who are newer and still gaining experience is that one should not overthink a call. For instance is the SpO2 reliable or is the patient profoundly peripherally shut down? Is there a waveform or is it just a number?

I agree that given your described 'perfect storm' of awesomeness that some PEEP may help to improve oxygenation - I just wouldn't want to encourage people to look for it. In my experience with crews and as an instructor I would have to say that you can never go wrong with doing what you're trained to do to the best of your ability. The more stuff you try to remember to add on, especially on a more complex call, the more likely it is that some other part of your treatment will suffer.
 
I guess when it comes down to it, you're actually highlighting an important dichotomy. This is unquestionably an advanced technique, yet most "advanced" providers have other tools available. No doubt there are Basics who could make the BVM sing and dance, but I suppose it's not exactly the norm.

But we could always flip it, because paramedics, ED physicians, and Vishnu himself still need to be able to ventilate without an invasive airway. As Reuben Strayer has observed, you're better off if you're great at bagging and crummy at intubation than vice versa, because you can't avoid the former and it sets the stage for the latter. And isn't there something to be said for the ability to immediately provide what the patient needs when you arrive at the bedside, no matter where you expect to eventually land?
 
Brandon Oto said:
I guess when it comes down to it, you're actually highlighting an important dichotomy. This is unquestionably an advanced technique, yet most "advanced" providers have other tools available. No doubt there are Basics who could make the BVM sing and dance, but I suppose it's not exactly the norm.

But we could always flip it, because paramedics, ED physicians, and Vishnu himself still need to be able to ventilate without an invasive airway. As Reuben Strayer has observed, you're better off if you're great at bagging and crummy at intubation than vice versa, because you can't avoid the former and it sets the stage for the latter. And isn't there something to be said for the ability to immediately provide what the patient needs when you arrive at the bedside, no matter where you expect to eventually land?
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Brandon, you are a super-basic with not only the education, but also likely the skills to pull this off, but very very few basics are. The skills of GOOD BVMing skills are he'd over time, and rather than equip BLS trucks with these tools (although as mentioned, proper CPAP would be a nice tool), there is more benefit to putting those resources into education.

It would really be great to be able to McGyver an efficient PEEP valve, but it seems that's not possible. My advice to you is to go to medic or PA school so you can have these tools.
 
No doubt this isn't exactly a top priority when people are still out there every day blowing up stomachs and puzzling over how to open an airway. But I do think that, ideally, we should be striving for true mastery of our foundational tools -- all the more so the more austere our conditions and the more limited our resources. We should be able to list the melting point of our catheters and kill a velociraptor using triangular bandages.

And I like to think that foundational BLS is important at every level. When you add things on top before it's well-grounded, you'll have nothing to fall back on when things go wrong, because it wasn't there to begin with.
 
Brandon Oto said:
No doubt this isn't exactly a top priority when people are still out there every day blowing up stomachs and puzzling over how to open an airway. But I do think that, ideally, we should be striving for true mastery of our foundational tools -- all the more so the more austere our conditions and the more limited our resources. We should be able to list the melting point of our catheters and kill a velociraptor using triangular bandages.

And I like to think that foundational BLS is important at every level. When you add things on top before it's well-grounded, you'll have nothing to fall back on when things go wrong, because it wasn't there to begin with.
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That's a justification for bringing EMTs into skills labs or simulation labs (?ever?), or at least more often. I've been very lucky to be able to spend a lot of time in both in the last few weeks, and found my BLS airway management skills to have improved 300%. With that said, even solidifying these basic skills has been time consuming and difficult at times. When we don't find any of these true skills being introduced, yet alone mastered in original EMT programs, it's difficult to mandate them for practicing EMTs.

As it stands, there is no financial or legal impetus for employers (at least private ambulance companies) to provide true education to their employees. I'm not saying it doesn't exist, but this true education and skill development is the extreme minority, at least of providers i've seen.

Brandon, how often do you have access to, or practice BLS airway skills at your employer?

I hate to say this, but if we're going to talk about honing BLS airway skills, we also need to approach ALS airway competence, and think about getting those who provide more invasive therapies more practice with their skills.
 
Can't argue with any of that.

We have a Sim-Man but it's not something we can walk in and play with. Lots of CPR dummies that you can bag, but not manipulate the airway (beyond simple head extension), insert pharyngeal airways, or anything more elaborate.

I recently discovered that you can bag a kettlebell, however, and measure positive pressure using a sphygmomanometer gauge. So that's something.
 
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