# How much does a BVM increase WOB?



## usalsfyre (Jan 21, 2011)

I've got conflicting reports over the technique we use to preoxygenate patients prior to airway control. Currently we use a BVM with 10cm of PEEP on 25lpm O2 sealed over the patient's face. The preferred method is to simply let the patient breathe through the bag to prevent gastric distension. 

I've used it several and it's worked well, SpO2 levels have increased, ETCO2 numbers have gone down and the patient's coloring has improved. However, I've also read many reports and opinions that this seriously increases the work of breathing due to having to overcome the resistance of the BVM. It would seem much harder to breath through a self inflating bag vs an anesthesia bag due to the size and stiffness of the BVM. 

Anyone have any evidence one way or the other? I really wonder how much of the improvement had been due to PEEP and ultra high-concentration oxygen vs the supposed "mask seal assisting in O2 delivery to the alveoli" and if we couldn't achieve the same thing with our CPAP setup.


----------



## Journey (Jan 21, 2011)

One of the first things you should have learned is that a self inflating BVM is NOT to be used as CPAP. If offers no "Continuous Positive Airway Pressure" and requires at least 20 cmH2O of pressure to open the value with a totally sealed circuit which is very difficult on the human face.   NRP and PALS classes definitely stress this.  

The Jackson Rees circuit (anesthesia) is what hospitals may use for pre-oxygenation of patients for intubation in the ICUs and EDs.  

I suggest you attempt this on youself with another EMT and feel the discomfort of the extreme pressure and suffocation of struggling for each breath.  It is sad to see patients faces bruised for no reason except someone did not know the proper use of a BVM.  Also, read the manufacturer's recommendations for the BVM you are using. Exceeding the recommended flows can damage the BVM and cause it to malfunction.  

The ETCO2 may also go down due to an increased WOB initially with a "hyperventilation" affect and the SpO2 may go up for a short time. However if you measure lactate after an extended period of time, you may find an increase and it can also lead to failure or the eventual crash and burn.


----------



## usalsfyre (Jan 21, 2011)

I've tried it and not found it to be especially uncomfortable, that said I didn't have pathology at the time either. I'm also not sure we're doing an especially great job sealing them, EMS (and most other healthcare providers for that matter, outside of respiratory and and anesthesia) are notorious for cr@ppy mask seals. 

It's currently protocol/guideline, but if it's doing more harm than good, we need to see about getting it changed.

Edited to add: I understand a BVM in and of itself is not CPAP, however we add PEEP valves to the bags themselves.


----------



## usafmedic45 (Jan 21, 2011)

> however we add PEEP valves to the bags themselves.



But there is no flow to the patient except when the bag is squeezed.  Basically you're asphyxiating the patient.

It's not CPAP using a BVM regardless of whether you have a PEEP valve or not.

Is it just me or is there a new rumor making the rounds that you can deliver CPAP with a BVM?  It seems like a lot of people are doing some really questionable things (bordering on the stupid) because of a fundamental misunderstanding of mechanical ventilation.


----------



## usalsfyre (Jan 21, 2011)

Ya'll are pretty well confirming my suspicion that this was developed without the input of Respiratory or Anesthesia, who should have been the go to departments for this. So, based on our current equipment (NRB, Boussignac, CPAP or BVM delivering breaths this time), what would recommend using for preoxygenation? I'd love to have the option of going to something better for the task, but currently, it's just not an option in our system. Maybe in a few months, but until some other business is attended to we're stuck where we're at.


----------



## usafmedic45 (Jan 21, 2011)

> Ya'll are pretty well confirming my suspicion that this was developed without the input of Respiratory or Anesthesia



You mean the PEEP valve?  Actually they have been around a very long time (these devices were part of a free-flowing circuit originally used to give CPAP).  Their use on BVMs actually has a benefit in a closed system (read as: intubated patient).  Using one on a patient who is not tubed yet is about as pointless as it gets because you're not going to maintain the airway pressures you are trying to achieve (both because of poor mask seal (even when you have "great mask seal") and because of the presence of the esophagus). 

If the patient is ventilating adequately, NRB.
If the patient is not ventilating adequately, BVM. 
Don't waste time trying to do *proper* CPAP if they are not protecting their airway.  It's not an preoxygenation tool.  It's only used in people who can protect their own airway and for those situations where a relatively short term course of ventilatory assistance is likely to result in improvement in the patient's condition (asthma/COPD exacerbation, CHF/pulmonary edema, etc).

Let me reiterate this again so there is no mistake:  You CANNOT give CPAP through a BVM.  If you're ventilating with a BVM, that elevated baseline pressure you get with a closed circuit (intubated patient) is PEEP.  The patient CANNOT breath adequately through a BVM (because of the "valve" part of bag-valve-mask) and anyhow, you're not going to maintain an elevated pressure because of the tendency of patients to swallow air when not intubated.


----------



## Akulahawk (Jan 22, 2011)

At *best*, using a BVM with a PEEP valve is a poor-man's CPAP. As usafmedic45 has said... you're not going to be able to maintain an elevated pressure because of poor mask seal and that people tend to swallow air when not intubated. I've used it to assist someone by tracking their respirations, but that's not exactly going to last all that long. I'd call it a red-headed :censored::censored::censored::censored::censored::censored::censored:ized step-child version of what's not exactly CPAP. I'd rather have someone on a formal CPAP or BiPAP unit... or intubate them, if they're in need of assistance that will last more than a couple minutes.


----------



## usafmedic45 (Jan 22, 2011)

> using a BVM with a PEEP valve is a poor-man's CPAP



No, it's not.  Please don't tell people that.  It does not maintain a baseline and patients cannot breathe spontaneously while on it.  Therefore, it is NOT CPAP in any way.  Do not in any way shape or form encourate this sort of "treatment".


----------



## Bobbob1354 (May 29, 2016)

What if you use your BVM with a peep valve with a NC under the mask at 15 liters?


----------



## Akulahawk (May 30, 2016)

Bobbob1354 said:


> What if you use your BVM with a peep valve with a NC under the mask at 15 liters?


Much of the time that I read about use of the NC at 15 liters, it's as part of an apnic oxygenation process in preparation for endotracheal intubation.


----------



## Carlos Danger (May 30, 2016)

Bobbob1354 said:


> What if you use your BVM with a peep valve with a NC under the mask at 15 liters?



Why would you do such a thing?


----------



## Bobbob1354 (May 30, 2016)

Remi said:


> Why would you do such a thing?


You can use the nc to fill the hypopharynx as a oxygen reserve.


----------



## Carlos Danger (May 30, 2016)

Bobbob1354 said:


> You can use the nc to fill the hypopharynx as a oxygen reserve.



But why would you place it under a BVM?


----------



## Bobbob1354 (May 30, 2016)

So the continuous flow of the nc under the bvm mask will fill the hypopharynx in between ventilation. Some of that o2 will also diffuse down its gradient into the lower airways.


----------



## Bobbob1354 (May 30, 2016)

Akulahawk said:


> Much of the time that I read about use of the NC at 15 liters, it's as part of an apnic oxygenation process in preparation for endotracheal intubation.


I have heard that too, but is it possible that with a bvm, peep valve and nc that you could create a sort of cpap? Im not 100% on this but when ventilating you would create pressure, when exhaling you would keep some residual pressure in, and with the constant flow of a nc there would be some pressure left. Here is a video on apneic oxygenation too.

http://emcrit.org/blogpost/apneic-cpap-recruitment-demonstration-george-kovacs/


----------



## usalsfyre (May 30, 2016)

The sealed BVM will also fill the hypopharynx. In modern, disposable BVMs there's a relatively constant flow of gas in.


----------



## Bobbob1354 (May 30, 2016)

usalsfyre said:


> The sealed BVM will also fill the hypopharynx. In modern, disposable BVMs there's a relatively constant flow of gas in.


That is true but the nc at 15 liters increases pressure relative to that created by the bvm alone, promoting more diffusion down the airway.


----------



## Carlos Danger (May 30, 2016)

Bobbob1354 said:


> So the continuous flow of the nc under the bvm mask will fill the hypopharynx in between ventilation. Some of that o2 will also diffuse down its gradient into the airways.



The idea of adding a NC throughout the peri-intubation process is fine, but I don't see why you'd need to use one in conjunction with a BVM. If you are using the BVM properly, plenty of oxygen will reach the lungs during the positive pressure breaths, and the positive pressure will do much more for oxygenation than passive flow will. A cannula in place will also make it harder to maintain a mask seal.

A BVM should only be used to provide positive pressure ventilations, for a couple of reasons. The main reason is that the flutter valve is not designed to open to negative pressure, so spontaneously breathing with a BVM strapped tightly to your face will significantly increase your work of breathing. Maybe some newer bags are designed for that, I don't know. Another reason is that flow demands in a spontaneously breathing patient can potentially be greater than what a BVM can provide.

The other problem with these pseudo-CPAP setups is that unlike with a device designed to provide CPAP, it is impossible to regulate the amount of positive pressure being applied to the airway.

Avoiding positive pressure in the non-NPO, unprotected airway is the whole reason we are doing RSI in the first place, right?


----------



## Carlos Danger (May 30, 2016)

A cannula underneath a NRB? Sure, I guess. But underneath a BVM? That makes no sense because if you are using the BVM to give positive pressure breaths, you just don't need the cannula - all it will be doing is getting in your way. And if you are using the BVM to provide CPAP, well, you probably shouldn't be.


----------



## Bobbob1354 (May 30, 2016)

Its not so much that you need to, its just another option for you to use. When you are having a hard time getting the o2 sat up on a patient someone can give it a try. That flow demand can be assisted possibly by a nc under the mask. Some of the bvm have manometers on them also, so you can see the pressure you are exerting. As long as when ventilating you stay near 15 mmHg you don't have to worry about opening the esophageal sphincter.


----------



## Bobbob1354 (May 30, 2016)

The nasal cannula is small enough in diameter to get a seal around the mask.


----------



## Carlos Danger (May 30, 2016)

Bobbob1354 said:


> Its not so much that you need to, its just another option for you to use. When you are having a hard time getting the o2 sat up on a patient someone can give it a try. That flow demand can be assisted possibly by a nc under the mask. Some of the bvm have manometers on them also, so you can see the pressure you are exerting.


If you are having trouble getting the Sp02 up despite adequate Fi02 and minute volume, then you need positive pressure because the problem is atelectasis, which no amount of flow will do anything to fix.



Bobbob1354 said:


> As long as when ventilating you stay near 15 mmHg you don't have to worry about opening the esophageal sphincter.



Well, if you "don't need to worry about opening the esophageal sphincter", then why mess with CPAP - why not just BVM them? And why are we even doing an RSI if we aren't worried about pressurizing the gut?

But actually, you *do* need to worry about it - because good luck getting good tidal volumes while consistently keeping airway pressures below 15 in many patients, especially those that are atelectatic.



Bobbob1354 said:


> The nasal cannula is small enough in diameter to get a seal around the mask.



It doesn't make it any easier though, and mask ventilation is hard enough in many patients, especially for people who don't do it much.


----------



## Carlos Danger (May 30, 2016)

edit


----------



## Bobbob1354 (May 30, 2016)

Remi said:


> If you are having trouble getting the Sp02 up despite adequate Fi02 and minute volume, then you need positive pressure because the problem is atelectasis, which no amount of flow will do anything to fix.
> 
> 
> 
> ...



With just a bvm you are not maximizing your minute volume you are only using what your bvm can put out, with a nc involved you are getting a higher amount of minute volume and the Fi02. A bvm, peep valve and nc have a possibility of correctly the atelectasis by using that continuous pressure to hold the alveoli open.

Because you might want a definitive airway. Also if you happen to overcome the esophageal sphincter once it becomes easier to do it again, this might increase the chance of gastric inflation. A BVM alone will not provide CPAP.

If that is the case then yeah you will have to chance going over 15 mmHg. Its just a tool to help you ventilate, but it is not a know all on ventilation effectiveness.


----------



## Brandon O (May 30, 2016)

Like many easily-misunderstood concepts, this notion of cannula-under-BVM-with-PEEP may have originated with Scott Weingart. He has some info (and a demonstration video) here: http://emcrit.org/preoxygenation

The idea is essentially that PEEP is invaluable to help oxygenate many patients with some shunt physiology, but that when using it to assist spontaneous breathing (if that's your preferred method of preoxygenation), it is imperfect because you lose the PEEP once the expiratory flow falls too low to actuate the simple spring-loaded valve. And it will, since in normal breathing flow falls to zero by the end of expiration. (To help understand this, reflect on the fact that a totally apneic person will not have any PEEP even with a PEEP valve -- it provides resistance to expiratory flow, but nothing in the absence of flow.) So he advises keeping the cannula you already had applied (per his teaching), leaving it at high flow, and it will maintain enough flow in the circuit to use the valve.


----------



## Carlos Danger (May 30, 2016)

Brandon O said:


> Like many easily-misunderstood concepts, this notion of cannula-under-BVM-with-PEEP may have originated with Scott Weingart. He has some info (and a demonstration video) here: http://emcrit.org/preoxygenation
> 
> The idea is essentially that PEEP is invaluable to help oxygenate many patients with some shunt physiology, but that when using it to assist spontaneous breathing (if that's your preferred method of preoxygenation), it is imperfect because you lose the PEEP once the expiratory flow falls too low to actuate the simple spring-loaded valve. And it will, since in normal breathing flow falls to zero by the end of expiration. (To help understand this, reflect on the fact that a totally apneic person will not have any PEEP even with a PEEP valve -- it provides resistance to expiratory flow, but nothing in the absence of flow.) So he advises keeping the cannula you already had applied (per his teaching), leaving it at high flow, and it will maintain enough flow in the circuit to use the valve.



Ok, so we are talking about maintaining PEEP in a patient receiving positive pressure ventilation, NOT using a BVM for CPAP in a spontaneously breathing patient? That is a very different animal. PEEP and CPAP are not the same thing, @Bobbob1354 . 

I suppose the idea of using a cannula to maintain flow under a BVM mask makes sense in theory, but it just seems like another one of those gimmicky things that adds steps and complexity and works like you want it to once in a while, only when all the stars have aligned just right. 

I can't help but think that if we focused as much energy on the basics of airway management as we do on these neato tricks and work-arounds, that we would have no need for neato tricks and work-arounds.


----------



## Bobbob1354 (May 30, 2016)

Remi said:


> Ok, so we are talking about maintaining PEEP in a patient receiving positive pressure ventilation, NOT using a BVM for CPAP in a spontaneously breathing patient? That is a very different animal. PEEP and CPAP are not the same thing, @Bobbob1354 .
> 
> I suppose the idea of using a cannula to maintain flow under a BVM mask makes sense in theory, but it just seems like another one of those gimmicky things that adds steps and complexity and works like you want it to once in a while, only when all the stars have aligned just right.
> 
> I can't help but think that if we focused as much energy on the basics of airway management as we do on these neato tricks and work-arounds, that we would have no need for neato tricks and work-arounds.



I understand that PEEP and CPAP are two different things. What I am saying is that the combination of the bvm, peep valve and nc make a sort of cpap over all. If  you maintain PEEP in a patient then you are providing a continuous positive airway pressure.


----------



## NomadicMedic (May 30, 2016)

Bobbob1354 said:


> I understand that PEEP and CPAP are two different things. What I am saying is that the combination of the bvm, peep valve and nc make a sort of cpap over all. If  you maintain PEEP in a patient then you are providing a continuous positive airway pressure.



No you're not. When you're not squeezing the bag you're not proving the continuous airway pressure that's provided by CPAP. You're only ventilating with PEEP and unnecessarily increasing the fi02 with the nasal cannula. If the patient needs CPAP, use CPAP.


----------



## Brandon O (May 30, 2016)

Remi said:


> Ok, so we are talking about maintaining PEEP in a patient receiving positive pressure ventilation, NOT using a BVM for CPAP in a spontaneously breathing patient?



No, not necessarily, although it would apply there too. As I understand it this is mainly for preoxygenating the spontaneously breathing patient prior to RSI, particularly when they are difficult to properly oxygenate due to shunt. Actual CPAP/BiPAP (or doing it with the vent) is another option but more logistically difficult, so he came up with this. A PEEP valve alone is good but in theory he's right that (unless the patient is auto-PEEPing, i.e. beginning their next breath before fully exhaling the previous) PEEP will drop to zero at some point during the respiratory cycle.



> I suppose the idea of using a cannula to maintain flow under a BVM mask makes sense in theory, but it just seems like another one of those gimmicky things that adds steps and complexity and works like you want it to once in a while, only when all the stars have aligned just right.



Well, I can't speak for the gentleman, and I haven't tried it myself. Most of Dr. Weingart's ideas are worth attention, even if they're not for everyone. I tend to feel that using the BVM to preoxygenate in general is rather finicky and does increase work of breathing, but the specific problem he describes is a real one without too many good solutions.


----------



## Brandon O (May 30, 2016)

DEmedic said:


> No you're not. When you're not squeezing the bag you're not proving the continuous airway pressure that's provided by CPAP. You're only ventilating with PEEP and unnecessarily increasing the fi02 with the nasal cannula. If the patient needs CPAP, use CPAP.



With a valve and an adequate flow through the cannula you do have some PEEP. Take a look at the video on the page I linked where it's demo'd using a cufflator to check pressure within the circuit. He gets a nadir of 5ish cmH2O or around there.


----------



## Bobbob1354 (May 30, 2016)

To add onto that video here is the technique used on a cadaver.

http://emcrit.org/blogpost/apneic-cpap-recruitment-demonstration-george-kovacs/


----------



## Carlos Danger (May 31, 2016)

Brandon O said:


> Well, I can't speak for the gentleman, and I haven't tried it myself. Most of Dr. Weingart's ideas are worth attention, even if they're not for everyone.



I would agree that anything Weingart says is worth considering. He's a very smart guy who spends a lot of time thinking about how to do things better, and he comes up with lots of interesting ideas.

It's one thing to come up with ideas for new techniques though, and quite another to promote the use of unproven, Macgyver-ed together interventions as standard practice (Dr. Weingart really jumped the shark, for instance, when he claimed that a normal BVM with a cannula underneath was unequivocally superior to a Mapleson circuit for preoxygenation), especially when so many people take what he says as gospel without really having a good understanding of the relevant concepts.  

I think the NC under-the-BVM thing as a way to maintain PEEP is interesting, even if I disagree with using a BVM in a patient with an adequate spontaneous minute volume. Just like apneic oxygenation and all the new bougie tricks and DSI, the concept has merit and maybe it'll be helpful in some patients. But it is far from proven, and I strongly doubt it is better than simply having the right equipment and the right skills in the first place.


----------



## Harleyjon (Jun 1, 2016)

Instead of trying to Macgyver together some "maybe it will work, maybe it wont" we simply have disposable CPAP headgear on our rigs. Sounds like a lot of back and forth over nothing.


----------



## NUEMT (Jun 2, 2016)

Remi said:


> But why would you place it under a BVM?




EMcrit published on this in Annals and here is a video.  He also just recently went over it again.  Just do a search.

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


NC under the BVM is basically the whole point..  also Peep.


----------



## NUEMT (Jun 2, 2016)

Remi said:


> It's one thing to come up with ideas for new techniques though, and quite another to promote the use of unproven, Macgyver-ed together interventions as standard practice (Dr. Weingart really jumped the shark, for instance, when he claimed that a normal BVM with a cannula underneath was unequivocally superior to a Mapleson circuit for preoxygenation), especially when so many people take what he says as gospel without really having a good understanding of the relevant concepts.




He didn't jump.  It was accepted for publication.


----------



## Carlos Danger (Jun 2, 2016)

NUEMT said:


> He didn't jump.  It was accepted for publication.


You didn't even read my whole comment, did you?


----------



## NUEMT (Jun 2, 2016)

You mean the part where you refer to Bougie and DSI as tricks?   Ya I read that.

You never disappoint


----------



## Carlos Danger (Jun 2, 2016)

NUEMT said:


> You mean the part where you refer to Bougie and DSI as tricks?   Ya I read that.
> 
> You never disappoint



Look, a little advice: misquoting someone intentionally is unprofessional, dishonest, and craven. You just did it twice, and It makes it look like either you want to have a seat at the table but aren't capable of articulating a more constructive response, or are just trolling for an argument. It will get you ignored by everyone. 

So if you want to be taken seriously, read others' posts more carefully before you reply to them, or ask for clarification of what they meant before making an assumption and calling them out in an underhanded way. Otherwise don't reply at all, at least not to the serious conversations.

You certainly don't have to agree with everything that I or anyone else says or writes, but you do have a responsibility not to intentionally misrepresent what someone said in an attempt to make them look like an idiot.


----------



## NUEMT (Jun 2, 2016)

You are right. Sorry.



Now go get your shinebox.


----------

