How much does a BVM increase WOB?

[Bobbob1354]

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

 

[Carlos Danger]

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.

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.

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]

edit

 

[Bobbob1354]

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.



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.



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.

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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

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

 

[NUEMT]

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

You never disappoint

 

[Carlos Danger]

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]

You are right. Sorry.



Now go get your shinebox.