How much does a BVM increase WOB?

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usalsfyre

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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.
 
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.
 
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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.
 
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however we add PEEP valves to the bags themselves.
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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.
 
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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.
 
Ya'll are pretty well confirming my suspicion that this was developed without the input of Respiratory or Anesthesia
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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.
 
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.
 
using a BVM with a PEEP valve is a poor-man's CPAP
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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".
 
What if you use your BVM with a peep valve with a NC under the mask at 15 liters?
 
Bobbob1354 said:
What if you use your BVM with a peep valve with a NC under the mask at 15 liters?
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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.
 
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.
 
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.
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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/
 
The sealed BVM will also fill the hypopharynx. In modern, disposable BVMs there's a relatively constant flow of gas in.
 
usalsfyre said:
The sealed BVM will also fill the hypopharynx. In modern, disposable BVMs there's a relatively constant flow of gas in.
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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.
 
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.
Click to expand...

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?
 
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.
 
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.
 
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