NRB question

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I need some clarification on how the NRB works and how flow rates affect oxygen delivered. As I understand it right now the correct flow rate is that of which keeps the bag inflated (10-15 LPM). So say you are providing o2 at 10 LPM and the bag is remaining full. Would increasing the flow rate increase the percent of oxygen delivered? I don't think it would seeing that the bag isn't collapsing, but I'm not sure.
 
Room air is 21% oxygen. O2 cylinders contain 100% oxygen. NRBs deliver anywhere from 60-80% oxygen to the patients lungs. There are many variables beyond flow rate that determine FiO2 of a NRB.

FiO2 is a measure of percent of oxygen in a mixture. You can dial in a specific FiO2 with vents but with NRBs it's kind of a crap shoot what your patient is actually getting.

In the field, if your patient is hypoxic a NRB anywhere between 10-15L/m would be acceptable.
 
Now you've done it and opened this can of worms (for me anyways). If all the valves are present (one at the reservoir bag and two on the side of the mask for exhalation), the mask should direct oxygen towards the patient in inhalation and out the sides on exhalation. Due to no anti-suffocation protection, many jurisdictions mandated the removal of one of the one way exhalation valves. This allowed the patient to breath in a significant amount of oxygen through the (once dedicated) exhalation port. Although most textbooks state that in theory these devices will deliver 80-95% oxygen, actual studies (which I also used to demonstrate in another life) reveal that the patient actually receives just as much room air as oxygen. This is down to the 60% range. I would urge you to Google up Garcia (CHEST 2005), Moody (AARC Open Forum 2007), and/or Earl (AARC Open Forum 2003) to see their results. These masks perform so poorly that Standley (Intens Care Med, 2008) concluded that hospitals wishing to deliver specialty gas mixtures to patients shouldn't use conventional NRB because of the room air dilution.

So why do we still use them? Most patients don't actually need true 100% oxygen, however those who continue to deteriorate are provided a disservice by those who think they are providing as much as they can when in fact they do not. These are inexpensive disposable devices that get us through the day. If you look at your textbooks, most say the same words and quote theory as opposed to practice. We write what they want to hear on exams about oxygen delivery, so we are all saying the same thing.
 
ThadeusJ said:
Now you've done it and opened this can of worms (for me anyways). If all the valves are present (one at the reservoir bag and two on the side of the mask for exhalation), the mask should direct oxygen towards the patient in inhalation and out the sides on exhalation. Due to no anti-suffocation protection, many jurisdictions mandated the removal of one of the one way exhalation valves. This allowed the patient to breath in a significant amount of oxygen (((((YOU MEAN AIR???))))) through the (once dedicated) exhalation port. Although most textbooks state that in theory these devices will deliver 80-95% oxygen, actual studies (which I also used to demonstrate in another life) reveal that the patient actually receives just as much room air as oxygen. This is down to the 60% range. I would urge you to Google up Garcia (CHEST 2005), Moody (AARC Open Forum 2007), and/or Earl (AARC Open Forum 2003) to see their results. These masks perform so poorly that Standley (Intens Care Med, 2008) concluded that hospitals wishing to deliver specialty gas mixtures to patients shouldn't use conventional NRB because of the room air dilution.

So why do we still use them? Most patients don't actually need true 100% oxygen, however those who continue to deteriorate are provided a disservice by those who think they are providing as much as they can when in fact they do not. These are inexpensive disposable devices that get us through the day. If you look at your textbooks, most say the same words and quote theory as opposed to practice. We write what they want to hear on exams about oxygen delivery, so we are all saying the same thing.
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They're used because unless you're using a totally closed system, it's probably the best way to deliver the highest O2 concentration to the patient. It's certainly better than a nasal cannula or simple face mask. If you truly entrain as much air as oxygen (not sure I believe that, and of course that's why the higher O2 flows are important) then the 60% number would be accurate.
 
Thanks for the correction about the air and oxygen and yes 60% is a 1:1 mix of room air and oxygen. As some of those studies show, even turning the oxygen flow up to ridiculously high levels still results in room air dilution because of the mask design. I find it funny that if we were to use a BVM at 15 LPM, you would see the reservoir bag collapse and expand with each delivered breath. But using a NRB, you don't see the same movement in the reservoir bag, which would indicate that the breath is being satisfied by room air.
 
ThadeusJ said:
I find it funny that if we were to use a BVM at 15 LPM, you would see the reservoir bag collapse and expand with each delivered breath. But using a NRB, you don't see the same movement in the reservoir bag, which would indicate that the breath is being satisfied by room air.
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I always thought that was because the flow rate filling the reservoir was greater than the inspiratory flow rate . So the patient is still getting supplimental O2
 
That's exactly what the reservoir is for. But with the NRB, the bag doesn't fluctuate as much as the BVM. Once you remove one of the side valves, the reservoir should fluctuate as much or more with each breath. I used to put tape over the open exhalation port and have the patient exhale through the one valved port and you would see a noticeable difference in the way the reservoir moved with each breath. The reservoir should give you an indication whether the patient is receiving 100% oxygen or is entraining room air.
 
Fill the bag (CRITICAL FAIL!!!)
Put pt on NRB
Monitor for signs of improvement or deterioration.
Address issues as needed.

Otherwise, there may be a bit too much thought involved.
 
ThadeusJ said:
That's exactly what the reservoir is for. But with the NRB, the bag doesn't fluctuate as much as the BVM. Once you remove one of the side valves, the reservoir should fluctuate as much or more with each breath. I used to put tape over the open exhalation port and have the patient exhale through the one valved port and you would see a noticeable difference in the way the reservoir moved with each breath. The reservoir should give you an indication whether the patient is receiving 100% oxygen or is entraining room air.
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I'm not following....

With a flow rate well above inspiratory flow rate, you would see minimal movement of the reservoir bag no matter what.
 
gotshirtz001 said:
Fill the bag (CRITICAL FAIL!!!)
Put pt on NRB
Monitor for signs of improvement or deterioration.
Address issues as needed.

Otherwise, there may be a bit too much thought involved.
Click to expand...
If you're taking NREMT then this post would be relevant, however the OP mentions nothing about NREMT...
 
Agreed, but the peak inspiratory flow rate of the patient is upwards of 60-150+ LPM, which isn't possible from a standard flowmeter (many DISS demand valves should go up to the 160 LPM range) but not Thorpe tube or cylinder regulators. The idea of the reservoir bag is to deliver a volume of gas equivalent to the volume inhaled during the inhalation phase, filling on the exhalation portion of the breath. If the bag isn't decreasing in volume during inhalation then you must assume that the breath is being satisfied solely by the gas inflow (thereby making the reservoir redundant) or else the patient is breathing room air.
 
Ok I think I understand your point now.

If the reservoir isn't deflating we can't know if the patient is breathing the O2 or plain room air, so decrease the flow to make sure ventilations are coming from the reservoir. Is that right?
 
Exactly. In a perfect world, the bag would deflate completely before any room air is inhaled. The mask volume itself is pretty small so any oxygen in that small space provides minimal benefit and the removal of the one side valve essentially destroys the functionality of the mask. As I said earlier, most patients are OK with this and do well, however for those who continue to deteriorate, we should be aware of this concern.
 
ThadeusJ said:
Exactly. In a perfect world, the bag would deflate completely before any room air is inhaled. The mask volume itself is pretty small so any oxygen in that small space provides minimal benefit and the removal of the one side valve essentially destroys the functionality of the mask. As I said earlier, most patients are OK with this and do well, however for those who continue to deteriorate, we should be aware of this concern.
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With reasonable mask fit, you should be seeing some movement of the bag. There's no problem taping the open valve if you want. Regardless, I think you're getting a higher concentration with this than you will with a nasal cannula or simple facemask.

Also - remember that lots of BVM's have a reservoir tube or bag as well, so even they may not be giving you 100%, depending on your O2 flows.
 
One of the biggest fears is having the flow titrated down so low that it doesn't flush out the exhaled CO2. You would see a fogging on the inside of the mask around 4-6 LPM. Although we always want to emulate what we see on TV and in the movies (he says with sarcasm) , it should never happen.
 
Simple fixes: use masks with full valving (or cover the hole if you're bold), actually tighten the mask until it seals (or have the pt seal it), increase flow, put a cannula under there, use a BVM instead.

Not a good fix: holding a BVM on or near the face. Does not provide high flow.
 
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