# Why does an adult BVM have a 1600ml capacity?



## DragonClaw (Aug 4, 2019)

I mean,  it takes 500ish mlS to inflate lungs and I read a lot that hyperventilation easily happens by getting a little too trigger happy with a BVM, so why the heck are that that big?

At what time do you need to squeeze as hard and fast as you can?


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## GMCmedic (Aug 4, 2019)

Im sure there is a legit answer but look how long it takes us to adopt evidence based practice. It takes manufacturers even longer.


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## E tank (Aug 4, 2019)

Easier to partially squeeze a big bag than completely collapse a small one.


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## NPO (Aug 4, 2019)

Because you're not supposed to compress it like a vice. Easier to squeeze 400-500ml out of 1500. Than 500 put of 500.


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## Summit (Aug 4, 2019)

Most are too big for smaller providers to get their hands comfortably around IMO thus the proliferation of softer materials.


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## VFlutter (Aug 4, 2019)

To compensate for air leak with poor seal during mask ventilation


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## Carlos Danger (Aug 5, 2019)

Because what are you supposed to do, deliver 100% of the bags volume with every breath?


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## E tank (Aug 5, 2019)

Bags on anesthesia machines are 3 liters.


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## DragonClaw (Aug 5, 2019)

Remi said:


> Because what are you supposed to do, deliver 100% of the bags volume with every breath?


To be honest a 1 squeeze=1 breath seems simple. Yeah. 

But then if the person had really big lungs..?


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## Tigger (Aug 5, 2019)

Do you think you can squeeze every bit of that capacity into the patient?


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## DragonClaw (Aug 5, 2019)

Tigger said:


> Do you think you can squeeze every bit of that capacity into the patient?



I'm going to go and rethink my life.  That's what I now think. 

I guess I thought I could? But,  I guess... no?


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## Carlos Danger (Aug 5, 2019)

DragonClaw said:


> To be honest a 1 squeeze=1 breath seems simple. Yeah.
> 
> But then if the person had really big lungs..?



The point is that you are only reasonably going to be able to use the a certain percentage of the breathing bag's volume. So if you want to deliver 500ml of vt, you need a bag with more volume than that. Not to mention, as someone else did, that a larger volume with a self-inflating bag gives you the ability to continue to deliver volume after making a mid-breath adjustment to your mask seal or positioning. 

Bottom line is that the volume you give should not be determined by the size of the bag you are using. Slowly give enough volume to cause visible chest rise, pause for a short moment, and let go. Do that over a 6 second cycle. Use capnography if you have it available.


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## DragonClaw (Aug 5, 2019)

Remi said:


> The point is that you are only reasonably going to be able to use the a certain percentage of the breathing bag's volume. So if you want to deliver 500ml of vt, you need a bag with more volume than that. Not to mention, as someone else did, that a larger volume with a self-inflating bag gives you the ability to continue to deliver volume after making a mid-breath adjustment to your mask seal or positioning.
> 
> Bottom line is that the volume you give should not be determined by the size of the bag you are using. Slowly give enough volume to cause visible chest rise, pause for a short moment, and let go. Do that over a 6 second cycle. Use capnography if you have it available.



Yeah,  in school,  with a BVM it's taught you can tell you're properly ventilating with "Equal and bilateral chest rise"

Nobody mentioned capnography,  but that would make sense to use.


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## ThadeusJ (Aug 6, 2019)

They were developed back in the day when you ventilated with 10-15 ml/kg, and we have kept those sizes.  For a standard 1500 mL adult BVM, the one hand stroke volume is still 850 mL while the two hand effort can reach 1150 mL.  You could probably vent using a pediatric bag (600 and 740 mL, respectively), however if you wanted a higher volume for whatever reason, you wouldn't have access to it.  Also, the elastic recoil during re-inflation is more responsive when partially evacuating the bag than if you emptied it fully.  

Another factor is that during the purchasing process, the tenders generally specify very tight measurements, so essentially the customer spec's in the same adult size every year and that's what the distributor provides.  

If you are  concerned about over-ventilating the patient, you might want to consider one of the adult BVM's with a pressure relief valve incorporated into it.


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## Peak (Aug 7, 2019)

Keep in mind that equipment is used in environments beyond just field EMS. 

I've had a couple of patients who we have resuscitated with over 60 mmHg of inspiratory pressure and 40mm of PEEP (granted we use flow inflating bags for this). These are patients who are so rigid that we are running mean pressures in the high 30s on the ossilator and are on NMBDs. There are times where you need a larger bag to get a good purchase on it and be able to deliver the volume, we typically use a 1 liter bag on infants and a 2 liter on kids and adults. 

There is always going to be and aspect of leak, whether you are using a self inflating bag, flow inflating bag, a vent, or anything else. You will leak around peep valves, loose connections, the mask seal, and the tube/cuff. I've had adults with cuffed trachs (and pretty generous cuff pressure) who still required us to deliver almost the entire volume of an adult BVM in order to give a breath. 

If the patient isn't intubated/trached you are probably gonna be putting some air into their stomach, even with good technique. If it is allowed in your scope and not otherwise contraindicated I would consider placing an OG/NG early in resuscitation. Not only are you going to prevent them from aspirating, but by decompressing the belly you will allow more room for the lungs to expand and give you an opportunity at better ventilation.


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