Running out of o2

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joeboo

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Anyone know the formula to calculate how many minutes of o2 you have in a portable bottle or main bottle till reaching safe residual pressure (200 psi)?

I had an LDT where we came close to running out of o2. want to be sure next time.

Thanks
 
There is no real formula. There are too many variables. What is the flow rate? What is the patients' tidal volume? What device are you using to deliver O2? What is the temprature?

There are charts that will give you an estimate usually based on 4lpm and 12lpm.

Realistically, you need to plan ahead. If you know you have a long distance transport then it might be prudent to find out how your patient needs oxygen. A nasal cannula will last longer than a NRB.

We carry 3 - 6 D tanks and 1 - 2 M tanks on our rigs.
 
Of course there's a formula.

You first have to know the constant of the tank.

D cylinder 0.16
E cylinder 0.28
M cylinder 1.56
H cylinder 3.14

Take the constant multiplied by the tank PSI-200 (for safe residual pressure) divided by the flow rate.

For example, 0.16*2000-200/10.

A full D tank with 2000 psi will last 28 minutes if you're flowing 10lpm, leaving you 200psi in the tank.

Make sense?
 
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Glad I refreshed the page before I typed all that :P
 
leoemt said:
There is no real formula. There are too many variables. What is the flow rate? What is the patients' tidal volume? What device are you using to deliver O2? What is the temprature?
Click to expand...

Why would their tidal volume affect how long the O2 tank is going to last? The oxygen is delivered at a set rate, it isn't a demand valve. Same thing with the delivery device. A nasal cannula at 6lpm is going to use exactly as much oxygen as a SVN at 6lpm.
 
The tidal volume would affect the cylinder life if you're working with a demand valve type device. Use the equation as stated by n7lxi. Remember that different cylinder sizes have different constants and not all "D" are created equal (i.e. the Super D, which I believe is similar in size as an E).

Read the tags on the cylinders as it should tell you what the full volume is in litres. This is useful if you ever change cylinders for metal to the carbon fibre types, which hold a considerable amount more.

I also made up a chart that some find useful. I colour coded the various cells as the cylinder life approaches 30 minutes or less, with a residual of 200 psi.
 
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Aidey said:
Why would their tidal volume affect how long the O2 tank is going to last? The oxygen is delivered at a set rate, it isn't a demand valve. Same thing with the delivery device. A nasal cannula at 6lpm is going to use exactly as much oxygen as a SVN at 6lpm.
Click to expand...

There are many different devices that use oxygen including a demand valve. The OP didn't state that they were only using a NRB or NC.

After I posted I realized exactly what the OP was talking about and was going to post what n7lxi posted. Unfortunately I wasn't home to do so. Thats the last time I post when I'm tired.
 
Name a demand valve delivery device that is found on an ambulance that is not part of a nitronox system or ventilator.
 
Aidey said:
Name a demand valve delivery device that is found on an ambulance that is not part of a nitronox system or ventilator.
Click to expand...


An independent BiPAP is psuedoish demand valve due to the increased pressure on inspiration.
 
FROPVD? Oh wait, I forgot, we left the 70s behind.
 
Oh.. and OP... smart phone and the Clinicalc app. It's also useful for the pregnancy wheel app.
 
We don't need some weird ad hoc equation or an app; the ideal gas law should be good enough to estimate. Look at the cylinder label, which gives the capacity of the tank at full pressure (usually 2000 psi) and make some simple assumptions. Given constant volume, temperature, and ideal behavior, all reasonable assumptions, pressure and amount of oxygen remaining are directly proportional. For example, 1000 psi means half the capacity of the tank in liters delivered (actually in moles, but given our assumptions). From there, just divide by flow rate in L/minute.

To recap: find amount of oxygen (liters delivered) in full tank at filling pressure (on label), divide by current pressure/filling pressure to give current amount of oxygen, divide by liters/minute.

Looking at the "weird ad hoc equation" again, it appears to just slightly disguise the full volume of each tank size with a conversion factor in L/psi. Not really elegant or flexible.
 
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leoemt said:
There are many different devices that use oxygen including a demand valve. The OP didn't state that they were only using a NRB or NC.

After I posted I realized exactly what the OP was talking about and was going to post what n7lxi posted. Unfortunately I wasn't home to do so. Thats the last time I post when I'm tired.
Click to expand...

Like it's been point out, unless you're using a demand valve it's a fixed flow rate.

Using a vent would be a different formula but it's still not difficult to figure out how much time you have.

OP how much O2 do you carry and how long was this transport? We carry an onboard M cylinder, a D cylinder in our bag and 4 spare D cylinders. I've never even come close to running out of O2. Burned my whole M cylinder in a shift but still had plenty of O2 in the portables and the VSTs brought me a new onboard tank but that's not a luxury everyone has.
 
Aidey said:
I said found on an ambulance, not a museum. :P
Click to expand...

We still carry them...:sad:
The fire department likes them for rehab for whatever God forsaken reason
 
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