OSCAR Leak Rate Question

[AndyB]

I hope one of you experts out there can help me interpret OSCAR's Leak Rate data.

A little background, which I think is correct:

OSCAR shows whatever leak data a machine reports. In my case the data comes from a ResMed AirCurve 10 VAuto, which I understand reports as a leak only the portion of exhaust flow  that is "unintentional", meaning a leak that exceeds the designed intentional exhaust flow rate of the mask at a specified pressure. To determine the amount of an unintentional leak, ResMed programs its machines with expected amounts of  intentional exhaust flow rates for three types of masks (full face, nasal, and pillows). These three mask types will have different intentional exhaust flow rate curves for identical pressure levels. ResMed machines report as a leak only the excess of total exhaust flow over the intentional exhaust flow of the mask at the pressure used -- i.e., the net amount that is "unintentional."

Not all masks in each category have identical designed exhaust flow rate curves, however, so when ResMed's machines use a flow rate curve that it expects will be generally representative of the intentional exhaust flow rate for all masks in the specified category, it's often the case that the actual intentional exhaust flow of the mask used diverges from the flow rate curve used by the ResMed machine. Thus, the "unintentional" leak rate calculated by the ResMed machine --  and shown by OSCAR -- may be off by a large or small amount, depending on the difference between the exhaust rate ResMed used as the intentional rate and the actual intended exhaust flow rate of the particular mask being used.

For example, at 12 cmH2O a Brevida nasal pillows mask is designed to have an intentional exhaust flow rate of 39 LPM. However, if ResMed programs its machines to use an intentional exhaust rate for all nasal pillows masks of 35 LPM at 12 cmH2O, then anytime the actual exhaust flow rate exceeds 35 LPM at 12 cmH2O the machine will report a leak even though it's not really a leak unless the actual rate exceeds 39 LPM at 12 cmH2O. And vice versa if the programmed rate is higher than the mask's designed intentional flow rate.

So, finally, the questions:

-- How, when looking at OSCAR's leak rate chart, is one to know whether the leak rate shown by a ResMed machine is really an "unintentional" leak?

-- Or, does this really matter, and is the real issue what is the overall big picture of leaks shown and do the leaks appear to be adversely impacting the efficacy of therapy?

Pretty obtuse questions, I know. Nevertheless, any thoughts you experts may have would be very welcome.

AndyB

[rdw1982]

i am not an expert and may be corrected but you can set your leak rate in preferences    

[AndyB]

Yes, OSCAR lets the user set the large leak level (e.g., an "unintentional leak" greater than 24 LPM is usually considered a "large leak" by ResMed), but that doesn't address the question of how ResMed calculates the unintentional leak amount.

My question (quite far into the weeds, I admit) is whether it matters very much if there is a disparity between (1) ResMed's assumed exhaust flow rate curve for all masks in a certain category, and (2) the actual exhaust flow rate of the specific mask being used. Put another way, if a patient wears a mask with a designed exhaust flow rate at 12 cmH2O that is several liters per minute higher than the exhaust rate used by the ResMed machine at that pressure to calculate the unintentional leak amount (which is what the machine will report to OSCAR as the "leak rate"), the leak rate shown on OSCAR's chart will be higher than it should be since the mask was actually intended to exhaust more air than ResMed's machine is programmed to expect.

Maybe this horse doesn't deserve this beating, but I'm still curious whether the probable magnitude of this really matters. I think not . . . but . . .  .

[G. Szabo]

There is a wide leak range, either real or increased by this artificial issue, within which the instrument can compensate for the leak with an increased flow rate and deliver the treatment pressure intended. Hence, this issue you are describing will not influence the treatment in the overwhelming majority of cases. When the total leak is extreme, we advise our members to adjust their masks.

[AndyB]

That makes sense G. Szabo. Thank you . . . and it's gracious of you not to say "of course, dummy" at the end of your message

[Epark617]

Just wanted to say, new CPAP user here, I had the same question and I appreciate you asking it so eloquently and now I have an answer without having to spend an hour trying to put it to words!