Strange Flow limitations

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Postby JHawks93 » Wed Sep 28, 2011 8:13 pm

For the DME then you're writing a script for 10 cmH2O. I just think it would be terribly confusing to state that 8cmH2O at the mask was successful in eliminating obstructive events and snoring, but that the machine needs to be set at 10 cmH2O. That's all I'm saying.
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Postby bduce » Thu Sep 29, 2011 10:51 am

Jhawks
At the end of the study we measure the recommended pressure with a regularly calibrated manometer. The pressure read at the manometer is the pressure we put on the script.

The mask pressure calibration on the polysomnogram may not be correct, same goes for what the machine thinks it is putting out.
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Postby JHawks93 » Thu Sep 29, 2011 11:08 pm

Where is your manometry reading taken? Are you taking the reading at the mask or more proximal to the CPAP?
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Postby bduce » Fri Sep 30, 2011 12:26 am

We leave the tubing attached and take it from the end of the tubing. All machines we set up for patients are based on the calibrated manometers. I have personally seen some machines, as they get older, have their internal calibrations change. For example, I need to set a machine to 12.8cm to get a pressure reading of 12cm. At a machine setting of 12cm I got 11.2cm. I find that the linearity is still good just the baseline sometimes changes.

The digital manometer is calibrated by our biomedical technicians once a year and we also perform spot checks monthly using our own U-tube fluid manometers.

The one thing I would deifnitely do is to look at your equipment specifications JHawk. Too often we look at the signal and say "we have an error" when we may not have one. For example - I get my staff saying to me "the pressure manometer needs recalibrating as it is out 0.4cm". But if you look at the design specifications for most of the pressure manometers we use they have a design accuracy of + or - 1cm! So technically anything within that range is still within specification and can be attributed to natural variation of the measurement system.

Too many people are expecting accuracy within of 0.1-0.2cm in these manometers when the ones we are using are not actually designed for that level of accuracy.

Putting it out there for all you folks
Take the time to learn the details of what your equipment can and can't do. Not just for your own sake but for the sake of the profession. Many physicians are pretty good with the overall rules etc but it is the nuances associated with the measurement and scoring is what should set us apart from them.

I know some of you have been saying that many of us will be replaced by automation but that is only going to come if we do demonstrate to physicians and medical directors the importance of our knowledge and experience and how it contributes to positive patient outcomes.
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Postby JHawks93 » Fri Sep 30, 2011 12:43 pm

Appreciate the feedback and am glad to see that someone else is using a water column manometer too. As I just posted in a different thread - I find that the digital manometers become unstable as the internal batteries begin to fade. Just because it "turns on" doesn't mean that it's accurate. I would be nervous with only checking the device once a year, but it sounds like you're performing a more rigorous QC with it than that.
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Postby JHawks93 » Fri Sep 30, 2011 12:49 pm

Forgot to comment....

We also have a DME arm of our company and I too find that some older CPAP machines need fine calibration to provide the actual prescribed pressure. Too often, however, the pressure measured my manometer is off because the patient accidentally changed the altitude setting in the menu!

As a rule of thumb, however, we measure each CPAP unit at setup by manometer. The internal software setting is generally reliable in ensuring the correct CPAP pressure at outlet, but there are those rare occasions that it is off slightly.
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Re: Strange Flow limitations

Postby Onesight1 » Mon Jan 09, 2012 11:16 am

LadyCandy wrote:No snoring was heard or seen in the snore channel. What in the world is going on with the flow effort in this CPAP study?

Image


I use Alice 5 at my lab , and I almost want to say that the strange morphology of the flow signal is usually noticed when I use FLEX technology.
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