Pressure in Auto Mode

[PaytonA]

Last night I switched from bilevel mode to auto mode on my Resmed S8 VPAP auto 25. Hoping to have less leakage when not running full tilt all of the time. My settings in bilevel mode are IPAP=20, EPAP=18. With these settings I have been getting a number of hypopneas and a few apneas every night.

I set the auto mode up as follows:
Min EPAP=16
Max IPAP=21
Pressure support=1.0

Here is what concerns me. My pressure chart was an absolute straight line at 17.0 with the same number of apneas and some more hypopneas. I realize that 17.0 is what is effectively the minimum IPAP of 17. I am guessing that the apneas may have been centrals but shouldn't the machine adjust pressure for hypopneas?

I am editing this because I was a little confused when I wrote it. I had originally thought that the pressure was 17.5 all night and could not understand why it did not change. When I re-reviewed it, I found that it was 17.0. So I just corrected what I had written without thinking about it. Obviously the machine thinks that I need a lower pressure. I am still confused about the hypopneas.

Best Regards,

PaytonA

[Peter_C]

Your post was me last NOV. After all *MY* dust has settled, I learned that I did not need my pressure so high, once I started controlling my leak rate better.

May I suggest a 2 week test? Open the machine up with the following settings in AUTO (remember, the machine cannot adjust your Pressure Support at all)

MIN EPAP 6.0
Pressure Support 6.0
MAX IPAP 25.0

This will effectively give you a base pressure of '12' on inhale, and '6' on exhale, but will allow the machine to raise it all it needs.

Then after 2 weeks (if you are willing to just watch data that long), you will learn what you really need as an average minimum. if you find that it stays at 12 all night lower the MIN EPAP by '1' for a week at a time, if you find that a lower EPAP is too uncomfortable, raise it the least possible, and lower the PS by the same number...

For instance, I need an EPAP of '7.0' for my comfort, period. So I started with a lower PS, and when the dust settled, I am currently at
MIN EPAP 7.0
PS 6.0
MAX IPAP 25.

Most nights it bounces between 13.2-14.0, but randomly every 3-9 nights it'll bounce to 18.6-21.0 for a short period. This is what 3 months of close data watching has taught me, and what is giving me a much lower AHI than I've had in years - and I am sleeping better too.

[robysue]

Last night I switched from bilevel mode to auto mode on my Resmed S8 VPAP auto 25. Hoping to have less leakage when not running full tilt all of the time. My settings in bilevel mode are IPAP=20, EPAP=18. With these settings I have been getting a number of hypopneas and a few apneas every night.

I set the auto mode up as follows:
Min EPAP=16
Max IPAP=21
Pressure support=1.0

Here is what concerns me. My pressure chart was an absolute straight line at 17.0 with the same number of apneas and some more hypopneas. I realize that 17.0 is what is effectively the minimum IPAP of 17. I am guessing that the apneas may have been centrals but shouldn't the machine adjust pressure for hypopneas?

The Auto algorithm does NOT increase the pressure every time there is a H or an OA. Typically for the machine to increase the pressure there need to be two events within about 5 minutes of each other. Isolated events don't result in pressure increases. (This mimics the titration guidelines put out by the AASM.)

Also, on some machines that cannot distinguish between OAs and CAs, the manufacturer has the machine not respond to any apneas when the pressure is above 10 cm in case those apneas are central in nature and a pressure increase might trigger the user going into an overshoot/undershoot cycle when it comes to blowing of CO2, which can then trigger a clinically significant number of central apneas.

I am editing this because I was a little confused when I wrote it. I had originally thought that the pressure was 17.5 all night and could not understand why it did not change. When I re-reviewed it, I found that it was 17.0. So I just corrected what I had written without thinking about it. Obviously the machine thinks that I need a lower pressure. I am still confused about the hypopneas.

You need to find out more about the particular auto algorithm used by the Resmed S8. It may be the case that it simply is programmed to NOT respond to apneas when the EPAP is over 10cm.

[PaytonA]

Last night I switched from bilevel mode to auto mode on my Resmed S8 VPAP auto 25. Hoping to have less leakage when not running full tilt all of the time. My settings in bilevel mode are IPAP=20, EPAP=18. With these settings I have been getting a number of hypopneas and a few apneas every night.

I set the auto mode up as follows:
Min EPAP=16
Max IPAP=21
Pressure support=1.0

Here is what concerns me. My pressure chart was an absolute straight line at 17.0 with the same number of apneas and some more hypopneas. I realize that 17.0 is what is effectively the minimum IPAP of 17. I am guessing that the apneas may have been centrals but shouldn't the machine adjust pressure for hypopneas?

The Auto algorithm does NOT increase the pressure every time there is a H or an OA. Typically for the machine to increase the pressure there need to be two events within about 5 minutes of each other. Isolated events don't result in pressure increases. (This mimics the titration guidelines put out by the AASM.)

Also, on some machines that cannot distinguish between OAs and CAs, the manufacturer has the machine not respond to any apneas when the pressure is above 10 cm in case those apneas are central in nature and a pressure increase might trigger the user going into an overshoot/undershoot cycle when it comes to blowing of CO2, which can then trigger a clinically significant number of central apneas.

I am editing this because I was a little confused when I wrote it. I had originally thought that the pressure was 17.5 all night and could not understand why it did not change. When I re-reviewed it, I found that it was 17.0. So I just corrected what I had written without thinking about it. Obviously the machine thinks that I need a lower pressure. I am still confused about the hypopneas.

You need to find out more about the particular auto algorithm used by the Resmed S8. It may be the case that it simply is programmed to NOT respond to apneas when the EPAP is over 10cm.

Actually, I had at least one incident where I had 5 hypopneas within 6 minutes. I will include the graph. For the night in question I had an AI of 0.6 and an HI of 12.3. The following night with the same settings in the machine, I had an AI of 0.0 and an HI of 10.9.

I am still working on my leakage rate but my new FFM has gotten it down to a much more acceptable level. Most of the night in question was within the 24.0 l/m acceptable rate.

Best regards,

PaytonA

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[robysue]

PaytonA,

I don't know that much about the S8 Auto algorithm. But it may be worth asking your sleep doc about when the S8 VPAP is supposed to increase pressure when EPAP > 10cm.

The S8's are suspected of being pretty aggressive in scoring Hs and maybe that is why it is less aggressive at responding to them?

[Peter_C]

Also, on some machines that cannot distinguish between OAs and CAs, the manufacturer has the machine not respond to any apneas when the pressure is above 10 cm in case those apneas are central in nature and a pressure increase might trigger the user going into an overshoot/undershoot cycle when it comes to blowing of CO2, which can then trigger a clinically significant number of central apneas.

Just an FYI - As I have the same machine, and have used it for years, I *can* say, that even with pressure +10, it will raise it higher in auto mode.

This machine cannot 'see' CAs at all to be true,but it's only other limitation is not having the ability to self-adjust the Pressure Support. That's why it is suggested to first test without making constant changes to the PS, but rather leave it at a set level, then see how it goes. Most seem to suggest a PS of 4 to 6 only (which personally I do not understand) - A CPAP with an EPR of 3 is just like a bilevel with a PS of 3 if you think about it.

[Dgsr]

Most seem to suggest a PS of 4 to 6 only (which personally I do not understand) - A CPAP with an EPR of 3 is just like a bilevel with a PS of 3 if you think about it.

Hi Peter,

I've often wondered that myself. I've read that higher PS can cause issues with some people (induce centrals, hyperventilation, etc.).

But didn't understand why you would bother to prescribe a bipap for a PS of 3 when technology like EPR exists.

Hi Robysue,

I don't know much about the algorithms, but I can see my S9 VPAP adjusting pressure throughout the night, sometimes in spots where there was an apnea, sometimes in spots there was no apnea. I think there's more to it than just adjustment after multiple apneas. Either that, or I'm misreading my charts.

[PaytonA]

Most seem to suggest a PS of 4 to 6 only (which personally I do not understand) - A CPAP with an EPR of 3 is just like a bilevel with a PS of 3 if you think about it.

Hi Peter,

I've often wondered that myself. I've read that higher PS can cause issues with some people (induce centrals, hyperventilation, etc.).

But didn't understand why you would bother to prescribe a bipap for a PS of 3 when technology like EPR exists.

Hi Robysue,

I don't know much about the algorithms, but I can see my S9 VPAP adjusting pressure throughout the night, sometimes in spots where there was an apnea, sometimes in spots there was no apnea. I think there's more to it than just adjustment after multiple apneas. Either that, or I'm misreading my charts.

Peter,

I think that I remember reading in a response on this board ( I think it might have been from Robysue) that the algorithm for detecting the initiation of inhalation and exhalation is better on the bilevel machines.

Dgsr,

Again, if I remember correctly, the auto machines look for a precursor to the apnea to adjust the pressure and possibly sometimes or if it is a central maybe that precursor does not exist or is too ephemeral.

Best Regards,

PaytonA

[me50]

"Also, on some machines that cannot distinguish between OAs and CAs, the manufacturer has the machine not respond to any apneas when the pressure is above 10 cm"

Robysue, can you explain this a little more, especially the part about pressure above 10 cm?

Thanks.

[zonk]

"Also, on some machines that cannot distinguish between OAs and CAs, the manufacturer has the machine not respond to any apneas when the pressure is above 10 cm"

Robysue, can you explain this a little more, especially the part about pressure above 10 cm?

Thanks.

From ResMedical "interview with Dr.Michael Berthon-Jones" (this interview some time ago before S9 AutoSet central apnea detection)
http://www.resmed.com/au/assets/document...0906r1.pdf

Why doesn’t ResMed's AutoSet respond to apnea above 10 cmH2O in pressure?
I mentioned before that the higher the pressure, the more central hypopneas you will have. At a pressure somewhere around 10 cmH2O, the central hypopneas become central apneas. On the other hand, the vast majority of obstructive apneas are already well controlled by 10 cmH2O, and we are only fine tuning using snoring and flattening. So it is a pretty good bet that if the pressure is already above 10 cmH2O, any apneas are most likely central, and you should leave them alone (except in patients with central apneas due to heart failure). But if the pressure is below 10 cmH2O, most apneas will be obstructive and you should put the pressure up. There’s nothing magical about 10 cmH2O, it’s just a good place to put the line in the sand.