PB420E Max Pressure for Command on Apnea: 10?

alsarnac · Post by **alsarnac** » Mon Sep 10, 2007 4:45 am

After over a year of autpap use at 9cmH2O min and 14cmH2Omax with my PB420E, my data indicate that my pressure efficient more than 90% of time is 11. Out of curiosity, I've decided just these past 7 days to shift to straight CPAP at 11cmH2O, and to my surprise my AHI is much lower. I'm toying with the idea of shifting back again to autopap but this time with 11cmH2O min and 14cmH2O max and make comparative analysis of the data. My only concern though is do I have to adjust the max pressure for command on apnea which is on manufacturer's default at 10cm in my unit if I proceed with my experimentation (given that I'll make an attempt this time to use 11cm min.)? I'd appreciate all your help or suggestions. Thanks.

ozij · Post by **ozij** » Mon Sep 10, 2007 7:44 am

That's a good question.

Suppose you put your bottom pressure at 11, and you your top pressure at 11 too, and don't touch the maximum pressure for command on apnea. Would that mean the pressure will go down to 10 when you have an apnea???

If you feel well after a week on 11, then yes, you'll have to chage that parameter in order to get the comparison you want.

O.

tillymarigold · Post by **tillymarigold** » Mon Sep 10, 2007 8:43 am

I believe "max pressure for command on apneas" is not the max pressure the machine goes to, but the most it will raise the pressure at one time. It does this in case you have a central instead of obstructive apnea although I don't quite understand the medical reason that it's necessary.

So like if you had a range of 6-20 and it was at 6 and you had an apnea, the "max pressure command on apnea" setting of 10 would mean it would only raise the pressure to 16 for that apnea, not all the way up to 20. Whereas if the machine was already up at 12 and you had an apnea, the highest the machine would go would be 20 since that's the top of the range.

I have my "max pressure for command on apnea" set at 10 and my range is 8-12, and I've certainly had it go up to 11. So a setting of 10 definitely doesn't mean it can't go higher than 10.

ozij · Post by **ozij** » Mon Sep 10, 2007 9:07 am

If a machine is on auto it has to know how to behave when it discovers an apnea. Furthermore, it has to know how to react to a non-obstructive apnea.

When a machine is not on auto, the assumption is that during the titration study the higher pressure was found beneficial, and that during the titration the beneficial pressure did not cause pressure induced apneas.

On auto:
Resmed machines simply never raise the pressure higher than 10 in response to an apnea.

Respironics machines nudge the pressure up gently, and if the apnea doesn't resolve within 3 nudges, they will stop going up, and maybe (I don't remember) lower the pressure gently. This is regardless of the pressure they are at.

Puritan Bennett machines can let you define a "maximum pressure for apnea" that may be lower than your maximum pressure, and capped wherever the sleep study indicates it should be. They also let you define a maximum pressure in response to apneas which is higher than 10.
And they are very good a detecting central apneas. They don't detect all of them, which is why fiddling with that command is not recommended - but those the identify are central (non-obstructive) for sure.

Anyone on straight cpap has all his/her apneas treated by that straight cpap pressure - like I said, that's based on the assumption that the patient's sleep was viewed by a technician who found out the best level for having the least number of apneas - a level which by definition keeps the airways from obstructing, and avoids pressure induced apneas as well.

O.

Snoredog · Post by **Snoredog** » Mon Sep 10, 2007 10:53 am

Command on Apnea = 10.0 by default. What that parameter says is the machine won't respond to an stand-alone apnea above 10.0 cm pressure for fear it may be a central apnea.

It can be compared to the A-10 algorithm function found on the Resmed AutoSet, difference being the 420's is adjustable vs. hard coded and it uses additional rules for it to apply since the machine has the ability and listens for cardiac oscillations.

Above that threshold the machine would have to see the apnea associated with a FL or hypopnea before any response from the machine would be seen.

It is important to understand below that parameter the machine will respond to stand alone apnea seen, this means it can theoretically confuse that apnea for CA since only about 60% of CA have an associated open airway. If you have those showing up on the reports you can experiment by lowering or raising that parameter where it will impose different rules for response.

My threshold was 9.0 cm, so I lowered that parameter to 9.0 and seen a much better response and improved AHI. Alternately, you can increase that parameter if needed higher than default 10.0 cm. The 420e is a very flexible machine.

rested gal · Post by **rested gal** » Mon Sep 10, 2007 7:19 pm

Most people should leave the PB 420E's advanced setting, "Max pressure for Command on Apnea" right where it is set by the manufacturer...on 10 cm H2O.

alsarnac wrote:do I have to adjust the max pressure for command on apnea which is on manufacturer's default at 10cm in my unit if I proceed with my experimentation (given that I'll make an attempt this time to use 11cm min.)?

I just now set my 420E to the pressures you plan to use -- 11 Min, 14 Max. I also set the starting pressure at 11, and no ramp. When I went farther along in the clinical menu and got to one of the last items that said "A" (and a pressure) in the window, that was set at 11. I figured that was probably the "Command on Apnea" setting and I tried to set it down to 10. Would not budge down off 11, presumably because my minimum was now set for 11.

If I'm right about the "A" setting in the window being the advanced setting for Command on Apnea (I'm too lazy to look it up in the Provider manual ) that means the setting will automatically move up to whatever your minimum is, if you've set your minimum above 10.

Tried something else just now... I reset the machine to 10 Min, 20 Max, starting pressure 10, no ramp. This time when I got to the "A" setting, it was still on 11, so if that's the Command on Apnea setting, it doesn't automatically drop back down to 10 when the minimum pressure setting is changed from above 10 back down to 10 or less. You might want to keep that in mind if you ever move your minimum setting back down off 11 and want to again use the default of 10 for the "Max pressure for Command on Apnea."

alsarnac · Post by **alsarnac** » Mon Sep 10, 2007 10:35 pm

Learning indeed is a continuing process. Right you are, rested gal, the setting will automatically move up to whatever your minimum is if the minimum is set above 10. Now I can proceed with my experimentation . . . A million thanks to you all folks.