(06-09-2014, 03:14 PM)jcarerra Wrote: I just went to my Primary Care doc's office today and picked up the sleep study and titration study reports. The latter says, " The patient will benefit from CPAP at 12cm...with heated humidifier."Bummer about the doc not willing to advocate for an APAP.
I absolutely believe I need autoset--to get enough pressure during the clusters...and don't really understand the logic for anybody that says you need XXXX cm during events, so we will give it to you all night! huh? How is that sensible!
However, I do want to try to explain the logic behind the preference many doctors have for prescribing CPAP rather than APAP. It's important to understand that not all of the reasons that docs prefer prescribing CPAP to APAP boil down to some version of "super inflated ego" or "ignorant incompetence". Some of their logic does make sense to me, and some, quite frankly, does not. Regardless, here are some of the reasons that docs tend to prescribe CPAP at n cm rather than APAP with a range:
Many docs are simply not very aware of the wide choices in equipment that are out there.
This is particularly true of primary care physicians. They know CPAPs exist, but they really don't know that much about them. And hence they take the lab's recommendation and they write the script in the obvious way. Keep in mind that the average PCP has received very little formal training in sleep medicine, let alone CPAP management. And unless a very large number of his/her patients are relying on the PCP for CPAP follow up, a typical PCP has little reason to learn very much about CPAP therapy and is likely to simply defer to the specialist who wrote the sleep study summary.
Many of the docs who ARE knowledgeable about APAPs don't trust the APAP algorithms all that much--Part I.
Many of these docs are sleep docs. Why they distrust the APAP algorithms is a complex issue and it's not all about over-blown egos. Sometimes the distrust is long standing---the early Auto algorithms really did have some pretty severe problems and limitations.
There's a discussion on another board right now about the limitations of the S9 Escape Auto's auto algorithm vis a vis the newer S9 AutoSet's Auto algorithm. The Escape Auto's auto algorithm is the old S8 AutoSet's auto algorithm, and among other things, that particular algorithm will NOT increase the pressure in response to any cluster of apneas and hypopneas that occur when the pressure setting is AT or ABOVE 10 cm. The older auto algorithm was designed with this limitation in order to prevent inappropriate pressure increases in the small number of OSA patients who develop problems with pressure induced centrals.
So historically speaking, the Auto algorithms have a mixed record in terms of providing appropriate pressure responses when clusters of apneas and hypopneas are detected.
Many of the docs who ARE knowledgeable about APAPs don't trust the APAP algorithms all that much--Part II.
The newer Auto algorithms by Resmed and PR claim to distinguish between central and obstructive apneas and respond appropriately. But both companies are not very forth coming with the particulars of the algorithms (they are proprietary after all) and much of the data to back up the claims that the machines work as promised were done by the companies in company labs OR done with moneys coming from the companies. Independently bench testing the algorithms is not easy, and the handful of studies that I've been able to locate do point out that the different auto algorithms respond in very different ways. And it's not at all clear how a doctor should use those differences to choose an APAP that is most likely to work for a particular patient.
At the root of the distrust of the Auto algorithms ability to correctly respond to sleep disturbed breathing events is a mistrust of the machine's ability to accurately record efficacy data in the first place. There's a general consensus that the efficacy data is useful as trending data---the long term summary data is seen as having real value in the clinical setting for identifying which patients are still having real problems with under treated OSA after several weeks or months on PAP therapy. And that allows the doc to then consider what things might be contributing to the long term clinical reasons the person is not responding as expected to PAP therapy.
But on a breath-by-breath analysis basis, the sleep docs tend to remain on the skeptical side of trusting the detailed data that the APAP uses to determine when to raise the pressure and how much to raise the pressure by.
Many of these docs will trust the leak data---it's easy to establish how that data is gathered and what it means. But the AHI data? Again, each company that makes a full efficacy data machine has their own proprietary algorithms for scoring the events. And those scoring criteria are NOT readily available, but they do indeed matter when it comes to interpreting the data recorded.
Apneas are pretty easy to score: The flow rate into the lungs drops below 10% of the "running baseline" for at least 10 seconds is the usual definition. But how is the "running baseline" computed? And how much does that matter? Turns out, it varies a lot from company to company and it DOES affect the scoring of some "apneas".
The definition of hypopnea varies even more from company to company. Some companies choose "airflow is below 50% of the running baseline" and others choose "airflow is below 60% (or 70%) of the running baseline". When Resmed redid their hypopnea detection algorithm between the S8 series and the S9 series, they apparently reduced the sensitivity of the machine to score Hs by changing the criteria for scoring a hyponpena. A lot of people (both patients and docs) suspected the S8 was (possibly drastically) over scoring Hs; there are now some people who fret about whether the S9's underscore Hs.
Classifying the apneas as central or obstructive is even more controversial. The companies that claim their efficacy data machines can do so use proprietary algorithms, and hence there is limited information about how those algorithms are designed available to people not employed by the companies. What is known about the algorithms is that they typically are trying to distinguish between OAs and CAs based on the patency of the airway. The problem with is that in a lab, a central apnea can be scored even if the airway is blocked. Effort to breath is the critical piece of data for distinguishing a central apnea from an obstructive apnea in the lab. And it is known that in a certain number of people, the airway can and does collapse after the start of the central apnea. And this kind of central apnea can easily be mis-scored as an OA (and trigger an inappropriate pressure increase) by the existing central apnea detection algorithms.
And since PAP machines have no EEG, there is no way (beyond patient self report) to know whether a patient was awake or asleep when any particular event or cluster of events occurred. It's particularly difficult to tease out "sleep-wake-junk" (SWJ) breathing from the efficacy data. SWJ is when a person is dozing in and out of sleep and so some of the breathing is sleep transitional breathing and some is wake breathing. Both sleep transition breathing and wake breathing are regularly (and incorrectly) scored as CAs, OAs, and Hs by today's top of the line efficacy data machines. And when an APAP inappropriately raises the pressure during SWJ, that can make it harder for the patient to establish sound sleep with a regular, even sleep breathing pattern.
In short: The limitations on the accuracy of the breath-by-breath data can lead an APAP to respond inappropriately under some not uncommon circumstances. For many patients, this inappropriate response is not likely to do any real damage. But for a small group of patients, the inappropriate responses by their home APAP may contribute pretty significantly to poor efficacy results and/or serious adjustment problems.
Editorial note: While I think the problems with the accuracy of the data are real AND that in some cases inappropriate response to clusters of mis-classified or mis-scored events do cause serious problems, I think the answer is switching an APAP into straight CPAP mode rather than simply refusing to allow the patient to have (and try) and APAP running in Auto mode.
Well constructed double blind studies have repeatedly shown that starting people out on APAP instead of CPAP does NOT increase overall compliance rates or the effectiveness of therapy.
It is true that many (not all) of these studies use the default 4-20cm range for the APAPs, and that may very well put the APAPs at a disadvantage. But, if you read the advertising aimed at docs and dmes at the time APAPs were first being developed, the manufacturers were pushing the idea that leaving the APAP range wide open for the long term settings was a reasonable idea.
Still the fact remains: The manufacturers have tried to sell the idea of increased compliance with APAPs to the DMEs and sleep docs, but the scientific data indicates no statistical difference in compliance between newbies set up with CPAPs vs. APAPs.
Editorial Note: Quality scientific studies have shown that quality patient education and support, including close follow up from both the DME and doc during the first three months does significantly increase long term compliance. Studies have shown that docs and DMEs that are proactive in addressing common newbie problems have much better patient compliance than docs and DMEs who simply tell the newbie to contact them if the newbie runs into any problems.
Anecdotal evidence indicates that some people's sleep is deeply disturbed by the constantly changing pressures of a APAP in auto range.
There really are folks who sleep more soundly in CPAP mode than in Auto mode. And for a newbie, there's enough other stuff to get used to, so why add into that potent mix, the potential that changing pressures all night long will prove to be very disturbing to the new PAPer's sleep?
Editorial comment: Since APAPs can be set to CPAP mode, I personally do NOT think this is a reason to start people off with a straight CPAP machine rather than an APAP machine. If I had my way, people would start with an APAP set to CPAP mode and be switched to APAP either at the patient's request or when the patient starts having difficulties.
In conclusion, it's not merely a matter of some combination of inflated egos, laziness, incompetence, or ignorance that leads some sleep docs to strongly prefer prescribing CPAP at 12 cm over APAP at 9-14 cm.
But the thing is, setting a patient up with an APAP running in CPAP mode gives you more flexibility should things change in the future or should the patient run into problems. Smart DMEs know this and simply sell the patient an APAP set to CPAP mode when the patient comes in with a script that says CPAP at 12 cm. If the patient starts having problems and the doc decides to do a temporary auto-titration for a week or too to get some evidence in support of what an appropriate pressure might be, the DME doesn't have to set up a loaner machine, which they then have to take back and sterilize for the next person they lend it to. All the DME has to do is change the person's settings on his/her machine and send the patient on their way. And there's no more dealing with paperwork to explain a two week hole in the compliance data when talking to the insurance company.
In other words, the DMEs are as much (or more) to blame than the docs are when it comes to setting patients up with CPAPs instead of APAPs.