The APAP Road Less Traveled
A sleep physician discusses several aspects of auto-adjusting CPAP not often considered.
By Edward D. Michaelson, MD FACP FCCP FAASM
Auto-adjusting CPAP (ACPAP or APAP) for the treatment of obstructive sleep apnea (OSA) is increasing in part due to perceived advantages and improving technology but also driven by cost considerations, payor policies, and the home sleep test (HST) direct to APAP model. The survey results in the March 2015 issue of Sleep Review (SR) document the increasing market penetration of HST. Although the survey showed a slight decrease in APAP use, I suspect this is lag-time related and that the use of APAP will continue to increase.
Many studies have documented the benefits and effectiveness of APAP as compared to CPAP based on attended titration. It is the purpose of this article to address other issues related to APAP but that are not often considered.
A Little History
In 2002, the American Academy of Sleep Medicine published practice parameters with recommendations regarding the use of APAP devices for titrating pressures and treating adult patients with OSA (SLEEP, Vol. 25, No. 2, 2002), which were updated in 2007-2008 (SLEEP, Vol. 31, No. 1, 2008). The October 2008 issue of SR (“APAP in the Age of Home Testing”) outlined these practice parameters as related to cost and efficiency, a possible billing code for APAP, and made some predictions about market share.
An article entitled “Auto-adjusting Positive Airway Pressure Treatment for Sleep Apnea Diagnosed by Home Sleep Testing” (Journal of Clinical Sleep Medicine, Vol. 10, No. 12, 2014) by Berry and Sriram reviewed the current literature and concluded that, after diagnosis of OSA by HST, treatment with APAP results in equivalent PAP adherence and improvement in sleepiness compared to a PSG titration with CPAP treatment. In the same issue, a commentary by Batool-Anwar and Quan discussed some limitations of the studies reviewed but also acknowledged their importance. Their commentary also emphasized that Berry and Sriram made an important contribution providing further validation for the use of APAP without an in-laboratory PAP titration in certain patients diagnosed with OSA using a HST and that future studies are needed to determine whether this paradigm will be applicable to the “real world.”
The recent article by Auckley in the April 2015 issue of SR (“Can We Assure Adherence in Patients Titrated by Autoadjusting CPAP at Home?”) reviews methods shown to improve CPAP adherence, compares initiating APAP to in-lab titrations, and suggests how a combined approach using both technological and behavioral interventions can improve adherence to CPAP therapy and help ensure success for patients. The article also emphasizes the importance of correct patient selection, the use of a standardized protocol for patient education, instructions prior to initiation of home APAP, and close clinical follow-up.
Interpret with Caution
The results of studies that evaluate the effects of APAP must be interpreted with caution as the methods used for identification of respiratory events, how those events are defined, and the proprietary algorithms that govern the auto-adjustment of pressure vary among APAP manufacturers and may impact the results, conclusions, and comparisons of APAP studies to the extent that different devices are used both among patients and among studies.
It is important for providers to understand that not only are the algorithms for adjusting pressure different, but the methods of pressure and flow detection vary as well. These differences may be amplified by the frequency, magnitude, and pattern of respiratory events that occur in a specific patient (and night to night variability as well) and can also affect patient comfort and acceptance. Variables among APAP devices include:
How the device responds to snoring, flow limitations, clusters of obstructive and/or central apneas and/or hypopneas; what situations will trigger increasing the pressure; and how, when, and at what rate (slope) and what increments of magnitude will machines increase, sustain, and then lower the pressure back down and to what level.
How the machine determines the patency of the airway; to what degree flow must be reduced to determine whether a given event is a central or obstructive apnea or a hypopnea; and how is that hypopnea different than one determined by conventional sleep testing (which by definition includes a degree of O2 desaturation).
Each algorithm has its own strengths and weaknesses in terms of therapy effectiveness, possible effect on and compensation for mask leak, and comfort for different patterns of OSA among patients. There are many commercially available APAP devices, and some sleep physicians—and to a greater extent other providers—may not know specifics of the performance differences. Should manufacturers disclose this information? Should the algorithms be adjustable for specific patients by knowledgeable providers?
In the September 2009 issue of SR (“Auto-Adjusting Positive Airway Pressure”), McCoy, Diesem, and Eiken described a bench comparison of five APAP devices for response to apnea, hypopnea, and flow limitation, identified performance variables, and challenged clinicians to understand the issues surrounding APAP therapy with regard to product capabilities and the science behind them.
The general consensus was that all APAP devices are capable of providing positive results. Unfortunately, there are no standards established for the “appropriate” pressure response to a specific breathing pattern and in most situations the considerations for choosing a device are features, price, and payor policies.
As the result of the bench tests, the authors and SR asked the manufacturers to address the following (paraphrased) issues regarding their approaches to algorithm design: Please generally summarize the approach used in your APAP machine’s algorithm to detect sleep-disordered breathing events. How does your product respond once a sleep-disordered breathing event is detected? What was the basis or reference for incorporating your described approach?
The details of the bench tests and the vendors’ responses to these questions are provided in the article.
The HST to APAP Model
In the November 2014 (“Sleep Apnea and Trucking: Where Are We Now?”) and January 2015 issues of SR (“Should, Would, or Could Providers Do Home Sleep Testing?”), I addressed various aspects of HST and the HST to APAP model. I outlined a suggested decision tree for screening, analyzing, and acting on the results of the HST and criteria for when APAP is (or is not) appropriate. In short, if the decision to begin APAP is based on HST, the initial pressure range could be 4-20, but it may be better to set the minimum pressure somewhat higher depending on the severity of the OSA and O2 desaturations. Either way, periodic data downloads from the APAP unit should be reviewed for adherence, respiratory events, and leak, and the pressures adjusted based mainly on the frequency of respiratory events with an attempt to narrow the range leaving a little extra room at the top for nights when more REM, and/or supine sleep, and/or alcohol or medication consumption may occur.
Furthermore, if APAP, or for that matter an oral appliance (OA), is started based on the HST and if the HST shows “significant” O2 desaturation, then once the APAP or OA is appropriately adjusted, an overnight oximetry should be considered to assure correction of SpO2. Ultimately, outcomes are what really count so if symptoms do not improve or worsen after a reasonable trial of (APAP or OA) therapy, an attended titration and/or consultation with a sleep specialist should be considered. The same recommendations should apply to fixed CPAP based on an attended titration.
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