What Lies Ahead for Portable Monitoring of Obstructive Sleep Apnea?

PHILADELPHIA—Widespread use of portable monitors and autotitrators for at-home assessment and treatment of obstructive sleep apnea (OSA) is inevitable and may prove to be an efficient patient management strategy, said Samuel T. Kuna, MD, at the American College of Chest Physicians’ 2008 Annual International Scientific Assembly. Yet despite last year’s decision by the Centers for Medicare and Medicaid Services (CMS) to provide coverage for continuous positive airway pressure (CPAP) therapy if the diagnosis is made via home monitoring, he acknowledged that much more research—and standardization—is needed in this area. (Note: In March of this year, CMS decided to expand their coverage to include portable monitoring itself.)

“We don’t have the evidence to support how we should be using portable monitors and which patients should be tested in this manner,” stated Dr. Kuna, Associate Professor of Medicine at the University of Pennsylvania and Chief of the Pulmonary, Critical Care, and Sleep Section at the Philadelphia Veterans Affairs Medical Center. In addition, there is great variability among the different devices. With this in mind, he advised clinicians to become very familiar with the operating characteristics of the monitor used at their laboratory, rather than try to gain extensive knowledge of them all.

LABORATORY POLYSOMNOGRAPHY VERSUS PORTABLE MONITORING

Four types of sleep studies can be used for the diagnosis of OSA, Dr. Kuna pointed out, although the distinctions between the classifications may change with advances in technology. A type I test is a full polysomnography with at least seven channels—including signals that assess sleep stage—that is attended by a technician in a sleep clinic. For the most part, this has been the gold standard against which researchers try to validate portable, unattended monitoring with type II, III, and IV devices, said Dr. Kuna. Type II monitoring records the same channels as a type I test. Type III devices do not record sleep staging, and while some type IV devices record as few as one variable, the CMS requires the use of at least three channels for type IV tests.

Until recently, the typical protocol for portable monitor validation studies was to perform them over two nights in a randomized, crossover fashion—with patients variously undergoing in-laboratory polysomnography with simultaneous portable monitor recording one night, and at-home portable monitoring on another night.

“This type of study design is doomed to failure,” asserted Dr. Kuna. “We’re trying to compare apples and oranges.”

First, type III and IV machines do not include sleep staging information, he remarked; therefore, when the apnea-hypopnea index (AHI) is calculated, the number of events is divided by the amount of time recorded—whether the patient is asleep or not. In-laboratory polysomnography and type II devices divide the number of events only by the amount of time the patient is asleep, yielding a higher, more accurate AHI.

Second, even with in-laboratory polysomnography, there is a lot of night-to-night variability in the severity of disordered breathing. “In many cases, diagnosis of OSA depends on which night you test the patient,” said Dr. Kuna. To account for these inconsistencies, he suggested that researchers who seek to validate portable monitors against polysomnography based on AHI should perform two nights of in-laboratory testing and two nights of home testing. “This methodology will then allow you to factor out variability in AHI from one night to another in your analysis,” he added.

AT-HOME TITRATION

Recently, some researchers have taken another approach to validating portable monitors; namely, evaluation of entire disease management pathways. One of two studies that have used that design was conducted by Mulgrew et al. Patients referred to a sleep clinic were confirmed to have OSA and were randomized to standard in-laboratory polysomnography, or ambulatory autotitration CPAP (auto-CPAP) and overnight oximetry. Follow-up polysomnography at three months confirmed that there were no significant differences in the AHI on CPAP, Epworth sleepiness scale score, or quality of life measures. In fact, some of the patients who received the gold standard in-laboratory polysomnography were inadequately titrated and CPAP adherence was significantly better in the at-home, autotitration group.

In a six-week study by Berry et al with a similar design, nightly adherence to CPAP, decrease in Epworth sleepiness scale score, and improvement in global Functional Outcome of Sleep Questionnaire score did not differ between patients who received portable monitor testing and auto-CPAP and patients who received in-laboratory assessment and CPAP titration. It is important to note, however, that there is very little data regarding the safety of these machines for patients with comorbidities, particularly congestive heart failure or COPD, cautioned Dr. Kuna.

A PARADIGM SHIFT

Dr. Kuna contended that the CMS’ decision regarding portable monitoring is going to lead to a paradigm shift in how OSA patients are managed. “It is very likely over time that as increasing evidence appears, insurance companies will follow suit and accept, perhaps even demand, portable OSA monitoring,” he said.

Dr. Kuna reported that he is in the process of recruiting patients for his own Veterans Affairs–funded sleep research study comparing in-laboratory versus ambulatory management of patients with OSA. In addition to examining CPAP adherence and functional outcome in the two groups, “This will be the first prospective, randomized controlled study looking at the cost effectiveness of portable monitor testing,” he said.

—Jessica Dziedzic

Suggested Reading
Berry RB, Hill G, Thompson L, McLaurin V. Portable monitoring and autotitration versus polysomnography for the diagnosis and treatment of sleep apnea. Sleep. 2008;31(10):1423-1431.
Collop NA, Anderson WM, Boehlecke B, et al. Clinical guidelines for the use of unattended portable monitors in the diagnosis of obstructive sleep apnea in adult patients. J Clin Sleep Med. 2007;3(7):737-747.
Mulgrew AT, Fox N, Ayas NT, Ryan CF. Diagnosis and initial management of obstructive sleep apnea without polysomnography: a randomized validation study. Ann Intern Med. 2007;146(3):157-166.

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