Effective July 1, 2008, the American Academy of Sleep Medicine (AASM) mandated the use of its new scoring manual1 by AASM-accredited sleep centers. The manual is largely consensus-based and does not meet scientific evidence levels of standard practice parameters. The task force members involved in the consensus did not have an opportunity to review the contents of the manual before its publication. The manual presents a number of technical and practical concerns that remain unresolved.2

The enforcement of the new manual coincides with changing policies regarding home sleep testing and, in some ways, facilitates its use. On the one hand, the manual calls for greater complexity in performing polysomnography, while on the other, it oversimplifies the scoring of respiratory events to such an extent that one might easily assume polysomnography is no longer required.

Shortly following the publication of the new manual, the AASM approved the use of limited-channel, unattended recording devices for diagnosing uncomplicated obstructive sleep apnea (OSA), stating that the new respiratory scoring rules should be used for scoring studies produced by these devices.3 However, to implement these rules, the event definitions must be further narrowed, because without recordings of the electroencephalogram (EEG), arousals can no longer be used as part of the scoring criteria.

SCORING OUT OF CONTEXT

The scoring of respiratory events in both children and adults, as presented by the new manual, focuses primarily on signals from respiratory transducers and oximetry, without taking into account normal variants of sleep/wake physiology. The only reference to neurophysiological data consists of a brief mention of arousal, as a possible criterion for the alternative hypopnea definition and as a criterion for the optional scoring of respiratory effort-related arousals (RERAs).

The manual also omits a discussion of artifacts, although these frequently confound the interpretation of respiratory events. The diagrams offered by the manual demonstrate only basic textbook-style events, without describing variants thereof, or relating them to other essential polysomnographic parameters. The scoring definitions are based on percentages of amplitude drops from baseline, although, in practice, such baselines do not really exist, since the signals are qualitative and continually distorted by arousal responses, body movements, postural changes, sensor shifts, mouth breathing, and other common phenomena seen in a typical sleep study.

The manual focuses, instead, on using specific technologies for specific types of events, implying that this improves the accuracy of data interpretation. The technologies described are not new—they have been available to the field for the past 25 years—and only the presentation has changed. In practice, all respiratory sensors have their drawbacks and limitations. The problem with the manual’s approach is the implication that if a particular sensor is used, all necessary information can be gleaned from it, without the need for a more global interpretation of the data. It has become common practice to scrutinize the size and shape of individual respiratory waveforms in an attempt to find abnormalities, while overlooking the bigger picture. This leads to an over-scoring of “imaginary events” that hold no clinical significance, while actual events may be overlooked or misinterpreted because they do not fit the models presented by the manual.

A GIANT STEP BACKWARD?

The basis for evaluating sleep disordered breathing was established nearly 40 years ago, when sleep researchers combined tracings from respiratory sensors with essential neurophysiological parameters, including the EEG, the recording of eye movements (EOG), and the recording of muscle activity (EMG). Although original definitions for apnea and hypopnea were similar to those described by the new manual, the scoring of these events has always been conducted within the framework of the EEG, EOG, and EMG.

In contrast, the new manual, and the new policies regarding home sleep testing, seem to deemphasize the physiology of sleep, promoting instead a purely rule-based, robotic approach to scoring respiratory events that can just as easily be replicated by a computer. In fact, most home sleep testing devices provide just that—an automated “analysis” of the data. Such a system may offer convenient diagnostic classification and rapid assignment to therapy, but will have clearly hazardous performance characteristics. And despite the AASM’s assertion regarding professional requirements for home testing, the primitive nature of these tests continues to hold the greatest appeal to those who are least qualified to perform them.

These combined developments represent a regression of the field that not only affects patient care, but also drives up treatment costs due to the high likelihood of over-scored, misinterpreted, false-positive studies. Thrown into the mix are the new bilevel positive airway pressure modalities, such as adaptive servo-ventilation (ASV), which are of great benefit when used appropriately, but are likely to be overused, based on the growing trend of oversimplified sleep evaluations, coupled with new industry-driven diagnostic labels, such as “complex sleep apnea.”

APPLYING THE NEW RULES

Regardless of one’s views on the subject, sleep practitioners seeking accreditation or board certification are required to follow the new “mandated recommendations.” Thus, the job of the clinician becomes twofold: do what is necessary to comply with the new requirements, yet do what is best for the patient. In other words, one can score according to the new manual, yet choose to describe and interpret the events based on a more comprehensive review of the data, combined with sound clinical judgment.

The visual rules for sleep stage scoring presented by the new manual are based on (and do not differ much from) the traditional Rechtschaffen and Kales (R&K) manual.4 A familiarity with R&K remains essential, because it forms a foundation for understanding the new manual. The descriptions of sleep stages presented by both manuals are based on normal subjects and do not address the many variants seen in routine clinical sleep studies, such as alpha-sleep, atypical EEG activations, medications effects, sleep fragmentation, recording artifacts, etc. This means that the scorer still has to use their judgment in applying the staging rules to abnormal recordings.

The optional bipolar EEG derivations (Fz/Cz and Fpz/Cz) described by the new manual are inappropriate because their use defeats the purpose of identifying waveforms relevant to sleep stage scoring (the waveforms are greatly attenuated by common mode rejection). Since publishing the manual, the AASM has acknowledged this error on its frequently asked questions (FAQ) Web site,5 although the proposed alternative Fpz/E1 derivation is equally incongruous.

As mentioned before, the new respiratory scoring rules do not differ much from definitions used in the past; therefore, as long as they are viewed and interpreted within the context of other essential PSG parameters, the results should not differ significantly from former PSG recordings. The main concern with following the respiratory rules to the letter is a tendency to over-score.

An important omission in the new manual is a lack of discussion regarding signal sensitivity settings and their relationship to the viewing size and aspect ratio of the data display. Historically, the sleep stage scoring display for adult patients has been based on a horizontal time scale of 10 mm per second and a vertical voltage scale of 5 µV per mm for the EEG, EOG, and EMG channels. Lower sensitivity settings, such as 7 µV/mm (or 10 µV/mm in children), have also been used, but signal detail and resolution may be compromised at these lower settings. This affects the accuracy of sleep stage scoring and arousal recognition, which in turn affects the interpretation of sleep-related events.

When PSG data are displayed on a computer screen, the actual size of the signals is further determined by the size of the screen, the size of the workspace within that screen, and, on some systems, the number of channels displayed on the screen. The default settings on some digital recording systems attenuate the signals to such an extent that accurate scoring becomes virtually impossible. This requires sleep technologists and physicians to make the necessary on-screen adjustments to achieve a more appropriate signal display.

The new scoring rules can serve as a foundation for comprehensive PSG evaluation, provided one understands their limitations and technical discrepancies, and provided one is able to see beyond basic definitions by exercising sound clinical judgment and common sense. Due to the relative lack of standardization and compatibility among recording systems, one also needs to understand how to fine-tune the data display on each system to achieve the best possible results (although in some instances, the ability to optimize the display may be limited by the system design).

WHAT ELSE CAN BE DONE?

It has become evident that, despite ongoing technological advancements, sleep recording and analysis methods have become compromised over the past few years. This could undermine the credibility of the field and potentially have a negative impact on patient care. By indiscriminately accepting mandates that are technically unsound and contradict basic scientific principles, we all contribute to a downward spiral that could eventually render the field less relevant.

On a positive note, a recent article published by the AASM regarding PAP titration presents a welcome contrast to the new scoring manual, whereby the authors clearly explain that their recommendations do not achieve evidence levels of practice parameters and should therefore be interpreted only as guidelines.6 The article further states that “these guidelines should not be followed in a ‘cookbook’ manner, but that sleep technologists and clinicians should combine their experience and judgment with the application of these recommendations to attain the best titration in any given patient.”

These statements give the articles far more credibility than if they were forced as a mandate, and they convey the message that optimal results cannot be achieved based solely on a set of narrow rules. It is hoped that future developments in the AASM will reflect this approach, so that good science, common sense, and sound clinical judgment can prevail.

The responsibility for promoting positive change involves everyone, including clinicians, technologists, and educators. We all need to do our part by not oversimplifying the work we do, by not blindly relying on technology, by not being naïve about the influence of industry upon the field, and by not passively accepting mandates that do not make sense.

In recent years, awareness of sleep disordered breathing has reached huge proportions, and everyone wants to become involved. Individuals with little or no experience in sleep are seeking to perform diagnoses, to administer treatment, and to give advice to those less discerning. Those of us who care about this field need to be careful not to compromise quality for the sake of profit or convenience. Instead, we can strive to revitalize the field by practicing good medicine; by educating ourselves, our patients, our referring physicians, and our communities; and by supporting and encouraging our leaders to do the same.


Nic Butkov, RPSGT, is education coordinator at the Rogue Valley Sleep Center, CEO of Synapse Media Inc, and director of the School of Clinical Polysomnography in Medford, Ore. He can be reached at sleepreviewmag@allied360.com.

References

  1. Iber C. Ancoli-Israel S, Chesson A, Quan SF; American Academy of Sleep Medicine. The AASM Manual for the Scoring of Sleep and Associated Events: Rules, Terminology and Technical Specifications. Westchester, Ill: American Academy of Sleep Medicine; 2007.
  2. Butkov N. Coming to consensus. Sleep Review. 2008;9(1):38-42.
  3. 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;3:737-747.
  4. Rechtschaffen A, Kales A. A Manual of Standardized Terminology, Techniques and Scoring Systems for Sleep Stages of Human Subjects. Los Angeles: UCLA Brain Information Services/Brain Research Institute; 1968.
  5. www.aasmnet.org/SMFAQs.aspx.
  6. Kushida CA, Chediac A, Berry RB, et al. Clinical guidelines for the manual titration of positive airway pressure in patients with obstructive sleep apnea. J Clin Sleep Med. 2008;4:157–171.