Grass Technologies is strong on endurance and a persistent leader in the development of high quality, reliable products for sleep and neurodiagnostic recording systems (www.grasstechnologies.com).

The Grass reputation of being the “gold standard” when it comes to reliability has followed the company since its inception in 1935.  The company’s long-standing history is a reflection of the faith that its customers have in its reputation of delivering quality products in a market where quality is often difficult to monitor.  Grass was there when sleep and EEG were in its infancy and played a vital role in the evolution of these fields.  Grass pioneered the design of the first EEG and sleep electroencephalographs and was a key player in the advancement of knowledge in these areas.  There are many things that set Grass Technologies apart from its competitors, but the most important fundamentals that customers count on again and again is the reliability of its exceptional products and the “Grass” commitment to customer service before, during and after the sale.

Reliable instrumentation builds customer confidence
Committed customers continue to purchase Grass products because the reliability factor has been maintained.   Although Grass was sold to Astro-Med, Inc in 1994, the Grass name and reputation have persisted.  Grass Technologies manufactures and develops numerous ancillary and support products and equipment that can be used in both sleep and other Neurodiagnostic applications.  The company offers the latest cutting-edge technology with high-end recording and analysis software set in uniquely dependable and sophisticated amplifiers. Reliable instrumentation for recording both ambulatory and laboratory-based sleep studies and EEG and long-term epilepsy monitoring are the backbone of its product line.  Grass offers a comprehensive line of clinical systems and is the only manufacturer that provides a lifetime warranty on all of its products, including amplifiers, head boxes, photic stimulators and other ancillary equipment.  Grass is able to offer this unique warranty because the company manufactures and develops all of its products in the United States in its Rhode Island headquarters and Massachusetts plant.  The company not only designs, manufactures and supports all of its products, but also sells them directly to its customers.  This allows Grass Technologies to make timely repairs and returns to its customers if a product malfunctions.

Customer support is an important part of the Grass tradition
With in-house engineers developing new hardware and software lines, Grass is able to offer a complete sophisticated group of instruments and accessories, including electrodes, sensors, amplifiers, stimulators, printers, video instrumentation and various sensors and transducers for monitoring EEG and sleep.  The team of dedicated designers and engineers ensure that the latest technology and instrumentation is delivered to its customers. Grass continues to thrive and grow in a tough economy due to consistent customer support and field sales coverage in the sleep and EEG markets.  The comprehensive development and product line of clinical systems offered by Grass Technologies is based on customer feedback.  The sales team stays in close touch with its customers through regular visits to determine how its products are being used, and to keep an ear on what the customers would like to see in their software package.  Customer support extends to “Grass College” which not only offers an opportunity for customers to receive advanced face-to-face training on the products purchased, but also a chance for new technologists to receive vital training.

Supporting sleep and neurodiagnostics is a part of the Grass tradition
Grass Technologies also has a reputation of contributing to and supporting education in both sleep and neurodiagnostics.  The company develops and provides educational products for the industry at no charge to its customers.  Customers using Grass Instrumentation currently employed in an EEG/PSG laboratory in the United States and Canada may request free Grass Educational Literature.  These products are incredibly useful for studying for exams and for training in schools and laboratories.

Grass continues to stand alone as a strong force in sleep and EEG diagnostics and manufacturing. The company is well financed, has no debt and is able to continue to offer the best products and support to its customers.  
Learn more about Grass Technologies at www.grasstechnologies.com

Marietta B. Bibbs is Manager of Sleep Disorders and Neurodiagnostics Departments at Morton Plant Mease Healthcare in Clearwater, FL and has worked in sleep medicine for the past 34 years. She is past President of the BRPT, has served on and chaired several BRPT committees and regularly participates in AAST programs as a speaker and lecturer.  Marietta is meeting coordinator for The Southern Sleep Society and is founder of the SE/SW Regional Association of Polysomnographic Technologists.

The Salter Labs® BiNAPS® and other select pressure transducers are utilized during sleep disorder studies to simultaneously measure respiratory airflow and snore pressure signals via a sleep diagnostic cannula.  When titration to CPAP is initiated it previously required switching to a snore microphone / sensor.  Now with the introduction of the new Salter Labs® SnoreTac™ Snore Sensing Adapter all that is required is for a sleep lab to utilize the SnoreTac™ Adapter with the existing sleep diagnostic cannula and place securely on the patient’s neck. The BiNAPS® will provide a clean snore signal with less signal artifact than traditional sensors. This eliminates the need for a snore microphone / sensor. This unique technology is disposable, single patient use and saves time and money, while eliminating the cleaning, damage and replacement issues associated with alternative snore sensors.

How was the SnoreTac™ developed and what is the science behind its operation?
The Salter Labs® SnoreTac™ was developed by engineers in the Salter Labs® R&D department in response to requests from sleep labs for a way to improve snore signals and utilize their existing BiNAPS® devices during CPAP titration to monitor snore.  The result is a small, light weight disposable adapter that attaches to the Salter Labs® sleep cannula and utilizes existing piezo sensor technology in the BiNAPS® to deliver a clean, accurate signal to the PSG equipment or other data acquisition system.

Who would benefit from using the Salter Labs® SnoreTac™?
The Salter Labs® SnoreTac™ will benefit all sleep labs using Salter Labs® BiNAPS® and other combination airflow pressure / snore devices, as well as, labs who are dissatisfied with their current snore microphone / sensors.

How will the Salter Labs® SnoreTac™ improve patient care?
The SnoreTac™ allows for improved detection of snore events with less  artifact, while providing a low cost disposable adapter that can be disposed of after each use

For more information, visit Salter Labs

Jeffory Wyscarver, marketing manager at CareFusion in Yorba Linda, Calif, believes the NOX-T3 portable sleep monitor could add fuel to a promising new year.

After spinning off from Cardinal Health’s clinical and medical products business in late 2009, San Diego-based CareFusion Corporation continues to build momentum. Thanks to a strategic partnership with Icelandic company NOX Medical, company officials say the mission to diagnose the legions of undiscovered sleep apnea patients is now within their grasp.

Wyscarver has made it one of CareFusion’s missions to diagnose patients who suffer the effects of obstructive sleep apnea, (OSA). The challenge now, he says, is attracting the reluctant (and less obvious) patients who want little or no part of in-lab, overnight studies. Wyscarver and others believe home sleep testing can fill those gaps without threatening the financial livelihood of sleep laboratories.

Growing a Sleep Lab’s Business

Can home testing actually grow the sleep lab business? For Wyscarver, the answer is an enthusiastic yes. The scenario might go something like this: a prospective patient calls a sleep doctor and relays a sleep complaint which coincides with a number of comorbidities such as congestive heart failure or morbid obesity. With these types of comorbidities, the physician will likely send the patient directly to a full sleep lab rather than have the test performed in the home. “Home testing, which is what the sleep labs are most afraid of, is something that is going to benefit them,” says Wyscarver. “When the message gets out that the sleep test can be done in the home, a lot more people who suffer from mild and medium sleep disorders are going to pick up the phone. We are convinced that home sleep testing will grow the in-lab hospital market.”

Opening the Bottleneck

When he joined CareFusion, Wyscarver worked hard to get NOX under the company’s umbrella. Now, CareFusion has an exclusive worldwide distribution agreement with NOX for all the products that they may develop related to sleep. The first major product under the agreement is the NOX-T3 portable sleep monitor, and both sides are happy with the relationship.

“Our hope was that we would be able to take sleep diagnostics and break open the bottleneck,” says Wyscarver. “The bottleneck is that if you have a sleep disorder and, you go to or call a sleep lab, they will often say come back in 6 weeks for your sleep test. Imagine if you showed up to a hospital or clinic with a broken arm, and they said come back in 6 weeks.

“Most would be horrified at the prospect of dealing with a broken arm for 6 weeks. Such is the case with most sleep labs,” continues Wyscarver. “And yet with apnea, a severe medical condition, it is acceptable to tell someone who can’t stay awake—and falls asleep while driving—that he should come back in 6 weeks. It is completely unacceptable.”

Transcending the Feature War

Under the body area network (BAN) monitoring approach, the NOX-T3 features an array of wireless sensors, including a Bluetooth® receiver. The Bluetooth is similar to a USB, with one port that can accommodate multiple items. “We are going to be pairing with up to 7 wireless devices,” says Wyscarver. “So at the moment we are pairing with a Bluetooth oximeter and a CO2 monitor. In mid-year 2010, we’ll pair with an auto titrating CPAP unit. When you couple the advanced technology with the ease of use, you can break open the diagnostic bandwidth and catch up with these apnea sufferers.”

Seeking to avoid mere variations on the same theme, Wyscarver hopes to transcend what he calls the ongoing feature war that has been raging for the last decade. “The challenge with wireless is to avoid the trap of getting enamored with the technology without thinking about the clinical benefits,” enthuses Wyscarver. “It may be trendy to say that it is wireless, but what is the clinical yield? What is the cost benefit? You must have good answers to those questions before implementing wireless technology.”

One of the problems with home testing is having the patient run the oximeter wire up the arm and down the chest, as this is fairly difficult for the average patient. For the patient, it is one of the vulnerable spots during recording. The additional task of unplugging an analog output cable from a CO2 monitor is also something that patients should not be asked to do. Both these tasks are made considerably easier with NOXT3′ s wireless technology.

NOX-T3

Ultimately, it boils down to an expansion of use for the product. “The NOX-T3 is for the sleep diagnostic market, but we are planning on going into the recovery room environment,” reports Wyscarver. “Also transitioning from invasive to noninvasive ventilation—and there are some channels there that pulmonologists want to monitor over time. The NOX-T3 platform can move to those environments with relative ease.

Wyscarver candidly observes that the NOX-T3 has thus far garnered a tepid response from sleep labs. Just one in nine of all NOX-T3s sold go to sleep labs, but CareFusion does sell an AASM-compliant full sleep lab system. “It is my opinion that the sleep community—established, accredited labs in hospitals— have taken a pass on home sleep testing,” says Wyscarver. “They feel the clinical outcome is not good enough and think if you don’t attend, and don’t have an EEG, it can’t be a sleep study. They don’t see the validity.”

“They also feel threatened financially in that if they start doing home testing, their revenue will be reduced, because if you do a study at home you are taking a person out of the in-lab scenario,” continues Wyscarver. “If you look at who is buying the NOX-T3, it is a clinician with an overweight patient, and the patient has no comorbidities. Why can’t a physician with a NOX-T3 recorder diagnose that patient with the assistance of the accredited sleep lab and board certified physician? Our biggest customers are working with board certified sleep physicians, not sleep labs.”

While pulmonologists have rightly dominated the sleep market for a long time, CareFusion has sold about 800 NOXT3s to cardiologists, a crucial and growing market. These clinicians appreciate the ease of use and the cost, which is on the lower end of the price range. FDA-approved for patients as young as 2 years old, CareFusion officials hope the NOX-T3, and additional products from the engineering team at NOX Medical, will continue to make an impact.

As home sleep testing continues to evolve, evidence-based outcomes will become more important and more available. With that in mind, Wyscarver reports that the University of Alberta recently began an extensive longitudinal pediatric

study to evaluate the impact of sleep disorders on overall pediatric health. Researchers will attempt to associate sleep disorders with pediatric disorders. “It is the largest study of its kind,” he says, “and they are going to use the NOX-T3 for their principle data collection system.”

NOX-T3 Portable Sleep Monitor at a Glance

• Wireless Bluetooth® Oximeter.
• Miniaturized technology: 88gram/79×63×21mm (with battery).
• Thorax & Abdomen RIP Effort + RIP Flow – RIP phase for paradoxical breathing.
• Integrated snore microphone with true audio signal.
• Gold Standard PSG Signals.
• Check waveforms real time.
• No accessible connectors/child safety battery door.
• Full featured type 3 device/Type 4 size and complexity.
• Flow signal through RIP Effort and/or nasal cannula.
• Wireless signals: SpO2, Pulse, Snore, Body Position.
• Off-the-shelf disposable or rechargeable batteries (AA).
• Inclusive analysis and reporting software.
• Extended applicability: pediatric, dental and ENT patients.
• Extensive review possibilities.
• Configurable data management.
• Multi-night recordings.

For more information about the NOX-T3, visit www.carefusion.com.

Review by Michael Clark
Director of Sales, Braebon, Ogdensburg, NY

MEDIBYTE – A NEW GENERATION PSG SCREENING DEVICE

We took a close look at all the available diagnostic screening units on the market and quickly realized there were deficiencies. This included product size, ease of use, reliability, performance and pricing. Also missing were any single enclosure screening devices that were directly  addressing the needs of the emerging dental and cardiology sleep medicine markets. Some companies were attempting to adapt their existing products to meet these new demands but no one was doing it well. So after consulting with numerous potential end users and sleep specialists we put together the development roadmap for a new generation PSG screening device. The end result was the new Medibyte diagnostic screener using patent-pending technology that is unique in the field of sleep medicine

MEDIBYTE’S UNIQUE FEATURES

First on the list is the performance per size ratio. The Medibyte has 10 channels packed into a single enclosure less than 3 square inches and weighing less than 3 ounces including the power source. Next, we focused on reducing power consumption allowing up to 24 hours of recording time using a single battery. The unit can also be programmed to go dormant for up to 30 days and then come alive and record back to back night studies. Included in the channel selection is a high sample rate auxiliary (AUX) port that can be programmed by the user to record a number of different signals including snoring sounds, EKG, EMG and EEG. Additional channels monitor dual effort, pressure, oximetry, pulse rate, body position and event markers. Finally, we made sure the enclosure was drop proof durable with extra strength LEMO connectors to increase reliability.

MEDIBYTE ACCOMMODATES DIVERSE AUDIENCES

All these features allow the Medibyte to be used in a number of different recording applications. For example, its small size makes it ideal for both adult and pediatric studies. Cardiologists entering into sleep medicine can program the unit for 24 holter recording while simultaneously measuring a number of sleep-breathing disorder parameters. Dental sleep professionals can now measure the true quantitative snoring sounds and db level with a microphone sensor sampled at 2000 Hz thereby allowing them to monitor the effectiveness of an oral device. General sleep testing facilities can use the unit to more accurately screen suspected sleep apnea patients since it provides much more information than just airflow and oximetry parameters.

MEDIBYTE IS EASY TO USE

The Medibyte is supplied with software that allows the user to program a number of preset configurations depending upon the application. We put considerable effort into making this an easy process that takes less than a minute to complete. Our goal was to make this procedure easy enough for a nine year to complete with little training and that was what we achieved. All the signals are downloaded from internal memory via USB for complete computer assisted analysis and full disclose review. A number of single page report templates are provided that detail snoring, sound level, respiratory, desaturation, leg movement and cardiac events related to body position. The user can accept the results from the computer analysis or edit any portion of the recording before printing a report.

MEDIBYTE BRINGS VALUE TO THE MARKET

The Medibyte was primarily developed to more accurately screen suspected SDB patients so they then can be quickly referred for a full PSG diagnostic study. As an example a busy cardiology practice could use a number of these units to screen their suspected patient group and monitor certain cardiac events at the same time. Since there is growing evidence suggesting a strong link between sleep disorders and cardiovascular consequences we believe this product will be incorporated into a number screening programs within cardiology driven sleep labs. Other areas of interest mentioned earlier that include pediatric and dental sleep will use this screener because it is so small and easy to use. It was never designed to replace the “gold standard” PSG study but only to assist and accelerate the diagnostic process of detecting many types of sleep disorders.

Review by Anna Rodriguez, RPSGT
Clinical Coordinator
Sleep Disorders Center of Virginia
Richmond, VA

SLEEPMATE SENSORS VALUED FEATURES

We do not use a lot of the movement sensors, however we do use an enormous amount of their snore sensors and effort belts. The snore sensors and effort belts are self-explanatory to use and understand their purpose. We use a lot of their pulse oximeters and cost-effective sense aid sensors that provide us with very clear signals. In summary, the valued features in this product that are extremely important to us, are its signal quality, sensor durability, costs efficiency, and ease of use. It was not necessary to train in using their products.

AFTER-SALES SUPPORT AND COMPATIBILITY ISSUES

SleepMate’s after-sales support is excellent. If I needed to order a product, I would have the utmost confidence that it would be here the very next day. Their customer service follows up routinely to make certain that we received everything we needed. There really is not much improvement that needs to be implemented there. However, some of the new sleep software systems are not compatible with the sense aid sensors that we are currently using. We recently upgraded two of our labs and unfortunately we were unable to use some sensors in those two labs because the new systems were not compatible with the sense aids

TIME-SAVING TRAINING PROGRAMS

We are in the process of hiring close to a dozen technicians and need training for them. It is going to be next to impossible to do the training in-house because there are so many trainees. Some of the trainees are people with little sleep experience. Therefore instead of doing our training in-house, we send the trainees to new education institutions that teach them the fundamentals of polysomnography. Normally students would be required to invest 80 hours in training, while SleepMate’s classes on the fundamentals of polysomnography can be completed within 40 hours. We are also able to use their educational CD’s in our training program because it covers everything from scoring to CPAP titrations to the fundamentals of sleep.

EDUCATIONAL COURSES

I have personally attended their classes and the degree of their education courses was top-notch. In my opinion, they are difficult to beat! I enrolled in the registry review class and everything was excellent in regards to the facility, the outline of the course and the depth of material covered. I recommend SleepMate educational courses to everyone who have little sleep background because the courses are designed to “break in” students with no prior sleep experience by adopting the go-easy-on-heavy-material approach. The end results prove to be extremely beneficial and such impressive educational courses have been needed for a long time.

David Barone

Obstructive Sleep Apnea

Obstructive sleep apnea (OSA) is defined as the cessation of airflow despite continuously respiratory effort. It occurs when the tongue and soft palate collapse onto the back of the throat, blocking the upper airway and causing air flow into the lungs to be interrupted. The temporary stoppage of air flow leads to gradual reduction in oxygen level and subsequent arousals. When in the partially awakening state, the airway contracts and opens, causing the obstruction in the airway to clear and for airflow to start again, resulting in a resumption of sleep. The severity of sleep apnea is defined by the frequency of interrupted airflow events during the night, the reduction in oxygen levels and the degree of sleep fragmentation caused those events.

Sleep apnea is associated with considerable effects on quality of life and patients’ general health. In addition to excessive daytime sleepiness, studies show that sleep apnea patients are much more likely to suffer from heart attack, congestive heart failure, hypertension, strokes, as well as having a higher incidence of work and driving related accidents.

Treatment Options

In addition to lifestyle changes, including good sleep hygiene, exercise and weight loss, there are three primary ways to treat sleep apnea. The most common method is nocturnal continuous positive airway pressure (CPAP) therapy. CPAP is applied through a tube which connects a bed-side device to a mask that covers the patient’s nose. The air pressure that is generated by the CPAP device splints the back of the throat and holds the airway open during sleep.

Other treatment modalities include the use of an oral appliance, a non-invasive therapy, which provides similar benefits to those available through CPAP, or, one of a number of surgeries to the soft palate, uvula and tongue to eliminate the excess tissue that collapses during sleep. Some patients may require more complex surgeries to reposition the anatomic structure of the mouth and facial bones in a manner that enlarges the airways.

Oral Appliance Therapy

Oral appliance therapy involves the fitting and use of a specially designed and custom fitted intra-oral device worn during sleep. Oral appliances are designed to enlarge the pharyngeal airway during sleep by repositioning and stabilizing the lower jaw and/or the tongue and by increasing the muscle tone of the tongue. The many FDA-approved oral appliances to choose from can generally be classified into one of the following categories:

• Tongue retaining appliances.
• Mandibular repositioning appliances.

Oral appliances are fitted and supported by dentists trained in this mode of therapy. The Academy of Dental Sleep Medicine has suggested the following criteria for use of oral appliance in the management of obstructive sleep apnea:¹

• Patients with primary snoring or mild OSA who do not respond to, or are not appropriate candidates for treatment with behavioral measures such as weight loss or sleep-position change;
• Patients with moderate to severe OSA who are intolerant of or refuse treatment with nasal CPAP;
• Patients who refuse treatment, or are not candidates for tonsillectomy and adenoidectomy, cranofacial operations or tracheostomy.

Advantages of Oral Appliance Therapy

Oral appliance therapy has several advantages:

• Treatment with oral appliances is non-invasive, adjustable and reversible;
• Many patients failing or refusing CPAP therapy find oral appliances to be comfortable and easy to wear after a couple of weeks of acclimation to wearing the appliance;
• Oral appliances can be easily carried when traveling, allowing uninterrupted therapy.

On-going Care

Once a patient diagnosed with OSA is fitted with an oral appliance, on-going care, including short and long-term follow-up, is an essential element in the continuing management of the patient. Follow-up office visits with the dental specialist who initiated the therapy should be scheduled at least every six months during the first year, and at least annually thereafter, in order to monitor patient adherence, evaluate device deterioration or maladjustment, evaluate the health of the oral structures and integrity of occlusion, and assess the patient for signs and symptoms of worsening OSA. The American Academy of Sleep Medicine, in its recently updated Practice Parameters for the Treatment of Snoring and OSA with Oral Appliances,² has recommended that an objective sleep study should be conducted for patients receiving an oral appliance after final adjustments of fit have been performed in order to assess the efficacy of the treatment.

Use of Portable Systems to Manage OSA

The primary means of confirming sleep apnea, following a review of medical history, symptoms and a physical exam, is to conduct a sleep study. Polysomnography (PSG), generally conducted in a hospital or in a standalone sleep laboratory facility, is considered as the most comprehensive sleep study, indicated for the diagnosis of nocturnal breathing disorders, neurological disorders such as narcolepsy and restless leg syndrome and parasomnia. In recent years, a large number of published reports have corroborated the use of new devices in providing an accurate and clinically effective diagnosis of OSA, as an alternative to PSG for many of the suspected patients.^3,4,5 Most such devices record a fewer number of physiological parameters compared to PSG, as they focus mostly on diagnosing nocturnal breathing disorders rather than neurological disorders. The reduced number of monitored channels and the corresponding simpler patient interface enable such devices to be used at patients’ homes, a venue offering not only greater convenience, but in many instances, an evaluation of the patient’s natural sleep patterns in a setting devoid of artifacts caused by the foreign environment in which PSG is conducted.

As the number of patients presented with symptoms of sleep apnea continues to increase, a growing number of healthcare providers have incorporated portable systems as an optional alternative to PSG studies. An appropriate application of portable devices by qualified clinicians may often result in an enhanced level of service and reduced cost for patients and payers. The use of portable devices may shorten the time from it takes to initiate treatments to at-risk patients and address special patients’ needs. Portable devices can also play a unique role during the continuing care and follow-up phase of patients with sleep apnea, since at-home studies may offer faster and more representative information, in comparison to in-hospital PSG, when assessing the efficacy of a new therapy, or after making changes in ongoing treatment parameters.

The role of portable devices (also referred to as ‘ambulatory’ or ‘Level 3´) in ruling-out or confirming sleep apnea, or in the continuing management of the disease, is being continuously evaluated by professional societies, health plans and other healthcare policy groups, such as Minneapolis-based Institute for Clinical Systems Improvement (ICSI), which has recently suggested the following guidelines:⁶

“In patients with a high pretest probability of OSA, unattended portable recording for the assessment of obstructive sleep apnea is an acceptable alternative to standard polysomnogram in the following situations

1. Patients with severe clinical symptoms that are indicative of a diagnosis of obstructive sleep apnea and when limitation of treatment is urgent and standard polysomnography is not readily available;

2. For patients unable to be studied in the sleep laboratory, and

3. For follow-up studies when diagnosis has been established by standard polysomnography and therapy has been initiated.”

“Employment of portable monitoring as a second-best option is not likely to result in harm to patients with a high pretest probability of OSA, and may result in less risk than leaving the condition undiagnosed.”

The Watch-PAT

The Watch-PAT (manufactured by Itamar Medical Ltd.) is an advanced diagnostic system for OSA. Initially approved by the FDA in 2001 as a portable system intended for the diagnosis and assessment of OSA, the Watch-PAT is one of the most user-friendly systems currently available, extracting the physiological information required to determine the presence and severity of OSA using a small wrist-mounted device connected to two sensors attached to the patient’s fingers. The Watch-PAT minimal and highly compact patient-device interface is dramatically contrasted with other portable systems which collect data during the night through a larger number of sensors, including some attached to the patient’s face and chest and connected by long wires to the device itself. Such sensors, in addition to contributing to patient anxiety and discomfort during sleep, are also at a higher risk of falling off during the night, compromising the quality of the data.

The Watch-PAT unique patient’s interface enables the reliable use of the system in patients’ homes, eliminating many of the variables and inaccuracies presented in studies conducted outside the natural and regular sleeping environment. Instructing the patient on operating the single-button Watch-PAT and mounting the two external sensors is generally accomplished in less than ten minutes. Once the study is completed, the information collected during the night is downloaded automatically into a standard office PC (pre-loaded with the data analysis software). This data is than analyzed (‘scored’) and within a few minutes a report is generated on the screen and a hard copy is printed. The automatic data analysis offers consistency, repeatability and accuracy unmatched by the variability of manual scoring. While in most instances only the final report is required to assess severity of sleep apnea or to evaluate the efficacy of a therapy, the entire raw data collected during the study is still available for review, further analysis or documentation.

Although the raw data is acquired from a small number of sensors embedded or attached to the Watch-PAT, the amount of clinical information provided at the completion of the study is significant. The Watch-PAT reports include all information required to accurately assess and quantify the severity of the sleep apnea, including values of all common indices, such as AHI, RDI, ODI and heart rate. In addition, the Watch-PAT also identifies and records sleep, wake and REM states, providing measures of respiratory and apnea indices based on actual sleep time, rather than ‘bed time’. The Watch-PAT is actually the only system that provides this important information without attaching EEG sensors to the patient’s skull. This sleep data enables a clinician managing any of the optional therapies to evaluate the quality of sleep pre and post intervention, and make necessary adjustments, when necessary. Sleep architecture and fragmentation can be assessed and quantified, including confirmation that the patient has entered and received sufficient amount of REM sleep.

The Watch-PAT is being used on a regular basis in a diverse range of medical establishments, including academic and community hospitals, stand-alone sleep labs, physician offices, as well as dentists specializing in oral appliance therapy. The large body of clinical experience accumulated in recent years is reflected in the extensive list of publications, reporting on multiple validation and outcome studies.7

sleep apnea have incorporated the Watch-PAT into their respective protocols, taking advantage of its versatility, accuracy and simple patient’s interface. Following recommended practice guidelines, such specialists use the Watch-PAT to identify optimal settings of the device, demonstrate and document treatment efficacy, or rule-out sleep apnea before fitting an appliance to patients seeking relief for primary snoring.

The primary goals of oral appliance therapies include lowered AHI, reduced daytime fatigue and significantly attenuated snoring. Once an appliance is fitted, it is recommended that an assessment is made to demonstrate and document treatment efficacy. In practices using the Watch-PAT, patients can now be evaluated objectively, measuring their breathing disturbances and sleep quality with and without the appliance in place. Until incorporating the Watch-PAT, dentists fitting oral appliances had to rely on patients’ own reports on how well the treatment works, or send patients for a PSG study in one of the local sleep labs to objectively evaluate treatment efficacy. In some situations, patients were equipped with pulse oximetry for an in-home recording. While PSG provided the required information, it was in most instances associated with significant time delays, inconveniency to the patients and an additional significant cost outlays to patients or their health plans. Oximetry studies, while conducted at the privacy and convenience of patients’ homes, simply do not provide sufficient clinical information to appropriately determine treatment efficacy. Most other portable devices used by dentists for this purpose lack data on actual sleep patterns and quite often, are too cumbersome for most patients to handle independently.

Some practices use the Watch-PAT to only evaluate the actual and absolute level of apneas once the appliance has been properly titrated, as determined by patient’s own report on improvement in his or her sleep and daytime fatigue. Other practices record data using the Watch-PAT, first without the appliance and than again, with the oral appliance in place. Having two Watch-PAT studies, one serving as the base line and the other as a post-intervention record, each with numerical and graphical summaries of breathing patterns, apnea indices, oxygen desaturation levels, sleep time and amount of REM sleep, allow for an easy, simple and accurate assessment of the effectiveness of the treatment. Most dentists review the reports with their patients, and when requested, provide copies to their primary care physician and/or the diagnosing sleep lab to assist in additional follow-up, as needed.

Typically, the studies with the Watch-PAT are conducted a number of weeks after initiation of therapy in order to assess the ‘steady state’ performance. In certain cases, especially those associated with patients presented with extremely high AHI, if studies point to insufficient therapeutic results in spite of an elaborate and methodical titration process, such patients are referred back to the sleep lab for a retry of CPAP therapy, potentially in conjunction with an oral appliance. In certain situations patients may also be advised to seek an opinion about one of the surgical options.

A number of specialists have modified their protocol to better accommodate local practices or to better integrate their efforts with the local sleep labs. In one of the active practices contacted for this report, patients are instructed to adjust their device until they realize significant reduction in their pre-treatment symptoms, including less daytime fatigue, improved alertness and reduced snoring. A sleep study using the Watch-PAT is than being conducted to confirm low AHI, acceptable sleep architecture and sufficient REM. Once this is done, patients are referred back to the sleep lab that has performed the original diagnosis, where they undergo a full-night PSG coupled with an in-lab oral appliance titration. Recent analysis conducted by the practice confirmed that the current protocol does achieve the optimal setting for most patients, although in certain cases, the final PSG/titration study suggests further adjustment of the appliance.

Most patients seen today by oral appliance specialists have already been diagnosed in a sleep lab and in most instances have tried and failed, or simply refused, CPAP treatment. Yet, some patients are self-referred, typically with complaints of heavy snoring. While some dentists send all such patients for a PSG in one of the local sleep labs, some will conduct a series of evaluations, including an assessment of daytime sleepiness, physical evaluation and medical history, and, if as a result of such evaluations determine that a given patient is unlikely to have sleep apnea, will order a study with the Watch-PAT to obtain a final and conclusive confirmation of primary snoring with no sleep apnea. Some of these self-presenting patients may have had a sleep study years ago, and after failing CPAP have remained untreated for long time and are now considering resumption of therapy with an oral appliance. Such patients are generally encouraged to undergo a new PSG study to evaluate their current sleep apnea. Some practices, when encountering patients that simply refuse or are otherwise unable to undergo an in-lab PSG, will conduct a home study as an alternative, as suggested by the respective guidelines. Some dentists have been trained in the diagnosis of sleep apnea and thus, review the study results themselves in order to determine suitability for treatment, while other dentists rely on a review of the data by a sleep specialist to advise them before proceeding with therapy.

In addition to offering a methodical clinical pathway and verification of treatment efficacy, the Watch-PAT contributes also to overall patients’ satisfaction. As most patients are already experienced with an in-lab PSG study performed for their primary diagnosis, they recognize the pros and cons of the Watch-PAT study. Indeed, dentists offering their patients the Watch-Pat as an alternative to an additional PSG point to a high degree of satisfaction from these patients who appreciate the convenience and privacy of the at-home study, and at times, its lower cost, especially when they are responsible for a considerable portion of the charges of the test as a result of deductibles or a significant co-pay.

Summary

The number of patients seeking treatment for sleep apnea is increasing rapidly, in tandem with the growing understanding of the debilitating effects of the disease and its implications on quality of life and other serious morbidities. CPAP is considered the first and preferred mode of therapy for sleep apnea. However, in-spite of many improvements made in such devices, significant percentage of patients requiring therapy either resist the treatment or fail to comply with it over time. Other than changes in lifestyle and significant reduction in weight, the only other non-invasive option available for these patients is use of an oral appliance therapy. Once used mostly for primary snoring, such appliances are now recommended for patients with mild and moderate, and in certain instances, even severe sleep apnea. A growing number of dentists are now providing oral appliance therapy to larger numbers of patients referred to them by sleep specialists after these patients have failed CPAP therapy, or self-referred patients, especially those seeking relief from snoring. Guidelines published by the Academy of Dental Sleep Medicine emphasize the importance of conducting follow-up studies for such patients. The Watch-PAT system provides friendly patient’s interface and ability to measure breathing parameters and oxygen desaturation levels, as well as sleep time and quality. The Watch-PAT is quickly becoming the system of choice for dentists involved in the delivery of oral appliance therapy, replacing older, less sophisticated and more cumbersome systems, or providing an alternative to repeat PSG studies on one hand, or reliance on clinically-limited measures such as pulse oximetry, on the other hand. Primary application of the Watch-PAT within an oral appliance practice is during the assessment of optimal titration of the appliance and in generating treatment efficacy records. Other applications of the Watch-PAT include identifications of failed oral appliance therapy, or using it to rule-out sleep apnea in patients complaining about snoring. Patients’ response to the Watch-PAT studies is highly favorable, and all clinicians contributing to this report have expressed high degree of satisfaction with the system.

References

1. http://www.dentalsleepmed.org/OralApp.aspx
2. “Practice Parameters for the Treatment of Snoring and OSA with Oral Appliances: An Update for 2005” American Academy of Sleep Medicine Report, 2005, Sleep, Vol. 29(2), 240–243.
3. Bar A, Pillar G, Dvir I, Sheffy J, Schnall RP, Lavie P. Evaluation of a portable device based on arterial peripheral tonometry (PAT) for unattended home sleep studies. Chest, March 2003, 123(3):695–703.
4. Pittman DS, Ayas NT, MacDonald MM, Malhotra A, Fogel RB, White D. Using a Wrist-Worm Device Based on Peripheral Arterial Tonometry to Diagnose Obstructive Sleep Apnea: In-Laboratory and Ambulatory Validation. Sleep 2004, Vol.27 (5), 923–933.
5. Penzel T, Kesper K, Pinnow I, Becker FH, Vogelmeier C. Peripheral arterial tonometry, oximetry and actigraphy for ambulatory recording of sleep apnea. Physiol. Meas. 25 (2004) 1–12.
6. ICSI, Diagnosis and Treatment of Obstructive Sleep Apnea, Third Edition, March 2005.

Philip R. Westbrook, MD, Michael J. Dickel, PhD, Dennis Nicholson, MD, Daniel J. Levendowski, MBA, Timothy Zavora, BS, Vladimir Simeunovic, BS and Roy Dalati, BS

Abstract

Objective: To compare two commercially available limited channel systems utilizing in-home self-applied recorders to each other and to standard in-laboratory attended nocturnal polysomnography (PSG) for the diagnosis of obstructive sleep apnea.

Study Design: A sequential trial with blinded comparison.

Methods:Each of 24 male patients suspected to have obstructive sleep apnea had three diagnostic studies performed. The participants first completed a self-administered NovaSom™ QSG™ (NovaSom), followed by a standard full-PSG, and then a self-administered Apnea Risk Evaluation System (ARES™) study. Both portable Level III systems were compared to PSG as the benchmark, using PSG AHI of 15 as the diagnostic cutoff.

Results: Twenty of 24 patients successfully completed the study. No failure of the in-home systems occurred. Both systems compared favorably in diagnostic accuracy to the PSG. The sensitivity, specificity, positive predictive value, and negative predictive value for the ARES were 100.0, 83.3, 93.3, 100.0; for the NovaSom–4% desaturation criteria were 78.6, 100.0, 100.0, and 66.7; and for the NovaSom–2% desaturation criteria were 85.7, 83.3, 92.3, and 71.4 respectively.

Conclusions:Both limited channel systems worked reliably when self-applied in the home and demonstrated acceptable accuracy when compared to polysomnography for diagnosing obstructive sleep apnea in this selected population.

Introduction

Obstructive sleep apnea (OSA) is a disorder characterized by frequent episodes of sleep induced obstructed breathing accompanied by hypoxemia and terminated with brief unremembered arousals. It has been documented as a prevalent chronic affliction of persons living in industrialized countries, causing disabling symptoms and potentially doubling healthcare utilization and cost^1–6. The disorder has also been identified as a significant risk factor for accidents, cardiovascular disease and diabetes. In spite of the fact that effective treatment exists, in the United States it is estimated that only a small fraction of the 20 million^{7, 8} individuals estimated to suffer with OSA have been diagnosed. In part this may reflect ignorance about the disease on the part of health care providers. However, it has also been opined that the usual diagnostic evaluation is limited by cost and, in some cases, availability.⁹ The “gold standard” test, in-laboratory attended polysomnography (PSG), while expensive, is supported by current reimbursement policies.

In 2003, a joint task force of the American Thoracic Society the American Academy of Sleep Medicine, and the American Academy of Chest Physicians found insufficient medical evidence to support the efficacious use of portable monitoring.^10–12 Medicare followed with a decision which disallowed reimbursement for continuous positive airway pressure (CPAP) if portable monitoring was used for the diagnosis of OSA. Following Medicare’s policy change, many managed care groups and insurers chose not to reimburse for an in-home unattended study. The only positive outcomes of the task force findings, with respect to portable monitoring, were recommended study design guidelines for assessing the efficacy of limited channel, unattended systems intended for the diagnosis of OSA in the home. These guidelines provide a blueprint for assessment of in-home OSA testing using an evidence-based approach.

During recruitment of patients for an ongoing study, an opportunity was provided to compare the diagnostic capabilities of two of the systems that meet the requirements for a Type 3 Device (Modified Portable Sleep Apnea Testing) when used unattended in-home. At that time, the VA Long Beach Healthcare System had just begun referring patients for NovaSom (NovaSom™ QSG™, Sleep Solutions, Pasadena, MD) in-home studies as a means to reduce its patient backlog. The VA Long Beach Healthcare System was a referral source of patients for the ARES™ (Apnea Risk Evaluation System, Advanced Brain Monitoring, Carlsbad, California) validation study. Subsequent to the acquisition of these data, both portable monitors were validated in the home13–15 in a combined total of 272 comparisons with PSG. This study provided an opportunity for an independent “real world” evaluation of how the NovaSom and the ARES compared to each other and how well they each compared to PSG.

Methods

Twenty-four consecutively recruited individuals scheduled for a NovaSom study by the Sleep Center at the Veteran’s Administration Long Beach Healthcare System participated in this study. All subjects completed the NovaSom in-home study first, followed by overnight PSG, and then the ARES Unicorder™ in-home study. Typically, a month lapsed before all three studies were completed. This study protocol was approved by the Institutional Review Boards of Advanced Brain Monitoring, with deferring approval by the Pomona Valley Hospital and the Veteran’s Administration Long Beach Healthcare System Institutional Review Boards. Informed consent was obtained from all subjects.

For the unattended NovaSom study, three nights of data were acquired in-home. The NovaSom acquires oxyhemoglobin saturation (SpO₂) and pulse rate using a transmittance finger probe, snoring sounds and airflow derived from snoring sounds using a microphone, and respiratory effort by means of a chest piezo belt. The NovaSom includes audio alerts to notify the user when transducers have become detached. The signals are processed in real time to detect abnormal breathing and summary data is saved to a bedside recorder. The NovaSom system did not monitor head or body position. Patients were mailed the device and self-applied it using written and video instructions. A photo of the NovaSom System is presented in Figure 1.

The PSGs were performed at a community hospital-based American Academy of Sleep Medicine accredited Sleep Disorders Center using Sandman Elite V6.2 hardware and software (Nellcor Puritan Bennett, Kanata, ON). Signals included: electroencephalogram (EEG) (C4-A1, C3-A2, O2-A1, O1-A2), electrooculogram (EOG), submental and bilateral tibial electromyogram (EMG), electrocardiogram (ECG), airflow (nasal thermistor and nasal pressure (PTAF2, Pro-Tech Services, Woodinville, WA)), chest and abdominal motion (piezo bands), SpO2, and snoring intensity. An ARES Unicorder was worn concurrently during the PSG to obtain head position data.

For the unattended ARES study, two nights of data were acquired in-home with the ARES Unicorder. The Unicorder is a single, forehead site device that records the optical signals used to derive SpO₂ and pulse rate, head movement and head position (accelerometers), and snoring sounds (microphone). (The model Unicorder used in this study did not include a measure of airflow). The Unicorder provides audio and visual alerts to notify the user when it is incorrectly affixed or when signal quality is poor. The full disclosure recording is downloaded and processed off-line to detect obstructive breathing during sleep. The Unicorder was mailed to the patient who self-applied it following written instructions. A photo of the Unicorder is presented in Figure 2.

Sleep Solutions and Advanced Brain Monitoring provided telephone technical support as necessary to patients using their respective devices. Of the twenty-four patients who were studied, the data from four subjects were unusable. Two cases were dropped because the patients were unable to sleep during their PSG (i.e., sleep time < 1.5 hours). One PSG record was unusable due to an incorrect setting of the averaging window of the pulse oximeter. The fourth patient was dropped from the study because of severe chronic obstructive pulmonary disease (COPD) which precluded him from being a candidate for unattended in-home OSA testing. No patients had to be dropped from the study because of failure of the in-home recording.

Apneas and hypopneas were visually scored in the PSG records by trained technologists and reviewed by a physician board-certified in sleep medicine. A desaturation threshold of 3% was required for all apnea and hypopneas used in the calculation of the apnea hypopnea index (PSG-AHI). The NovaSom data were analyzed using proprietary automated scoring algorithms. Because the NovaSom reports RDI based on a 2% and 4% desaturation level, both results were analyzed. The ARES-DI was computed using rules previously described13 relying primarily on the oximeter to determine abnormal breathing. A stepped approach that adapts based on the SpO2 level prior to the start of the desaturation was used to determine the necessary desaturation level (i.e., ranging from a desaturation plus resaturation of 2.2% and 2.2% when the start of the desaturation = 95% to 4.0% and 3.2% when the start of the desaturation was < 88%). Changes in heart rate and head movement indicative of arousals were used to confirm desaturations when the 2.2% threshold was applied. The definition for the PSG-AHI was the total number of abnormal breathing events divided by the hours of sleep, and the definition for the ARES-RDI and NovaSom-RDI was the total number of abnormal breathing events divided by the hours of recording time. The term RDI refers to the in-home studies and AHI refers to the PSG studies to distinguish between the use of total recording time and total sleep time. A clinical cut-off of 15 was used for the AHI/RDI. All parties involved in reviewing the data (PSG or in-home) were blinded to the results of the other systems. The average duration of the 20 completed PSG studies was 5.9 hours. The average valid recording time across both nights of the ARES studies was 11.4 hours. The average time-in-bed across the three nights of NovaSom studies was 18.1 hours.

The kappa coefficient was used to assess the beyond-chance agreement between the ARES-RDI, the NovaSom-RDI and PSG-AHI, without using the assumption that the PSG was the “gold-standard” comparison. Clinical cut offs of AHI = 10, 15, 20 and 30 were used to derive the Receiver Operator Characteristics of the two systems. Pearson correlations were used to compare the PSG-AHI vs. the ARES-RDI, NovaSom-2% RDI and Novasom-4% RDI.

Correlation analysis was also applied to the differences between the PSG-AHI and the ARES-RDI in all positions vs. only supine. It was also used to assess the relationship between the percentage of time supine during PSG compared to the percentage of time supine across both nights of ARES in-home recordings.

Results

Table 1 presents the cross tabulations of the ARES and NovaSom vs PSG comparisons used to compute the statistical results shown in Table 2. The kappa coefficients for the PSG vs. ARES (0.88), NovaSom-4% (0.69) and NovaSom-2% (0.66) indicate an excellent agreement beyond chance (Table 2). The ARES provided greater sensitivity than the NovaSom-4% or NovaSom-2% (100% vs. 78.6% and 85.7%, respectively). The NovaSom-4% provided better specificity than the ARES or NovaSom 2% (100% vs. 83.3% and 83.3% respectively). The NovaSom-4% provided a slightly better positive predictive value as compared to the ARES or NovaSom-2% (100% vs. 93.3 and 92.3, respectively). The ARES provided a substantial improvement in negative predictive value as compared to NovaSom-4% and NovaSom-2% thresholds (100% vs. 66.7% and 71.4%, respectively).

The Bland-Altman plots for the ARES-RDI, NovaSom-4% RDI and NovaSom-2% RDI vs. PSG-AHI are presented in Figures 3.a., 3.b., and 3.c., respectively. Novasom-4% exhibited the greatest bias (-5.6 events/hr) as compared to the ARES (-3.1 events/hr) and Novasom-2% (-2.8 events/hr). The ARES provided smaller standard deviations about the mean (6.3 events/hr) compared to NovaSom-4% (8.7 events/hr) and Novasom-2% (9.7 events/hr) (Figure 3). The correlation between the PSG-AHI and ARES-RDI was 0.93. The corresponding correlation for the NovaSom-4% RDI and NovaSom-2% RDI vs. PSG-AHI was 0.86 and 0.82, respectively.

A tabular presentation of the Receiver Operating Characteristics of the ARES and NovaSom vs. PSG is presented in Table 3 for clinical cut offs of AHI = 10, 15, 20, and 30. The NovaSom-2% provided perfect sensitivity and specificity with a clinical cut off of 10; the ARES provided a poorer specificity and the NovaSom-4% provided a poorer sensitivity. At all other clinical cut offs the ARES and NovaSom-2% and NovaSom-4% provided similar specificities while the ARES provided similar or better sensitivity.

To assess influence of position on the PSG-AHI and ARES-RDI, the differences between the ARES-RDI and PSG-AHI were computed across all positions and only in the supine position. The correlation between these two measures was 0.65. The correlation between the percentage of time supine during full-PSG (no split night studies) and across two nights of in-home recordings was 0.66.

Discussion

Recently a number of policy decisions have been published which, taken together, potentially impact the use of portable monitoring. First, the Institute of Medicine, in a published report, urged the evaluation and validation of existing diagnostic technologies to assist in the diagnosis of millions of undiagnosed individuals suffering from sleep disorders.¹⁶ Shortly thereafter, the American Academy of Sleep Medicine (AASM) issued practice parameters for Portable Monitoring in the Diagnosis of Obstructive Sleep Apnea.¹⁷ The AASM recommended that accredited sleep laboratories and board certified Sleep Specialists use portable monitoring when combined with a clinical assessment, and that the therapy decision be based on both the results of the study and knowledge of the individual patient’s symptoms. It appears that insurers are now following with modifications to their coverage position that includes the use of portable monitoring devices (level III) when PSG is not readily available, the patient is unable to be studied in the laboratory, or a home study is being used to evaluate the treatment rendered after the diagnosis of OSA has been established by a previous PSG or home sleep study.¹⁸

As recommended by the Institute of Medicine, both Type III devices used in this study were previously validated. The ARES was validated both concurrently with PSG 324 studies (261 patients and 63 presumably healthy controls) and in 227 unattended in-home study comparisons (172 patients and 55 controls).^13,14 The NovaSom was previously validated concurrently with PSG in 101 patients and in 45 unattended in-home comparisons.¹⁹ Each system has been compared to PSG using procedures that minimized bias. Studies have been performed in an unattended setting and failure rates/lost data of the system were reported.

In this comparison study, both the ARES and NovaSom provided an effective alternative to laboratory-based PSG in a population of Veteran’s Administration patients. Differences in the sensitivity and specificity of the NovaSom and ARES (Table 2) as compared to previous reports ^{13, 14, 19} may be attributed to the small sample size in this study (n = 20). The ARES and NovaSom bias toward under-reported severity in patients with PSG-AHI levels above 60 is most likely attributed to additional recording time. The sensitivity of the NovaSom-4% was clearly influenced by the 4% desaturation requirement, as compared to the ARES stepped approach and the NovaSom-2%, as a result of the 3% desaturation requirement used to compute the PSG-AHI. In a previous report, the majority of the differences between the PSG-AHI and ARES-RDI that resulted in misclassifications were attributed to the influence of head position.¹³ Head position again appeared to explain some portion of the differences between the PSG-AHI and ARES-RDI. Analysis of the influence of position (head or body) on the NovaSom results was not possible because this measurement is not obtained

The benefit of using multiple testing nights as a means to improve the diagnostic accuracy of OSA is beginning to emerge. Recent studies suggest that at least 10% of sleep-disordered breathing cases would be misclassified based on only one night of data.²⁰ Time-in-position was a primary source of misclassifications between in-home and PSG studies ¹³ and substantial night-to-night variability in head position during sleep was observed in that study. The use of automated scoring software reduces the labor required to hand-score multiple night of data, and eliminates inconsistencies introduced by human scoring. ^21–23 The analytical techniques used for the ARES auto-scoring have been fully described;¹³ the NovaSom methods have not been described. An advantage of the ARES over the NovaSom is that full-disclosure recordings are acquired that can be visually inspected and hand-scored if necessary to verify the automated scoring algorithms. This capability is useful in the diagnosis of difficult cases or when less than optimal signal quality is acquired. Both the ARES and NovaSom include on-line monitoring and user warning alarms to assist the patient and ensure that high quality recordings are acquired, a feature unique to these two systems.

The patient with COPD provided a case study example of someone with a severe breathing impairment who is not a candidate for an for in-home OSA testing. During the PSG study the patient’s desaturation levels were below 50%, resulting in the attending technician calling emergency personnel. Patients hard of hearing (i.e., unable to respond to the alerts), or who suffer from severe arthritis, dementia, have cardiac arrhythmia, congestive heart failure or are on supplemental oxygen use at night are also not considered appropriate for unattended OSA diagnostic testing. Limited channel systems such as the ARES and NovaSom cannot be used to diagnose narcolepsy or sleep-related movement disorders.

This study confirms that both systems provide acceptable diagnostic accuracy in an unattended setting compared to laboratory PSG in a sample of VA patients suspected of having OSA.

Acknowledgements

The authors wish to thank Michele Burnett and George Wirtes from Pomona Valley Hospital Sleep Disorders Center, and Nancy Daily of the VA Long Beach Healthcare System for their assistance in managing the clinical studies and preparing the data.

References

1. Smith R, Ronald J, Delaive K, Walld R, Manfreda J, Kryger MH. What are obstructive sleep apnea patients being treated for prior to this diagnosis? Chest. 2002;121(1):164–172.
2. Kryger MH, Roos L, Delaive K, Walld R, Horrocks J. Utilization of health care services in patients with severe obstructive sleep apnea. Sleep. 1996;19(9 Suppl):S111–S116.
3. Kapur VK, Redline S, Nieto FJ, Young TB, Newman AB, Henderson JA. The relationship between chronically disrupted sleep and healthcare use. Sleep. 2002;25(3):289–296.
4. Cooney RN, Haluck RS, Ku J, et al. Analysis of cost outliers after gastric bypass surgery: what can we learn? Obes Surg. 2003;13(1):29-36.
5. Ronald J, Delaive K, Roos L, Manfreda JH, Kryger MH. Obstructive sleep apnea patients use more health care resources ten years prior to diagnosis. Sleep Res Online. 1998;1(1):71–74.
6. Bahammam A, Delaive K, Ronald J, Manfreda J, Roos L, Kryger MH. Health care utilization in males with obstructive sleep apnea syndrome two years after diagnosis and treatment. Sleep. 1999;22(6):740–747.
7. National Sleep Foundation. Sleep Facts and Stats. http://www.sleepfoundation.org/NSAW/pk_sleepfacts.cfm.
8. Young T, Palta M, Dempsey JA, Skatrud J, Weber SM, Badr MS. The occurrence of sleep-disordered breathing among middle-aged adults. N Engl J Med. 1993;328:1230–1235.
9. Pack AI. Sleep-disordered breathing: access is the issue. Am J Respir Crit Care Med. 2004;169(6):666–667.
10. Executive summary on the systematic review and practice parameters for portable monitoring in the investigation of suspected sleep apnea in adults. Am J Respir Crit Care Med. May 15 2004;169(10):1160–1163.
11. Chesson AL, Jr., Berry RB, Pack A. Practice parameters for the use of portable monitoring devices in the investigation of suspected obstructive sleep apnea in adults. Sleep. Nov 1 2003;26(7):907–913.
12. Flemons WW, Littner MR, Rowley JA, et al. Home diagnosis of sleep apnea: a systematic review of the literature. An evidence review cosponsored by the American Academy of Sleep Medicine, the American College of Chest Physicians, and the American Thoracic Society. Chest. Oct 2003;124(4):1543–1579.
13. Westbrook P, Levendowski D, Cvetinovic M, et al. Description and validation of the apnea risk evaluation system: a novel method to diagnose sleep apnea-hypopnea in the home. Chest. Oct 2005;128(4):2166–2175.
14. Reichert JA, Bloch BA, Cundiff E, Votteri BA. Comparison of the NovaSom QSG, a new sleep apnea home-diagnostic system, and polysomnography. Sleep Medicine. 2003;4:213–218.
15. Ayappa I, Rapoport D, Westbrook P, Levendowski D, Zavora T, Norman R. Validation of a Self-Applied Unattended Monitor for Sleep Disordered Breathing (SDB). Sleep. 2006;29(Abstract Supplement 29):A343.
16. Committee on Sleep Medicine and Research. Ensuring Adequate Diagnosis and Treatment: Access, Capacity, and Technology Development. In: Colten HR, Altevogt BM, eds. Sleep Disorders and Sleep Deprivation: An Unmet Public Health Problem. Washington, D.C.: The National Acadamies Press; 2006.
17. American Academy of Sleep Medicine. Portable Monitoring in the Diagnosis of Obstructive Sleep Apnea. Journal of Clinical Sleep Medicine. 2006;2(3):333.
18. CIGNA HealthCare Coverage Position: Home Sleep Studies for Obstructive Sleep Apnea: CIGNA Health Corporation; 2006.
19. Claman D, Murr A, Trotter K. Clinical validation of the Bedbugg in detection of obstructive sleep apnea. Otolaryngol Head Neck Surg. 2001;125(5):227–230.
20. Stepnowsky CJ, Orr WC, Davidson TM. Nightly variability of sleep-disordered breathing measured over 3 nights. Otolaryngology. 2004;131(6):834–843.
21. Norman RG, Pal I, Stewart C, Walsleben J, Rapoport DM. Interobserver agreement among sleep scorers from different centers in a large dataset. Sleep. 2000;23(7):901–907.
22. Whitney CW, Gottlieb DJ, Redline S, et al. Reliability of scoring respiratory disturbance indices and sleep staging. Sleep. 1998;21(7):749–757.
23. Collop NA. Scoring variability between polysomnography technologists in different sleep laboratories. Sleep Medicine. 2002;3

Clifford A. Massie, PhD and Robert W. Hart, MD

Abstract

Objective: Determine whether CPAP pressure requirements change during the first six months following bariatric surgery.

Methods:

Bariatric surgery patients diagnosed with obstructive sleep apnea (OSA) were placed on Autoset therapy before surgery and were seen at 2-weeks, 3-months and 6-months after surgery. Compliance and pressure data were obtained at each time point and weight was recorded.

Results: Data were analyzed with repeated measures ANOVA using weight loss as a covariate and Tukey’s HSD for post hoc comparisons. A main effect for the 95^th pressure centile (P95) and median pressure (PMed) were observed. The mean P95 decreased from 11.4 cm H₂O pre-operatively to 9.5 cm H₂O 2-weeks after surgery (95% CI 0.3–3.9). The PMed decreased from 8.8 cm H₂O pre-operatively to 6.9 cm H₂O 2-weeks after surgery (95% CI 0.4–4.1) and to 6.2 cm H₂O at 3-months (95% CI 0.3–6.7). A trend was observed for a decrease in the maximum pressure over time (p=0.07). A main effect for weight loss was not observed.

Conclusions: Reduction in optimal CPAP pressure (P95) was observed 2 weeks after surgery and remained stable at 3-months and 6-months. The PMed was significantly lower at 2-weeks and 3-months, whereas no change in PMax was observed. Pressure changes were independent of weight loss. Rapid weight loss and changes in hormonal regulation of weight and metabolism may be responsible for the pressure reductions. Self-adjusting CPAP offers advantages over fixed pressure therapy by compensating for changes in optimal pressure requirements following surgery.

Introduction

Obesity and obstructive sleep apnea (OSA) are prevalent and are associated with significant cardiovascular morbidity.¹ Greater than 50% of American adults are overweight with nearly one quarter of those overweight obese (BMI = 30 kg/m²).² Obesity itself is associated with decreased life expectancy and increased mortality.^3,4 The prevalence of OSA (AHI = 5) in the general population is estimated at 24% for men and 9% for women.^5,6 In the morbidly obese (BMI = 40 kg/m2), nearly 100% of men and 60–70% of women have OSA.^6,7 Bariatric surgery is an intervention for morbid obesity that results in dramatic weight loss and improvement or resolution of medical co-morbidities, such as diabetes, hypertension and hyperlipidemia.^8,9 Within the first post-operative week, patients with adult onset diabetes mellitus (NIDDM) show improvement in glycemic control.⁹ Several studies have shown improvement or resolution of OSA following surgically induced weight loss.^10–14

Unrecognized and untreated OSA can impact the bariatric surgery patient peri-operatively and throughout the weight loss period. Obesity itself predisposes to hypoxemia following surgery, and anesthesia and narcotic analgesics exacerbate pre-existing OSA and further contribute to hypoxemic burden.^15–17 Increased length of stay and serious post-operative complications following knee or hip replacement surgery are seen in patients with unrecognized or untreated OSA, compared to those with treated OSA or those without OSA.¹⁸

The greatest degree of relative weight loss occurs within the first 6 months after surgery; final weight is achieved within two years.^19,20 Following surgery, OSA may improve or resolve, but the apnea/hypopnea index (AHI) does not normalize in all patients. Even after substantial weight loss one year after surgery, as many as 54% of patients continued to have OSA that warranted intervention with CPAP.¹¹ A significant reduction in AHI may be seen after surgery, only to increase without concomitant weight gain years later.²¹

Weight loss following bariatric surgery alters CPAP pressure requirements. Lankford and colleagues²⁴ evaluated 15 bariatric surgery patients post-operatively with the Autoset Spirit to determine the optimal pressure as measured by the 95^th pressure centile (P95). This is the pressure which is not exceeded 5% of the night, and which is equivalent to the effective pressure obtained during manual laboratory titration.^22,23 Lankford’s patients were able to lower their fixed pressure prescriptions by an average of 18%.²⁴ Guardiano et al. reported that 3/8 (37.5%) of bariatric surgery patients who continued to have OSA at their goal weight required lower CPAP pressures.10 These studies examined changes in CPAP requirements at only one time point following bariatric surgery, typically 6 months or more after surgery and often at final weight. Inferential statistics were not reported in those studies.

Patients in the present study were prescribed self-adjusting CPAP (Autoset Spirit, ResMed, San Diego, CA) to compensate for pressure requirements that accompany weight loss. The Autoset Spirit (Autoset) self-adjusts to provide the minimum pressure at each time point during treatment to eliminate apneas, hypopneas and upper airway resistance, while preserving sleep architecture and continuity.^25,26 The device provides statistics regarding pressure requirements during treatment, and patient use and efficacy data. The current study was designed to explore how CPAP pressure requirements changed during the first 6 months after bariatric surgery, and determine how those changes were related to weight loss.

Methods

Subjects

Eligible patients were = 18 years of age with a BMI = 40 kg/m² who were being evaluated for Roux-en-Y gastric bypass surgery. Patients had not received prior surgical intervention for weight loss and were CPAP naive. Institutional review board approval and written informed consent were obtained.

Study Design

This was a prospective study. Per our institution’s protocol, patients seen pre-operatively by our practice for pulmonary and sleep clearance prior to surgery were invited to participate; patients were not necessarily seeking therapy for symptomatic OSA. At the initial visit, demographic and anthropometric data were recorded and patients completed the Epworth Sleepiness Scale (ESS). At the time of consent, patients were told that if they were diagnosed with OSA, they would need to use Autoset for at least 18 months after surgery, or until weight loss equaled or exceeded 70% of excess body weight.

Patients were scheduled for comprehensive laboratory based polysomnography before surgery. Outcome measures included the AHI and the oxygen desaturation index (ODI). Desaturations were defined as a drop in oxyhemoglobin saturation of >3%. An obstructive apnea was defined as cessation of airflow (airflow tracing between 0% and 20% of baseline) for =10 sec, accompanied by a desaturation. A hypopnea was defined as above, except that airflow tracing was between 20 and 50% of baseline. Clinically significant OSA requiring intervention was defined as an overall AHI =15 or a REM AHI =15. A REM stage marker of OSA severity was included to capture patients in whom OSA showed marked worsening or was seen exclusively during REM sleep.

Patients received either a full night diagnostic study followed by a full night CPAP titration, or a split-night study was performed according to AASM guidelines.²⁷ Patients diagnosed with OSA were titrated manually in the laboratory by a skilled technician. The pressure was started at 4 cm H₂O and increased in 1 cm increments to eliminate apneas, hypopneas and snoring. Effective pressure was defined as the fixed CPAP pressure that eliminated apneas, hypopneas, snoring and hypoxemia. Patients successfully titrated with fixed pressure CPAP in the laboratory were subsequently initiated on Autoset therapy at home with a range of 4–20 cm H₂O. Patients were instructed to use Autoset on a daily basis, including during their hospital stay.

Patients were seen for an office visit 2 weeks after surgery, and again at 3-months and 6-months after surgery. At each visit weight was obtained. Compliance and pressure data were downloaded from the Autoset device using compliance software (AutoScan 5.4; ResMed). Actual use per 24 hour period was recorded; a pressure transducer recorded use only when the patient was breathing with the mask in place. Regular use was defined as mask on time =4 hrs/night for =70% of nights used.²⁸ For each time point, pressure data was averaged for the 3 nights preceding the office visit, provided that use was =4 hrs for at least 2 of the 3 nights and leak values were within acceptable limits.

Statistical Analyses

Data are presented as mean ± SD. Changes in CPAP pressure over time were analyzed with repeated measures ANOVA using weight as a covariate. Significant main effects were followed with Tukey’s HSD post hoc comparisons. All analyses were performed using JMP 5.1.2 (SAS Institute, Cary, NC).

Results

Patient Characteristics

Patients accepted therapy by agreeing to a home visit from a respiratory therapist for Autoset delivery and instruction. Twenty-five women and six men (n=31) diagnosed with OSA used Autoset regularly until the first follow-up visit at 2-weeks post surgery. Six women and two men (n=8) continued as regular users for the entire follow-up period of 6 months. There were no differences in AHI, ODI, ESS, BMI, gender or weight loss at 2-week follow-up between the 23 patients who stopped using Autoset regularly 2 weeks after surgery and the 8 patients who remained regular users for 6 months (all p-values = 0.58). The 8 patients who continued with therapy were younger (mean age 43 vs. 50, p=0.03).

The mean age for the 8 patients was 43 ± 9, range 29–55 yrs. Mean weight was 161 ± 27 kg, range 118.2 to 201.8 kg. The mean BMI was 57.5 ± 12 kg/m², range 47.6 to 81.3 kg/m². The mean ESS score was 11.9 ± 7.4, range 4–22. Six of the 8 patients (75%) had either hypertension (HTN) and/or NIDDM, and were being treated pharmacologically for these conditions. Patients 1 and 4 discontinued antihypertensive medication at the post-op visit; all other patients were maintained on the same pharmacological agents during the 6 months. Patient characteristics are presented in Table 1. The adherence rate for regular Autoset use 6 months after surgery was 26%.

Diagnostic and Treatment Parameters

The mean AHI was 54.6 ± 48, range 11 to 130.8. Patient #2 had an overall AHI of 11 and a REM AHI of 62. The mean ODI was 51.3 ± 40.6, range 14.8 to 121.9. Substantial hypoxemic burden was observed during NREM and/or REM sleep in all patients. Percent of time with oxygen saturation levels below 90% in either NREM or REM sleep was =16.6%. The optimal CPAP pressure determined by manual laboratory titration ranged from 7 to 15, mean pressure 10.5 ± 2.6. These data are presented in Table 2.

Pressure Requirements and Weight Change

The mean value for PMax, P95 and PMed were calculated at each time point using the previous 3 nights’ data. Paired sample t-tests were used to compare PMax, P95 and PMed from pre-surgery to 2-weeks post-surgery in the sample of 31 patients who remained regular users for the first assessment at 2-weeks. Significant decreases were observed for all variables. The PMax decreased from 12.8 to 10.8 (CI 1.1–3.0, p < 0.0001), the P95 from 11.4 to 9.8 (CI 0.8–2.5, p=0.0001) and the PMed from 8.8 to 7.3 (CI 0.6–2.2, p=0.0004).

Repeated measures ANOVA with weight as a covariate was used to compare changes in PMax, P95 and PMed over time for the 8 patients who remained compliant at 6 months. A main effect for time was observed for P95 (F=3.9, p=0.02) and PMed (F=5.0, p=0.009), and a trend was seen for PMax (F=2.7, p=0.07). There was a significant decrease in the P95 from pre-Surgery to two weeks post-surgery (11.4 to 9.5 cm H₂O; 95% CI 0.3–3.9). The PMed decreased significantly from pre-surgery to two weeks post surgery (8.8 to 6.9 cm H₂O; 95% CI 0.4–4.1), and from pre-surgery to 3-months post-surgery (8.8 to 6.2 cm H2O; 95% CI 0.3 – 6.6). Two weeks after surgery, patients lost an average of 9.0 kg (range 4.1–15.5). Three months after surgery weight loss averaged 23 kg (range 14.5–33.2) and at 6 months average weight loss was 39.4 kg (range 29.4–48.2). A main effect for weight loss was not observed. Pressure requirements and weight changes for individual patients are presented in Table 3. Figure 1 illustrates these pressure changes over time.

Discussion

This is the first study to systematically examine CPAP pressure changes during the first 6 months after bariatric surgery. Significant decreases in Pmax, P95 and Pmed were observed in 31 patients who were regular Autoset users 2 weeks after surgery. Eight of those 31 patients continued to be regular users for 6 months following surgery. In that group of 8, changes in optimal pressure (P95) were seen two weeks post-surgery. Optimal pressure remained stable at 3-months and 6-months. The median pressure was lower at 2-weeks and at 3-months after surgery compared to pre-surgery values. A trend was observed for maximum pressure. Weight was used as a covariate in the analyses to determine how pressure requirements changed as a function of weight loss. A main effect for weight loss was not observed, suggesting that CPAP pressure changed independent of weight.

The observation that CPAP pressures decreased with modest weight reduction was not anticipated. Previous studies demonstrated lower CPAP pressure requirements following substantial weight loss.^24,29 Observations in those studies were made at varying time points following surgery, ranging from 6 months to over 2 years. In the present study, optimal pressure decreased within weeks after surgery and remained stable at 6 months. It is possible that a further decrease in pressure would be observed with additional weight loss and perhaps at final weight. Patients in the Lankford study lost an average of 44.6 kg (range 19.1–88.6) at the time of evaluation, but most patients remained obese (BMI = 30 kg/m²). One patient required an optimal pressure < 5 cm H₂O (BMI < 30 kg/m²), which likely indicates a mild degree or an absence of sleep-disordered breathing. Over 50% of patients in the Lankford study (8/15) required an optimal pressure =10 cm H₂O. The average weight loss at 6 months in the current investigation was 39.4 kg, and none of the patients had a BMI < 30 kg/m2.

The immediate change in optimal CPAP pressure may be explained by rapid weight loss and changes in hormone levels that regulate weight and metabolism. At 2 weeks post-surgery, patients had lost an average of 9.0 kg or nearly 6% of their body weight. Anthropometric measures and AHI may account for up to 76% of the variance in the CPAP pressure required to abolish OSA.³⁰ Using the prediction equation CPAP pressure = -5.12 + 0.13(BMI) + 0.16(Neck) + 0.04(AHI), the predicted change in CPAP pressure in the present sample would be a decrease of 0.5 cm H₂O 2 weeks after surgery. At 3 months the predicted change would be 1.4 cm H₂O and at 6 months 2.5 cm H₂O. The actual mean drop in P95 at 2-weeks post surgery was 1.9 cm H2O, close to a value intermediate to 3- and 6-months if one considered only the change in BMI and neck circumference. A similar prediction equation using BMI and AHI, but not neck circumference [(CPAP pressure = 0.52 + 0.174(BMI) + 0.042(AHI)], produ ced an even smaller reduction in P95 at each time point.³¹ Rapid initial weight loss may have altered fat deposition in the vicinity of the upper airway, accounting for a small portion of the variance in P95 and PMed.

Hormonal regulation of weight and metabolism may have accounted for a larger portion of the variance in CPAP pressure changes. Within weeks after surgery there is a significant decrease in blood glucose, insulin and leptin in bariatric surgery patients with and without NIDDM.³² The AHI is independently associated with these hormones after controlling for obesity and other risk factors.^33,34 Treatment with CPAP produces a decrease in leptin that is observed within the first week.^35,36 Furthermore, patients with effectively treated OSA, defined as an AHI less than 5, show a reduction in leptin, whereas patients on therapy but with incomplete control of OSA (AHI > 5) show no change in leptin.³³ If OSA represents a metabolic disorder involving regulation of breathing during sleep, then endocrine changes may act on respiratory control mechanisms. Immediate and dramatic changes in hormone levels, coupled with rapid weight loss, may alter upper airway collapsibility. The result is a lower CPAP pressure required to maintain upper airway patency.

The change in CPAP pressure shortly after surgery does not necessarily reflect a significant or clinically relevant decrease in the AHI. In a sample of 14 patients studied pre-opreatively and at 4.5 months after surgery, the AHI decreased from a mean of 40 to 11 events/hr. The BMI in those patients decreased from 45 to 33 kg/m².²¹ In a sample of 11 patients re-evaluated between 3–21 months after surgery, the AHI decreased from a mean of 56 events/hr pre-operatively to 23 events/hr. Two thirds of the patients in that sample still had moderate OSA, and most patients remained morbidly obese.13 Although not systematically evaluated, it appears that patients who continue to exhibit moderate OSA are those with a higher BMI.11,13,21 Patients remain at risk for cardiovascular morbidity if OSA is left untreated.

This is the first study to report CPAP compliance in a population of bariatric surgery patients. The adherence rate of 26% at 6 months is considerably lower than what is typically reported for other populations of CPAP users.²⁸ Bariatric surgery patients represent a unique group with many barriers to CPAP compliance. These patients may have been symptomatic for OSA, but were not seeking treatment for their sleep disorder. Instead, the sleep evaluation was one component of a thorough diagnostic work up prior to surgery. Many patients perceive the diagnosis of OSA to be irrelevant and without consequence. Patients are not motivated to adhere to a treatment that is perceived as temporary since many of them believe weight loss will cure OSA. Patients may accept CPAP therapy to comply with the requirements of pre-surgery evaluation, but abandon therapy prematurely. Another factor contributing to the low adherence rate may be the marked improvement in quality of life that occurs within weeks after surgery; patients reported less depression, greater self-esteem, more energy and an improvement in overall health.³⁷ Medical co-morbidities were not reported in that quality of life study, so it is not known if any patients had been diagnosed with OSA or were on CPAP therapy. A dramatic improvement in quality of life shortly after surgery may influence a patient’s decision to abandon CPAP therapy.

Patients in this study received extensive education regarding the diagnosis and treatment of OSA and the importance of Autoset use during weight loss. All polysomnograms were performed at an AASM-accredited hospital based sleep laboratory with a skilled technician in attendance. Respiratory therapists with extensive clinical experience reviewed Autoset use instructions with all patients during home set up. Despite intensive educational efforts, only a small percentage of patients used Autoset regularly for 6 months after surgery. This highlights the difficult task of treating OSA in this patient population. Physicians and surgeons need to emphasize the importance of treating OSA post-operatively and the associated risks of non-compliance with therapy. Bariatric surgery will not cure OSA in all patients. A post-operative polysomnogram is required to re-assess OSA severity.

The primary limitation of this study was the small sample size. An important assumption of inferential statistics is that the sample be representative of the population. The changes in PMax, P95 and PMed seen at 2-weeks for the larger group of 31 patients were similar in magnitude and absolute value to the subset of 8 patients that remained compliant for 6 months. The 23 patients who became irregular users or who abandoned treatment after 2-weeks were compared to the 8 compliant patients. The patients who remained compliant were younger, but the two groups did not differ on BMI, AHI, ODI, gender or the amount of weight loss at 2-weeks. Further support for the use of inferential statistics and repeated measures ANOVA is provided by an examination of the plot of the residuals, which shows a random distribution. This indicates that the model fits the data well. An important assumption for a repeated measures design is homogeneity of variance, which was confirmed with Levene’s test. These points justify the use of a repeated measures design to explore how CPAP pressures changed over time with weight loss.

Another potential limitation of the study was that we did not assess metabolic function, nor did we assess OSA severity after modest weight reduction. The study was designed to permit statistical evaluation of changes in weight loss and CPAP over time, which previously have not been reported. Analysis of insulin and leptin levels were not part of the research protocol, nor was it part of routine clinical evaluation. Follow-up polysomnography was scheduled to occur when the patient had lost 70% or more of excess body weight or after 18 months. A reassessment of OSA severity several weeks after surgery may have demonstrated a modest reduction in the AHI, but it probably would not have been statistically significant or clinically relevant. The degree of sleep-disordered breathing and hypoxemia would still be severe enough to warrant continued intervention with CPAP.

Self-adjusting CPAP was chosen over fixed pressure therapy for several reasons. First, the purpose of this study was to obtain pressure settings at several time points following surgery. It is highly unlikely that bariatric surgery patients would consent to several additional laboratory titration studies. Second, additional laboratory studies would be cost-prohibitive. Third, fixed time points would not permit examination of trends and patterns in pressure changes. Fourth, averaged data for several days’ use at home would provide a more representative sample of pressure requirements compared to a single night in the laboratory.

Future research will need to replicate and extend the findings of this study to a larger sample of bariatric surgery patients who remain compliant with therapy. Improving CPAP adherence in bariatric surgery patients will require intensive educational efforts directed at both physicians and patients regarding the high prevalence of OSA in morbid obesity. Aggressive efforts should continue at identifying and treating those patients with a high BMI who are at risk for OSA long before the pre-surgical evaluation. Bariatric surgery does not cure OSA in all patients, and continued use of CPAP may be needed.

Acknowledgments

This study was funded by a grant from the ResMed Foundation.The authors wish to thank Health Management, Inc. for their support.

References

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I have been active in sleep for the past 15 years, and I am excited to see the explosive growth in activity and the recognition that sleep medicine has achieved over this period. Indeed, there are very few examples in medicine that showed such a move from a curiosity item hailed by some researchers, into a well-accepted and active medical specialty. Still, in at least one aspect, I believe sleep medicine is still in its infancy stage.

Some years ago I invented the SleepStrip – the disposable sleep apnea screening device. It is a very simple device, nothing more than three thermistors and a miniature processor that analyzes breathing in real time, counts apnea and hypopnea events and reports the estimated AHI in the morning. During R&D, and after the device was launched, we were testing and validating the device’s accuracy by comparing its readings to AHI derived from full-scale, in-lab, same-night recordings, and this is when we began to see awkward things.

The same device, tested in different labs across the globe, received highly variable reviews. In some labs correlation with the sleep lab results was excellent, and in others – poor. Sensitivity, specificity and total accuracy were similarly inconsistent. As more and more studies were completed and published, the picture and the question that it presented became very clear: How can the same device, when tested against the gold standard, show such wildly different results? I have been thinking about this for several years now, and cannot escape the unavoidable conclusion: Not all sleep labs are created equal.

I am an engineer for the sleep sensor manufacturer SleepSense. I design sleep sensors for a living, performing activities such as calculating airflow patterns over a sensor and simulating the dynamics of chest movements when a person breathes. As part of the design process I consider many highly technical parameters that impact the signal the sensor will eventually produce in different circumstances. Knowing what I know about sensors and signal processing, it is easy to put a finger to at least a few of the variables people usually neglect when selecting sensors and sleep testing systems, or when scoring a study.

Ask yourself: What is the time constant of your pulse oximeter? Are you aware of the fact that different processing algorithms and time behaviors of the oximeter can greatly affect your study results? As an engineer, I think it is about time the experts took more interest in the tools they use and formulate standards for sensors and signal processing parameters that will, hopefully, make the sleep labs a little more “golden”. Not all wiggly lines are the same, and if sleep medicine is to mature into a science, it is time that we take a hard, long look at the tools of the trade and set standards.

Noam Hadas,
President and CEO,
SLP Inc, St Charles, IL

Adverse outcomes have been reported in the perioperative setting in patients with known or unrecognized obstructive sleep apnea syndrome (OSAS). Although epidemiologic data report a prevalence of OSAS at about 5%,¹ patients presenting to surgery have an estimated prevalence of 1–9%, or even higher in certain surgical categories.² Ashton et al. studied 1487 men older than 40 years undergoing non-cardiac surgery for risk of perioperative myocardial infarctions (MI) and surprisingly did not report a single case of obstructive sleep apnea. Assuming the lowest reported prevalence of 1%, at least 15 patients in this large series of patients could have had OSAS prior to the surgical intervention.³ This leaves open the possibility that some of these patients who had perioperative MIs had unrecognized OSAS. In a cross-sectional study of 170 consecutive patients presenting for bariatric surgery the prevalence of OSA in the severely obese group (BMI 35–39.9) was 83.3% and 73.6% of patients in the morbidly obese (BMI 40–49.9%) category.⁴ Another study evaluating 40 consecutive patients for bariatric surgery reported an obstructive sleep-related breathing disorder in 88% by polysomnography, 71% had OSA and majority of the patients were women with mean BMI of 47kg/m².⁵

Sleep studies in patients undergoing major abdominal surgery and cardiac surgery have shown suppression of rapid eye movement (REM) and slow wave sleep (SWS) after surgery.^6,7,8,9 The REM sleep returns or rebounds in the late postoperative period (when oxygen may have been discontinued) and has been linked to significant respiratory abnormalities in a group of elderly patients who underwent abdominal vascular surgery.¹⁰ In REM sleep, the neural drive to the pharyngeal muscles is at a minimum and the atonia of antigravity muscles predisposes to airway instability causing episodic hypoxemias.¹¹ Reduction in REM sleep, SWS and the lack of inherent rhythmicity are more pronounced after major surgery than after minor surgery even and less after laparoscopic surgery. 9 sedatives or analgesics, as well as the residual effects of anesthetic agents may worsen OSAS by decreasing pharyngeal tone and thereby increase upper airway resistance as well as attenuate the ventilatory and arousal responses to hypoxia, hypercarbia and obstruction.¹²

There is a limited amount of data that has focused specifically on OSAS and its impact on postoperative outcomes. In patients undergoing hip and knee replacement, up to one-third of those with OSAS developed substantial respiratory or cardiac complications including arrhythmias, myocardial ischemia, unplanned ICU transfers and reintubation.¹³ In another small prospective study evaluating the incidence of arrhythmia in patients with OSAS undergoing coronary artery bypass surgery, those with an oxygen desaturation index (ODI- defined as the number of desaturations = 4% per hour) = 5 had a relative risk of 2.8 for the development of atrial fibrillation postoperatively.¹⁴ In our own recent retrospective series of 25,587 patients that underwent cardiac surgery, 37 were confirmed to have sleep apnea by polysomnography.¹⁵ Higher incidence of encephalopathy (p=0.008), postoperative infection (0.028) and increased ICU length of stay (p=0.031) were noted in the group with OSAS after cardiac surgery. The difference in the rates of infection was mostly accounted for by the presence of mediastinitis (8.1% vs 1.6%). Differences in the rates of reintubation, tube time, and overall postoperative morbidity were not statistically significant.

Challenges in addressing the relative impact of OSAS on perioperative outcomes begin often times with the difficulty in diagnosing OSAS in the first place. The symptomatology of sleep apnea may be difficult to distinguish from normal variations in sleep behavior. Clinical examination at best carries a diagnostic sensitivity and specificity of only 50–60% for sleep apnea, when performed by experienced sleep physicians.16 Physical examination may reveal characteristic stigmata of OSAS including short thick neck, nasal obstruction, tonsillar hypertrophy, retrognathia and obesity. The degree of difficulty in visualizing the faucial pillars, soft palate and the base of the uvula can predict difficulty with intubation and should increase the suspicion of OSAS.17 In patients with these findings and history of daytime somnolence, snoring, and observed apneas, a presumptive diagnosis of OSAS can be made in the absence of a sleep study. Since the severity of these historical items correlates with the severity of sleep study-proven OSAS, use of a simple screening questionnaire for OSAS appears reasonable. However, none have so far been validated for use in the preoperative setting. Some studies suggest routine overnight polysomnography in all patients undergoing bariatric surgery regardless of BMI.5 Clinical suspicion for sleep apnea may also arise intra-operatively in some patients. Airway obstruction out of proportion to the apparent degree of sedation, pronounced tendency for upper airway obstruction during or upon recovery from anesthesia can suggest sleep apnea that has not been recognized perioperatively.18

Data guiding perioperative management of patients with known sleep apnea or those suspected of having this condition is limited. Increased awareness for close monitoring of high risk patients is recommended. For patients with OSAS having abdominal or other major surgery, significant expected pain or opioid requirement, severe OSAS at baseline needing CPAP at home, or with observed obstruction or episodic desaturations evident in recovery room continued inpatient monitoring is advised after the patient is moved out of PACU.19 Routine ICU admission after surgery may not be necessary except in patients with co-existing cardiopulmonary disease or difficult airway. Patients at increased perioperative risk from OSAS should be extubated while awake and after full reversal of neuromuscular blockade is verified. Benzodiazepines should be avoided altogether and narcotics limited. Alternative forms of analgesia, such as non-steroidal antiflammatory medications, nerve blocks or local analgesics should be considered. If narcotics are required for pain control, patients should be in a monitored setting. Patient controlled analgesia with no basal rate may help limit dosing.20 General anesthesia with a secure airway is preferable to deep sedation without a secure airway, particularly for procedures that may mechanically compromise the airway. Respiratory arrest has been reported in those with OSAS receiving epidural opioids at 2 to 3 days postoperatively.21 If neuraxial analgesia is planned, local anesthetics alone should be preferred over opioids in combination. Case series and limited data suggest that use of CPAP in the perioperative setting for known cases of OSAS may help reduce postoperative complications. Until additional information is available to guide decision making, screening for OSAS should be incorporated as part of the preoperative assessment of patients subjected to surgery.

Roop Kaw, MD,
Assistant Professor of Medicine,
Section of Hospital and Perioperative Medicine,
Cleveland Clinic Foundation, Cleveland, OH

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