Monitors


Setting the Parameters

by David Baker and Preetam Schramm, PhD, RPSGT

AASM recommendations for portable monitoring.

Revised portable monitoring (PM) device practice parameters were announced by the American Academy of Sleep Medicine (AASM), following systematic and extensive data evaluation by an AASM task force.1 Based on previous reviews,2,3 the paper identifies recommended practice parameters for the unattended use of PM devices to study adult patients with possible obstructive sleep apnea (OSA), ending a long-standing debate about the role of PM as a diagnostic tool for OSA. The AASM review contains a description of limitations applicable to the unattended use of PM devices, instances in which PM is not appropriate, technical considerations for PM, and testing recommendations.1

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The evidence used in the evaluation of PM devices was primarily based, among other factors, on the apnea-hypopnea index (AHI), the in-lab polysomnography (PSG) as the “gold” standard, and its use only to evaluate OSA. The limitation associated with the AHI was based on the commonly used but arbitrary use of AHI thresholds by insurance companies and the Centers for Medicare and Medicaid Services to identify patients with sleep apnea (ie, AHI = 15 events/hour).4 Establishing a set AHI of 15 may skew the comparison between the portable device and the gold standard PSG. The AHI may change from night to night depending on a variety of reasons (amount of REM, medication/alcohol consumption, amount of supine time, etc). For instance, a PSG may show an AHI for a patient of 17, and the same patient may have an AHI of 14 with the portable device. Using an AHI of 15 would show that this portable device failed.

Table 1. Approved populations for portable monitoring in conjunction with a comprehensive sleep evaluation and supervised by a sleep-boarded or board-eligible physician.

 

Of significance in this new recommendation by the AASM is the stance that unattended PM devices can be used as an acceptable alternative to PSG for the diagnosis of OSA in patients with a high pretest probability of moderate to severe OSA. PM may be used also as a pretest to PSG in patients with a high probability of moderate to severe OSA and indicated in patients who may have limited access to in-lab PSG due to immobility, safety, or critical illness. Another recommendation permits PM devices to be used to monitor non-CPAP response to oral appliances, upper airway surgery, and weight loss patients. All of the above recommendations are preempted by the condition that PM should be performed only in conjunction with a comprehensive sleep evaluation and must be supervised by a sleep-boarded or board-eligible physician (Table 1).

The Task Force also describes three instances in which PM is not appropriate for the diagnostic evaluation of suspected OSA. In cases of comorbidity with other sleep disorders (ie, central sleep apnea, periodic limb movement disorder, insomnia, parasomnias, circadian rhythm disorders, or narcolepsy); in cases of comorbidity with medical conditions (ie, moderate to severe pulmonary disease, neuromuscular disease, or congestive heart failure); and as a general screening tool among asymptomatic populations, the Task Force finds the use of PM inappropriate1 (Table 2).

Table 2. Populations not approved for portable monitoring.

 

Furthermore, the Task Force suggests that all sleep laboratories confirm that the commercial PM device to be used has specific studies documenting its performance and that the device has the necessary characteristics pertinent to the general category recommended (ie, Type 3). In the previous4 and current PM assessment,1 it is highly recommended that the interpreting physician review the raw data from the PM device. The device should also have the ability to allow manual scoring of the raw data. Scoring should be performed by trained and qualified technicians and the raw data reviewed by experienced physicians who are familiar with the PM devices. The guidelines also recommend PM be performed under the direction of an AASM-accredited sleep program.

Technical recommendations for PM devices were based on sensors used for the in-laboratory setting. The Task Force recommends the use of airflow, respiratory effort, and blood oxygen measurements for PM devices. The assessment was limited to Type 3 devices, which typically use a minimum of four channels and no electroencephalogram (EEG) recording.

Table 3. Recommended sensors for Type 3 PM devices.

 

Two sensors are recommended for simultaneous monitoring of airflow. The detection of apneas should be performed with an oronasal thermal sensor, and a nasal pressure transducer should be used for the detection of hypopneas. Respiratory effort can be monitored using esophageal manometry, or calibrated or uncalibrated respiratory inductance plethysmography, and blood oxygen should be monitored using pulse oximetry with a minimum averaging time of 3 seconds and accommodating motion artifact5 (Table 3).

The guideline-writing committee called for urgently needed research that addresses many of the gaps related to PM devices. Their recommendations for future research included obtaining data without using a fixed-threshold AHI, evidence from primary care populations, and verification in patients with comorbid conditions, nonwhites, and women. They further recommended that the data should include sufficient sample sizes in well-designed studies. The only PM class that could be currently designated for routine use in the attended setting with the limitations described above is Type 3.


David Baker is the president and CEO of Embla Systems, based in Denver. Preetam Schramm, PhD, RPSGT, is principal clinical specialist at Embla Inc, Denver. The authors can be reached at sleepeditor@nullallied360.com.

References

    1. Collop NA, Anderson WM, Boehlecke B, et al; Portable Monitoring Task Force of the American Academy of Sleep Medicine. Clinical guidelines for the use of portable monitors in the diagnosis of obstructive sleep apnea in adult patients. J Clin Sleep Med. 2007;3:737-747.
    2. Chesson AL, Ferber R, Fry J, et al. The indications for polysomnography and related procedures. Sleep. 1997;20:406-422.
    3. American Sleep Disorders Association Report. Standards of Practice Committee. Practice parameters for the use of portable recording in the assessment of obstructive sleep apnea. Sleep. 1994;17:372-377.
    4. Chesson Al, Berry RB, Pack A. Practice parameters for the use of portable monitoring devices in the investigation of suspected obstructive sleep apnea in adults. Sleep. 2003;26:907-913.
    5. Iber C, Ancoli-Israel S, Chesson AL, Quan S. The AASM Manual for the Scoring of Sleep and Associated Events: Rules, Terminology and Technical Specifications. Westchester, Ill: AASM; 2007.