What Are Limitations Of Polysomnography As A Reference Standard

There are limitations to PSG implementation and interpretation. Sleep staging is reasonably well-standardized according to published rules (62) but these were developed before OSA was well-recognized. For example, arousals were not well-defined (62) and while there are subsequent published recommendations (14), there are no universally accepted or easily reproducible definitions, making inter-scorer reliability potentially poor between clinical centers.

Scoring of hypopneas is in evolution. Although research definitions have been proposed (13), the correlation between these definitions and clinical outcomes is essentially unknown at this time. This leads to difficulty in determining a threshold AHI to confirm OSA.

Night-to-night variability of the AHI or RDI can be substantial and is due to a number of factors, including body position and the amount of REM sleep (supine and REM AHIs are almost always higher than non-rapid eye movement [NREM] and lateral position AHIs). Although the mean AHI in a group of OSA patients does not change substantially, individual patients may have large increases or decreases (19). For this reason, more than one night of PSG may be necessary to clarify whether a patient has OSA. This variability also makes it difficult to know how much of the difference between a portable monitor and PSG result is normal variability and how much is from the limited set of monitored variables attended or unattended during sleep.

The use of a single AHI to characterize the entire night's study is simplistic. For example, the classification of OSA by overall AHI does not take into account a number of variables that may well have clinical relevance such as supine and REM AHIs and the degree of arterial oxygen desaturation.

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