What is the role of polysomnography (PSG) in the workup of sleep-disordered breathing (SDB)?

Updated: Feb 13, 2020
  • Author: Vittorio Rinaldi, MD; Chief Editor: Zab Mosenifar, MD, FACP, FCCP  more...
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Polysomnography (PSG) is the criterion standard diagnostic test for OSAS. A respiratory event suggestive of OSAS is defined as a decrease in nasal and oral airflow, alone or with thoracoabdominal movements, of more than 90% (apnea) or of more than 50% but less than 90% (hypopnea) that lasted for at least 10 seconds. A decrease in arterial oxygen saturation of 4% or more is considered significant oxygen desaturation. [46]

Information from PSG is reported in the form of the respiratory disturbance index (RDI; also referred to as the apnea-hypopnea index [AHI]). The RDI is the number of apneas or hypopneas 10 seconds or longer occurring per hour of sleep. A normal RDI is less than 5. An RDI less than or equal to 5 is suggestive of simple snoring with no OSAS. An RDI greater than 5 and less than or equal to 15 is suggestive of mild OSAS. An RDI greater than 15 and less than or equal to 30 is suggestive of moderate OSAS. Finally, an RDI greater than 30 is suggestive of severe OSAS.

The loudness and persistence of snoring (constant versus intermittent) are usually reported. Body position is also recorded so one can determine what position (usually supine) and in what sleep phase (usually rapid-eye-movement [REM] sleep, when muscle tone is most relaxed) the patient is in when respiratory events occur.

In-laboratory PSG is the criterion standard for diagnosing OSAS. However, PSG has several limitations, including the necessity of performing the test in a sleep laboratory, high costs, the considerable technical expertise required, and the long analyzing time needed by the operator. In addition, the examination often must be repeated because of the interference of monitoring electrodes with the physiologic sleep of the patient (“first night effect”). Therefore, timely access to PSG is often a problem.

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