What are respiratory events during sleep?
- Respiratory events are apnea, hypopnea, and respiratory effort–related arousal (RERA). An apneic episode is an airflow decrease of at least 90% from baseline lasting at least 10 seconds (try holding your own breath for 10 seconds!).
- Hypopnea is defined as 10 seconds of at least a 30% decrease in airflow, resulting in ≥ 4% desaturation on pulse oximetry. RERA criteria should be sought if an observed event does not meet apnea or hypopnea criteria. RERA is defined as a sequence of breaths > 10 seconds in duration associated with increased respiratory effort and results in an arousal from sleep.
- The American Academy of Sleep Medicine (AASM) directs that apnea, hypopnea, and RERA, if present, be scored in the routine PSG interpretation.
- The average number of apnea and hypopnea episodes in 1 hour is referred to as the apnea–hypopnea index (AHI). However, if RERA is present, then the average number of apnea, hypopnea, and RERA should be calculated.
- This is the respiratory disturbance index (RDI). Note that the AHI does not equal the RDI, even though the terms are sometimes used interchangeably; such an interchange could create confusion.
