Sleep Apnea Severity Classification — Revisited

Extract

As I read Ho et al.,1 I was abruptly reminded of a dilemma that our field of sleep medicine has failed to clarify: the relationship between the apnea-hypopnea index (AHI) and the severity categorization of sleep-disordered breathing (SDB). As polysomnogram (PSG) scoring criteria have changed over time, severity classification categories have remained constant. These authors make it blatantly clear that the AHI can vary widely with the use of different hypopnea scoring criteria. In this study, the original Sleep Heart Health Study PSGs were re-scored using three hypopnea definitions: “decrease in airflow or chest wall or abdominal excursion greater than 30% from baseline, but not meeting apnea definitions associated with either: (1) a 4% or greater fall in oxyhemoglobin saturation; (2) a 3% or greater fall in oxyhemoglobin saturation; or (3) a 3% or greater fall in oxyhemoglobin saturation or an event-related arousal.” They investigated the change in SDB severity classification that occurred with the change in AHI. The severity classifications used were: mild (AHI = 5–14), moderate (AHI = 15–30), and severe (AHI > 30).² From the 1999 “conservative” hypopnea scoring criteria, > 4% oxyhemoglobin desaturation,² to the new, “liberal” definition, > 3% oxyhemoglobin desaturation or an event-related arousal,^3,,4 there was a dramatic increase in the AHI and SDB severity in this representative “normal” US population. The prevalence of those with a combined moderate + severe sleep apnea increased from 22% to 45% and the prevalence of those having a normal PSG (AHI < 5 events/h) decreased from 48% to 17% with use of the “liberalized” scoring criteria. It would seem logical that as AHI increases with use of the “liberal” hypopnea scoring criteria, the SDB severity classification also should be modified.