Exclusion of EEG-based Arousals in Wake Epochs of Polysomnography Leads to Underestimation of the Arousal Index.

Study Objectives: There is an internal contradiction in current American Academy of Sleep Medicine standards for arousal index (AI) calculation in polysomnography: Arousals in sleep and wake epochs are counted, but only sleep time is used in the denominator. This study aimed to investigate the impact of including arousals scored in wake epochs on the AI. Methods: We compared AIs including (AI(in)(c)) vs excluding (AI(exc)) awake-epoch arousals from 100 consecutive polysomnograms conducted for investigation of possible obstructive sleep apnea. To determine the AI that most closely approximated "truth," and AI(exc) were compared to an Al calculated from continuous sleep analysis (AI(cont)) in a 20-polysomnogram subgroup of patients. Results: The median (interquartile range) increase in AI(inc) was 5.2 events/h (3.5-8.1) vs AI(exc) = 28.0 events/h [18.4-38.9] vs AI(exc) = 22.9 events/h [13.1-31.3]), equating to an increase of 25.3% (15.6-40.8). As the Al increased, the difference increased (P < .001), with decreasing sleep efficiency and an increasing apnea-hypopnea index as the strongest predictors of the difference between AI(exc) and The absolute AI(exc)-AI(cont) difference (7.7 events/ h [5.1-13.6]) was significantly greater than the AI(exc)-AI(cont) difference (1.2 events/h [0.6-5.7]; z = -3.099; P = .002). Conclusions: There was a notable increase in AI when we included wake-epoch arousals, particularly in patients with more severe obstructive sleep apnea or reduced sleep efficiency. However, the AI including wake-epoch arousals best matched the "true" continuous sleep-scoring AI. Our study informs clinical and research practice, highlights epoch scoring pitfalls, and supports the current American Academy of Sleep Medicine standard arousal reporting approach for future standards.