O042 Impact of supine REM AHI on diagnostic sleep studies for OSA

INTRODUCTION: A conventional belief is that REM exacerbates positional OSA (POSA). Subsequently, PSGs often report on presence of supine REM with the presumption that without supine REM, the AHI may be underestimated. This study explores the impact of REM upon obstructive respiratory events in sleep when supine. METHODS: From 1/1/2019 through 31/12/2020 PSGs for OSA diagnosis performed using Sleepware G3 were reviewed. A subgroup analysis was conducted within POSA patients defined as 1) total AHI>10/hour and non-supine AHI<10/hr, 2) supine AHI>2x non-supine AHI and 3) at least 15min of supine and non-supine sleep. Data was analysed with Pearson’s Chi Squared Test using Stata 16.1. RESULTS: Supine REM occurred in 97% of the 467 PSG’s. The supine REM AHI was 32.1(95%CI 29.1–35.2), compared to supine NREM AHI of 36.6(33.5–39.6), non-supine REM AHI of 21.3(18.8–23.9) and non-supine NREM AHI of 19.9(17.3–22.5). Among 109 POSA patients the supine REM AHI was 31.7(26.1–37.4) compared to 28.9(24.8–32.9) in supine NREM, 9.5(6.1–12.9) in non-supine REM and 3.5(3.0–4.0) in non-supine NREM. The average duration of obstructive respiratory events was 27.3 seconds (26.2–28.5) in REM compared to 23.5 seconds (22.8–24.2) in NREM. This statistically significant difference did not persist in POSA patients. DISCUSSION: The results do not support an additive effect of REM beyond supine positioning among patients with POSA, however there is evidence that REM lengthens respiratory events, which may reduce AHI. In the POSA subgroup analysis, there was an increased AHI in REM compared to NREM only in the non-supine position.