P009 Impact of respiratory event timing and epoch scoring on AHI

Abstract Introduction During polysomnography (PSG) analysis sleep is scored in 30-second epochs and the apnoea-hypopnoea index (AHI) is a primary outcome measure. In current standards respiratory events beginning or ending in sleep epochs are included in the AHI. Alternative methods allow inclusion of events which start and end in wake epochs but span sleep epochs (ANZSSA/ASA recommendation), or only include events which start in sleep epochs. We aimed to quantify the impact of using three calculation methods for associating respiratory events with sleep on the AHI. Method Three AHIs were calculated from 112 diagnostic PSGs for obstructive sleep apnoea investigation, including respiratory events that: (1) started or ended in sleep epochs (AHI-AASM), (2) spanned sleep epochs (AHI-ANZSSA/ASA), or (3) started in sleep epochs (AHI-START). Results The median (IQR) AHI-AASM was 18.0 (6.9, 35.7), AHI-ANZSSA/ASA was 18.0 (7.1, 35.7), and AHI-START was 16.4 (6.6, 32.6). The median difference in AHI-START vs. AHI-AASM was -1.0 (-3.4, -0.3), [range -21.1 to 0.0], equating to a median decrease in AHI of 6.0% (2.3, 11.3). The median difference in AHI-ANZSSA/ASA vs. AHI-AASM was 0.0 (0.0, 0.2), [range 0.0 to 4.4]. Discussion When comparing to AHI calculated using current standards, where respiratory events can begin or end in sleep epochs, AHI was marginally reduced when limiting to events starting in sleep epochs. There was no difference when events spanning sleep epochs were included, despite the logical inclusion of respiratory events overlapping sleep but not starting and ending in sleep epochs. This investigation informs clinical practice, highlights epoch scoring difficulties, and informs future scoring standards.