The impact of study type and sleep measurement on oxygen desaturation index calculation.

Abstract

The oxygen desaturation index (ODI) is an important measure of sleep disordered breathing during polysomnography (PSG) however the AASM Manual (V3) does not specify whether to include oxygen desaturations occurring during wake epochs. Additionally ODI obtained from PSG can differ from ODI using home sleep apnea tests (HSAT) that do not measure sleep, hampering diagnostic and treatment decision reliability. This study aimed to (1) compare an ODI that included all desaturations to an ODI that excluded desaturations occurring during wake epochs in PSG, and (2) compare ODIs obtained from PSG to HSAT. 100 consecutive PSGs for investigation of OSA were compared. ODIs were calculated including all desaturations (ODIall) and by excluding desaturations entirely during wake epochs (ODIsleep). Additionally, we compared ODIall to an ODI calculated using monitoring time as the denominator (ODIHSAT). The median (IQR) 3% ODI for ODIall was 22.8/h (13.1, 44.1) and ODIsleep was 17.6/h (11.5, 35.2)/h, (median difference: -3.9/h (-8.2, -.9); 21.0% (8.7, 33.2)). This discrepancy was larger with increasing ODI and decreasing sleep efficiency. The ODIHSAT was 17.4/hr (11.3, 35.2) and the median reduction in ODIHSAT versus ODIall was -4.5/h (-10.9, -2.0): (21.6% (11.1, 33.8)). ODI was significantly reduced when desaturations in wake epochs were excluded, and when ODI was based on monitoring time rather than sleep time, with potential for underestimation of disease severity. Results suggest that ODI can differ substantially depending on the calculation and study type used, and that there is a need for standardization to ensure consistent diagnosis and treatment outcomes.