13: OXYGENATION INDEX TRACKS CLINICAL OUTCOMES AND BIOMARKERS BETTER THAN PAO2/FIO2 IN ADULTS WITH ARDS

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Introduction: The ratio of arterial oxygen partial pressure to fractional inspired oxygen (PF, mmHg) is used to grade acute respiratory distress syndrome (ARDS) severity in adults, but does not account for airway pressure. Oxygenation index (OI: mean airway pressure/PF, cmH2O/mmHg) is used in pediatric ARDS but not in adults. We hypothesize that OI better correlates with clinical outcomes and biomarkers than PF in adults with ARDS on invasive mechanical ventilation (IMV). Methods: A cohort of adult patients with ARDS on IMV who had been prospectively enrolled from 2 hospitals between 2020-2024 were included. All patients had clinical phenotyping and a subset had serologic ARDS biomarkers. Hourly OI and PF were obtained from the medical record and the 24-hour mean of each index on days 1 and 2 was recorded. Associations between the daily mean of respiratory indices (OI, PF) and two clinical outcomes (90-day mortality, number of ventilator free days at 14 days [VFD14]) and between respiratory indices and two ARDS biomarker concentrations (RAGE, S-PD) were assessed using regressions. A p-value < 0.05 defined statistical significance. Results: There were 145 patients (43% female; 60 [46,70] years) enrolled. On days 1 and 2, mean (SD) OI was 10.4 (2.9) and 9.7 (2.2), while PF was 162 (40) and 187 (42). Ninety-day mortality was 43%. Median (IQR) VFD14 was 4.1 (0,10.2) days. On day 1, OI and PF were not associated with 90-day mortality. On day 2, OI (OR: 1.08, p< 0.01) and PF (OR: 0.98, p=0.02) correlated with 90-day mortality and OI fit the data better than PF (Akaike information criteria: 166 vs 179, respectively; p< 0.01). The VFD14 correlated with OI and PF on both days, but OI explained twice the VFD14 variance as PF (Day 1: OI: r2=0.12, p< 0.01;PF: r2=0.07, p< 0.01. Day 2: OI: r2=0.21, p< 0.01;PF: r2=0.1, p< 0.01). Biomarkers were available for 21 patients. Concentrations of RAGE were correlated with OI (Day 1: r2=0.25, p=0.02; Day 2: r2=0.24, p=0.04) but not PF (Day 1: r2=0.07, p=0.25; Day 2: r2=0.08, p=0.22). Concentrations of S-PD were correlated with OI (Day 1: r2=0.38, p< 0.01; Day 2: r2=0.28, p=0.02) but not PF (Day 1: r2=0.07, p=0.24; Day 2: r2=0.11, p=0.15). Conclusions: In a multicenter cohort of adults with ARDS on IMV, OI correlated more closely with clinical outcomes and biomarkers than PF.

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