Managing patients with acute respiratory distress syndrome (ARDS) requires frequent changes in mechanical ventilator respiratory settings to optimize arterial oxygenation assessed by arterial oxygen partial pressure (PaO₂) and saturation (SaO₂). Pulse oxymetry (SpO₂) has been suggested as a non-invasive surrogate for arterial oxygenation however its accuracy in COVID-19 patients is unknown. In this study, we aimed to investigate the influence of COVID-19 status on the association between SpO₂ and arterial oxygenation. We prospectively included patients with ARDS and compared COVID-19 to non-COVID-19 patients, regarding SpO₂ and concomitant arterial oxygenation (SaO₂ and PaO₂) measurements, and their association. Bias was defined as mean difference between SpO₂ and SaO₂ measurements. Occult hypoxemia was defined as a SpO₂ ≥ 92% while concomitant SaO₂ < 88%. Multiple linear regression models were built to account for confounders. We also assessed concordance between positive end-expiratory pressure (PEEP) trial-induced changes in SpO₂ and in arterial oxygenation. We included 55 patients, among them 26 (47%) with COVID-19. Overall, SpO₂ and SaO₂ measurements were correlated (r = 0.70; p < 0.0001), however less so in COVID-19 than in non-COVID-19 patients (r = 0.55, p < 0.0001 vs. r = 0.84, p < 0.0001, p = 0.002 for intergroup comparison). Bias was + 1.1%, greater in COVID-19 than in non-COVID-19 patients (2.0 vs. 0.3%; p = 0.02). In multivariate analysis, bias was associated with COVID-19 status (unstandardized β = 1.77, 95%CI = 0.38-3.15, p = 0.01), ethnic group and ARDS severity. Occult hypoxemia occurred in 5.5% of measurements (7.7% in COVID-19 patients vs. 3.4% in non-COVID-19 patients, p = 0.42). Concordance rate between PEEP trial-induced changes in SpO₂ and SaO₂ was 84%, however less so in COVID-19 than in non-COVID-19 patients (69% vs. 97%, respectively). Similar results were observed for PaO₂ regarding correlations, bias, and concordance with SpO₂ changes. In patients with ARDS, SpO₂ was associated with arterial oxygenation, but COVID-19 status significantly altered this association.

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