Heterogeneity of hypoxemia severity according to oxygenation index in COVID-19 pneumonia

Nunez, I.; Soto-Mota, A.

Objective: To compare hypoxemia severity of patients with COVID-19 pneumonia that arrive at an emergency department as classified by three oxygenation indexes. Design: Retrospective analysis of pulse oximeter saturation and arterial blood gas analysis obtained at arrival. Setting: Tertiary referral hospital in Mexico City converted early in the pandemic to a COVID-19 center. Patients and measurements: A total of 2,960 patients with suspected COVID-19 pneumonia were admitted to the emergency department from April 2020 until March 2021. Pulse oximeter saturation and arterial blood gas analysis was obtained in all of them. Pulse oximeter saturation (SpO2) to inspired oxygen fraction ratio (FiO2), oxygen saturation in arterial blood (SatO2) to FiO2 ratio, and oxygen pressure in arterial blood to FiO2 ratio were calculated for every patient. Interventions: None. Main Results: A strong correlation was seen between PaO2/FiO2 & SpO2/FiO2 (rho = 0.6, p < 0.001), and SatO2/FiO2 & SpO2/FiO2 (rho = 0.65, p < 0.001), while a very strong correlation was seen between PaO2/FiO2 & SatO2/FiO2 (rho = 0.88, p < 0.001). When classifying severity by quantiles, considerable cross-over was observed when comparing oxygenation indexes, as only 785 (26.5%) patients were in the same quintile across the three indexes. Conclusions: Hypoxemia severity is heterogeneous according to the oxygenation index utilized. This limits their usefulness as sole markers of severity, as inter-observer variability, especially on FiO2 estimation, and different practices limit consistent follow up and treatment decisions.