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The following is a summary of “Limitations of SpO2 /FiO2-ratio for classification and monitoring of acute respiratory distress syndrome—an observational cohort study,” published in the February 2025 issue of Critical Care by Erlebach et al.
The pulse-oximetric peripheral oxygen saturation to a fraction of inspired oxygen (SpO2 /FiO2) ratio has been suggested as an additional hypoxemia criterion in the new global acute respiratory distress syndrome (ARDS definition).
Researchers conducted a retrospective study to assess the clinical and theoretical limitations of the SpO2 /FiO2 ratio in classifying patients with ARDS and tracking disease progression.
They analyzed patients with ARDS from 3 high-resolution ICU databases: ICU Cockpit, Medical information mart for intensive care (MIMIC-IV) (Version 3.0). The salzburg intensive care database (SICdb) (Version 1.0.6). The ARDS cases were identified using the Berlin criteria or International classification of diseases (ICD-9/10) codes. Time-matched values for SpO2, Fi2, and partial pressure of oxygen in arterial blood (PaO2) were collected. Severity classification followed SpO2 /FiO2 and PaO2 /FiO2 thresholds from the newly proposed global ARDS definition.
The results showed that 708 patients with ARDS were analyzed, with SpO2 /FiO2 misclassifying ARDS severity in 33% of data points, 84% of which were categorized as more severe. This misclassification was partly due to SpO2 measurement imprecision and the equation converting SpO2 /FiO2 to PaO2 /FiO2. SpO2 /FiO2 showed high dependence on FiO2 settings, significantly impacting treatment effects and limiting its ability to track ARDS severity changes, which was achieved in fewer than 20% of events.
Investigators concluded that the interchangeability of SpO2 /FiO2 and PaO2 /FiO2 for ARDS severity classification and monitoring was limited due to its inadequate trending ability and high dependence on FiO2 settings.
Source: ccforum.biomedcentral.com/articles/10.1186/s13054-025-05317-7
