Limitations of SpO2 / FiO2-ratio for classification and monitoring of acute respiratory distress syndrome—an observational cohort study
Rolf Erlebach, Una Pale, T. Beck, Saša Marković, Marko Seric, Sascha David, E. Keller
Abstract
Abstract Background The ratio of pulse-oximetric peripheral oxygen saturation to fraction of inspired oxygen (SpO 2 /FiO 2 ) has been proposed as additional hypoxemia criterion in a new global definition of acute respiratory distress syndrome (ARDS). This study aims to evaluate the clinical and theoretical limitations of the SpO 2 /FiO 2 -ratio when using it to classify patients with ARDS and to follow disease progression. Methods Observational cohort study of ARDS patients from three high-resolution Intensive Care Unit databases, including our own database ICU Cockpit, MIMIC-IV (Version 3.0) and SICdb (Version 1.0.6). Patients with ARDS were identified based on the Berlin criteria or ICD 9/10-codes. Time-matched datapoints of SpO 2 , FiO 2 and partial pressure of oxygen in arterial blood (PaO 2 ) were created. Severity classification followed the thresholds for SpO 2 /FiO 2 and PaO 2 /FiO 2 of the newly proposed global definition. Results Overall, 708 ARDS patients were included in the analysis. ARDS severity was misclassified by SpO 2 /FiO 2 in 33% of datapoints, out of which 84% were classified as more severe. This can be partially explained by imprecision of SpO 2 measurement and equation used to transform SpO 2 /FiO 2 to PaO 2 /FiO 2. A high dependence of SpO 2 /FiO 2 -ratio on FiO 2 settings was found, leading to major treatment effect and limited capability for tracking change in ARDS severity, which was achieved in less than 20% of events. Conclusions The use of SpO 2 /FiO 2 interchangeably with PaO 2 /FiO 2 for severity classification and monitoring of ARDS is limited by its inadequate trending ability and high dependence on FiO 2 settings, which may influence treatment decisions and patient selection in clinical trials.