Prognostic Accuracy of SpO₂-based Respiratory Sequential Organ Failure Assessment for Predicting In-hospital Mortality

Introduction: In this study we aimed to investigate the prognostic accuracy for predicting in-hospital mortality using respiratory Sequential Organ Failure Assessment (SOFA) scores by the conventional method of missing-value imputation with normal partial pressure of oxygen (PaO₂)- and oxygen saturation (SpO₂)-based estimation methods.

Methods: This was a single-center, retrospective cohort study of patients with suspected infection in the emergency department. The primary outcome was in-hospital mortality. We compared the area under the receiver operating characteristics curve (AUROC) and calibration results of the conventional method (normal value imputation for missing PaO₂) and six SpO₂-based methods: using methods A, B, PaO₂ is estimated by dividing SpO₂ by a scale; with methods C and D, PaO₂ was estimated by a mathematical model from a previous study; with methods E, F, respiratory SOFA scores was estimated by SpO₂ thresholds and respiratory support use; with methods A, C, E are SpO₂-based estimation for all PaO₂ values, while methods B, D, F use such estimation only for missing PaO₂ values.

Results: Among the 15,119 patients included in the study, the in-hospital mortality rate was 4.9%. The missing PaO₂was 56.0%. The calibration plots were similar among all methods. Each method yielded AUROCs that ranged from 0.735-0.772. The AUROC for the conventional method was 0.755 (95% confidence interval [CI] 0.736-0.773). The AUROC for method C (0.772; 95% CI 0.754-0.790) was higher than that of the conventional method, which was an SpO₂-based estimation for all PaO₂ values. The AUROC for total SOFA score from method E (0.815; 95% CI 0.800-0.831) was higher than that from the conventional method (0.806; 95% CI 0.790-0.822), in which respiratory SOFA was calculated by the predefined SpO₂ cut-offs and oxygen support.

Conclusion: In non-ICU settings, respiratory SOFA scores estimated by SpO₂ might have acceptable prognostic accuracy for predicting in-hospital mortality. Our results suggest that SpO₂-based respiratory SOFA score calculation might be an alternative for evaluating respiratory organ failure in the ED and clinical research settings.