Association Between Peripheral Blood Oxygen Saturation (SpO2)/Fraction of Inspired Oxygen (FiO2) Ratio Time at Risk and Hospital Mortality in Mechanically Ventilated Patients

Abstract

Introduction: Acute respiratory failure requiring mechanical ventilation is a leading cause of mortality in the intensive care unit. Although single peripheral blood oxygen saturation/fraction of inspired oxygen (SpO2/FiO2) ratios of hypoxemia have been evaluated to risk-stratify patients with acute respiratory distress syndrome, the utility of longitudinal SpO2/FiO2 ratios is unknown.

Objective: To assess time-based SpO2/FiO2 ratios ≤ 150-SpO2/FiO2 time at risk (SF-TAR)-for predicting mortality in mechanically ventilated patients.

Methods: Retrospective, observational cohort study of mechanically ventilated patients at 21 community and 2 academic hospitals. Association between the SF-TAR in the first 24 hours of ventilation and mortality was examined using multivariable logistic regression and compared with the worst recorded isolated partial pressure of arterial oxygen/fraction of inspired oxygen (P/F) ratio.

Results: In 28,758 derivation cohort admissions, every 10% increase in SF-TAR was associated with a 24% increase in adjusted odds of hospital mortality (adjusted odds ratio = 1.24; 95% confidence interval [CI] = 1.23-1.26); a similar association was observed in validation cohorts. Discrimination for mortality modestly improved with SF-TAR (area under the receiver operating characteristic curve [AUROC] = 0.81; 95% CI = 0.81-0.82) vs the worst P/F ratio (AUROC = 0.78; 95% CI = 0.78-0.79) and worst SpO2/FiO2 ratio (AUROC = 0.79; 95% CI = 0.79-0.80). The SF-TAR in the first 6 hours offered comparable discrimination for hospital mortality (AUROC = 0.80; 95% CI = 0.79-0.80) to the 24-hour SF-TAR.

Conclusion: The SF-TAR can identify ventilated patients at increased risk of death, offering modest improvements compared with single SpO2/FiO2 and P/F ratios. This longitudinal, noninvasive, and broadly generalizable tool may have particular utility for early phenotyping and risk stratification using electronic health record data in ventilated patients.

Conflict of interest statement

Disclosure Statement

Drs Adams, Rogers, and Liu received funding from the National Institutes of Health (NIH) National Heart, Lung, and Blood Institute related to the submitted work during the study (K12HL108964 [Adams], K23HL125663 [Rogers], NIH R35GM128672 [Liu]). The study was supported by the Permanente Medical Group Delivery Science research program. Dr Taylor received grant support from the NIH during the study (UL1 TR001860). The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIH. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Drs Schuler, Marelich, Fresco, Riedl, Baker, and Escobar have no conflicts of interest to disclose.

Figures

Figure 1

Histogram of duration of mechanical ventilation in hours in derivation cohort, truncated at 14 days (representing 92.6% of overall sample). The x-axis represents elapsed days. The y-axis represents frequency of patients with that duration of ventilation

Figure 2

Hospital mortality in all 3 patient cohorts across increasing levels of peripheral blood oxygen saturation/fraction of inspired oxygen (SpO2/FiO2) ratio time-at-risk categories on day 1 of ventilation. KPNC = Kaiser Permanente Northern California; MIMIC = Medical Information Mart for Intensive Care; UCD = University of California, Davis.