SpO2/FiO2 Ratio on Hospital Admission Is an Indicator of Early Acute Respiratory Distress Syndrome Development Among Patients at Risk

Purpose: Oxygen saturation to fraction of inspired oxygen ratio (SpO2/FiO2) has been validated as a surrogate marker for partial pressure of oxygen to fraction of inspired oxygen ratio among mechanically ventilated patients with acute respiratory distress syndrome (ARDS). The validity of SpO2/FiO2 measurements in predicting ARDS has not been studied. Recently, a Lung Injury Prediction Score (LIPS) has been developed to help identify patients at risk of developing ARDS. Methods: This was a secondary analysis of the LIPS-1 cohort. A multivariate logistic regression included all established variables for LIPS, Acute Physiology and Chronic Health Evaluation 2, age, and comorbid conditions that could affect SpO2/FiO2. The primary outcome was development of ARDS in the hospital. The secondary outcomes included hospital mortality, hospital day of ARDS development, and hospital day of death. Results: Of the 5584 patients, we evaluated all 4646 with recorded SpO2/FiO2 values. Median SpO2/FiO2 in those who did and did not develop ARDS was 254 (100, 438) and 452 (329, 467), respectively. There was a significant association between SpO2/FiO2 and ARDS (P ≤ .001). The SpO2/FiO2 was found to be an independent predictor of ARDS in a “dose-dependent” manner; for SpO2/FiO2 < 100—odds ratios (OR) 2.49 (1.69-3.64, P < .001), for SpO2/FiO2 100 < 200—OR 1.75 (1.16-2.58, P = .007), and for SpO2/FiO2 200 < 300—OR 1.62 (1.06-2.42, P = .025). The discriminatory characteristics of the multivariable model and SpO2/FiO2 as a single variable demonstrated area under the curve (AUC) of 0.81 and AUC of 0.74, respectively. Conclusions: The SpO2/FiO2, measured within the first 6 hours after hospital admission, is an independent indicator of ARDS development among patients at risk.