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.

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.

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.

The SpO₂/FiO₂, measured within the first 6 hours after hospital admission, is an independent indicator of ARDS development among patients at risk.