A New ARDS Early Noninvasive Screening Protocol：Potential Value of SpO2 and FiO2 as a Diagnostic Tool

Abstract Background: A large number of recent studies have confirmed that the pulse oximetric saturation (SpO2)/fraction of inspired oxygen (FiO2) ratio (SFR) correlate well with PaO2/FiO2 ratio (PFR). However, whether SFR can replace PFR for the diagnosis and evaluate the severity of ARDS patients is unclearly. The purpose of this study is to explore potential value of SFR as a new diagnostic tool for ARDS, and establish a diagnostic process.Methods: 341 patients were included in this study, SFR and PFR values were recorded in the same time. 161 patients were used to establish the model, and 180 patients were used to verify the validity of the model. 161 groups of data were divide into hypoxic group (group H) and non-hypoxic group (group N) according to whether SpO2 was greater than 97%. For group H, the regression equation was established to describe the relationship between SFR and PFR. and calculated the value of SFR when PFR is 300. For group N, the correlation between each observation data and PFR were analyzed. Receiver operating characteristic (ROC) curve analysis was used to determine the diagnostic value of the index. Finally, a new diagnostic process was established for ARDS based on these results, and the reliability was verified with Berlin definition set as the gold standard for diagnosis and classification.Results: For group H the diagnostic linear equation is PFR = 0.9162*SFR-21.39 ( R2=0.66 , P<0.0001 ). After calculation, when PFR is 300, SFR is 352. For group N, There is a significant negative correlation between FiO2 and PFR((R= -0.521,P<0.0001)). The AUC of using FiO2 to diagnose ARDS was 0.694 (95%CI 0.571~0.817, P＜0.005). When the cutoff value of FiO2 was 39%, the sensitivity was 0.838 and the specificity was 0.545. Therefore, in this new diagnosis progress, when SpO2≤97%, if SFR≤352, ARDS may exist; when SpO2>97%, if FiO2min>39%, there may be ARDS. The sensitivity, specificity, NPV, PPV, and accuracy of the new diagnosis progress for ARDS were 91.1%, 76.7%, 89.6%, 79.6%, and 83.9%, respectively. Conclusions: There are potential value of SpO2 and FiO2 as a noninvasive diagnostic tool for ARDS.