Comparison of the SpO2/FIO2 Ratio and the PaO2/FIO2 Ratio in Patients With Acute Lung Injury or ARDS

摘要

Background: The diagnostic criteria for acute lung injury (ALI) and ARDS utilize the PaO2fraction of inspired oxygen (FIO2) [P/F] ratio measured by arterial blood gas analysis to assess thendegree of hypoxemia. We hypothesized that the pulse oximetric saturation (SpO2)/FIO2 (S/F) rationcan be substituted for the P/F ratio in assessing the oxygenation criterion of ALI.nMethods: Corresponding measurements of SpO2 (values < 97%) and PaO2 from patients enrollednin the ARDS Network trial of a lower tidal volume ventilator strategy (n u0001 672) were comparednto determine the relationship between S/F and P/F. S/F threshold values correlating with P/Fnratios of 200 (ARDS) and 300 (ALI) were determined. Similar measurements from patientsnenrolled in the ARDS Network trial of lower vs higher positive end-expiratory pressure (n u0001 402)nwere utilized for validation.nResults: In the derivation data set (2,613 measurements), the relationship between S/F and P/Fnwas described by the following equation: S/F u0001 64 u0002 0.84 u0003 (P/F) [p < 0.0001; r u0001 0.89). An S/Fnratio of 235 corresponded with a P/F ratio of 200, while an S/F ratio of 315 corresponded with anP/F ratio of 300. The validation database (2,031 measurements) produced a similar linearnrelationship. The S/F ratio threshold values of 235 and 315 resulted in 85% sensitivity with 85%nspecificity and 91% sensitivity with 56% specificity, respectively, for P/F ratios of 200 and 300.nConclusion: S/F ratios correlate with P/F ratios. S/F ratios of 235 and 315 correlate with P/F ratiosnof 200 and 300, respectively, for diagnosing and following up patients with ALI and ARDS.