Comparison of the Pulse Oximetric Saturation/Fraction of Inspired Oxygen Ratio and the Pao2/Fraction of Inspired Oxygen Ratio in Children

BackgroundAlthough diagnostic criteria for acute lung injury (ALI) and ARDS are clear, invasive arterial sampling is required for computation of Pao2/fraction of inspired oxygen (Fio2) [PF] ratios. The pulse oximetric saturation (Spo2)/Fio2 (SF) ratio may be a reliable noninvasive alternative to the PF ratio for identifying children with lung injury.MethodsWe electronically queried blood gas measurements from two tertiary care pediatric ICUs (PICUs). Included in the analysis were corresponding measurements of Spo2, Pao2, and Fio2 charted within 15 min of each other when Spo2 values were between 80% and 97%. Computed PF and SF ratios were compared to identify threshold values for SF ratios that correspond to PF criteria for ALI (≤ 300) and ARDS (≤ 200). Data from one PICU were used for derivation and validated with measurements from the second PICU.ResultsFrom the 1,298 observations in the derivation data set, SF ratio could be predicted by the regression equation SF = 76 + 0.62 × PF (p < 0.0001, R2 = 0.61). SF ratios of 263 and 201 corresponded to PF ratios of 300 and 200, respectively. The ALI SF cutoff of 263 had 93% sensitivity and 43% specificity, and the ARDS cutoff of 201 had 84% sensitivity and 78% specificity. Applying these values to the 1,845 observations in the validation data set yielded a sensitivity of 86% and specificity of 47% for ALI and a sensitivity of 68% and specificity of 84% for ARDS.ConclusionSF ratio is a reliable noninvasive marker for PF ratio to identify children with ALI or ARDS.