To compare PaO2/FiO2 (PF ratio) to SpO2/FiO2 (SF ratio) and oxygenation index (OI) to oxygenation saturation index (OSI) for predicting short term outcomes [mortality, progression to ventilation and ventilator free days (VFD)] and compare trends of S/F and OSI in predicting early mortality in children with acute hypoxemic respiratory distress.

This prospective observational study included 200 consecutive children with acute hypoxemic respiratory distress. Serial PF and SF ratios calculated at 0, 6, 24 and 48 h were compared and their trends were utilized for prediction of 28 d mortality. Same was done in ventilated patients using OI and OSI.

SF ratio at admission had a 72% sensitivity and 60% specificity while PF had a sensitivity of 78% and a specificity of 75% for prediction of mortality. The area under the curve (AUC) for SF ratio was 0.82 (CI: 0.688–0.915). Serial SF ratios accurately predicted mortality. OI had sensitivity of 92% and specificity of 95% in predicting 24 and 48 h mortality. OSI had 95% sensitivity and 92% specificity in predicting mortality with AUC 1.000 (CI- 1.00–1.00) at 24 and 48 h post ventilation. Serially increasing OI and OSI trends had an inverse correlation with VFDs (p <0.01).

SF is a reliable surrogate for PF and a useful predictor of progression to ventilation and survival at discharge while OSI is a useful marker of worsening hypoxia and mortality in ventilated patients.