The utility value of SpO2/FiO2 (S/F) and PaO2/FiO2 (P/F) ratios for predicting initiation and efficiency of HFNC in children with respiratory distress admitted in PICU

Background: The PaO₂/FiO₂ (P/F) ratio, defined as the partial pressure of oxygen (PaO₂) divided by the fraction of inspired oxygen (FiO₂), and the SpO₂/FiO₂ (S/F) ratio, defined as pulse oximetric saturation (SpO₂) divided by FiO₂, are key indicators of oxygenation status. This study aimed to evaluate the utility of S/F and P/F ratios in predicting the initiation and effectiveness of HFNC in children with respiratory distress. Methods: A prospective observational study of 133 children (1 month–14 years) with respiratory distress receiving HFNC was conducted. S/F and P/F ratios were measured at 0, 1, 12, and 24 hours after HFNC initiation. Outcomes assessed included ICU stay, hospital stay, and HFNC duration. Results: Among 133 children (35.34% females, 64.66% males; mean age 0.9 years, weight 7.8 kg), 62.42% had moderate respiratory distress per P/F ratio, while 76.69% had mild respiratory failure per S/F ratio. Both ratios improved significantly over time (p <0.05). A higher S/F ratio at initiation correlated with shorter ICU and hospital stays. The S/F ratio was a superior predictor of HFNC requirement (sensitivity: 85.29%, accuracy: 88.5%) compared to the P/F ratio (sensitivity: 41.91%, accuracy: 56.67%). ROC analysis confirmed strong predictive power for S/F (AUC 0.966). Conclusion: The S/F ratio is a reliable, non-invasive surrogate for the P/F ratio in identifying respiratory distress and HFNC need, reducing the necessity for arterial blood sampling.