A prospective observational study to compare the ratio of Pulse oximetric saturation (Spo2)/Fraction of inspired oxygen (Fio2) {S/F ratio} with the ratio of Partial pressure of oxygen(Pao2)/ Fio2 {P/F ratio} among the critically ill children requiring respiratory support in a pediatric intensive care unit

Abstract

Objectives: To compare and analyse the relationship between Pao2/Fio2 (P/F) ratio and Spo2 /Fio2 (S/F) ratio in critically ill children requiring respiratory support. Materials and Methods: Our study was done over a period of 7 months (February 2016-August 2016) in the Paediatric Intensive care Unit (PICU), in a Tertiary care Hospital. All Children admitted in PICU, who require respiratory support (Noninvasive/Invasive) are recruited in the study. Children with congenital heart disease, chronic lung disease, abnormal haemoglobin, etc., are excluded from the study. Children for whom the definitive Fio2 delivery is not known (eg: face mask, Head box etc.) are also excluded. S/F ratio and P/F ratio was calculated twice for each participant, once at the time of recruitment and again at the time of deterioration (requiring escalation in the respiratory support) or 24 hours after recruitment, whichever is the earliest. Results: We obtained a total of 250 samples from 125 participants. Among 125 children, 112 (89.5%) required invasive ventilation, 5 (4%) required face mask Non-invasive ventilation, 1 (0.8%) required nasopharyngeal CPAP and 7 (5.7%) required high flow nasal cannula therapy. In our study, 27 (21.6%) had ARDS. Our study showed, S/F ratio of less than 180 corresponds well with P/F ratio <200, with sensitivity and specificity of 90% and 59% respectively (AUROC-0.8). In other words, any child who require Fio2 of 50% or more to maintain a saturation of 90% (S/F ratio<180) are likely to have ARDS (P/F <200). Conclusion: Our study showed a strong correlation between S/F ratio and P/F ratio. S/F ratio (<180) helps in early identification of children at risk of ARDS, especially in Paediatric Emergency and in secondary level settings where arterial blood gas are not available.