SF Ratio as an Alternative Marker for PF Ratio in Paediatric Index of Mortality 3 Score at a Tertiary Care Centre

Abstract

Introduction: Pediatric Index of Mortality 3 (PIM 3) score is a mortality prediction score used in paediatric intensive care units. The PF (PaO2 / FiO2) ratio is a component of the PIM 3 score. To obtain the ratio an arterial blood gas would be required. The SF (SpO2 / FiO2) ratio provides a less invasive method of monitoring. With this study, we aimed to see if SF ratio can replace the PF ratio component of the PIM 3 score.

Methods: It was a prospective study, where 101 critically ill children were included over a period of 18 months. Data was analyzed by mean, standard deviation (SD), frequency and percentages. Intra class comparison as well as ROC curve analysis was used to test the reliability of SF ratio. PIM 3 scores were obtained using PIM 3 calculators available on standard reference websites. Derived PIM 3 scores were obtained using SF ratio instead of the PF ratio. The two scores were compared.

Results: The mean age in the study was 4.5 years. The mean PF ratio was 281.7 ± 216.7 and mean SF ratio was 297.7 ± 115.8. Maximum mortality was seen in children with PIM 3 score between 10 and 30. The intraclass correlation coefficient was 0.997, interpreted as excellent agreement. The area under the ROC curve for mortality prediction using PIM 3 score was 0.814 and using PIM 3 with SF ratio was 0.819.

Conclusions: SF ratio can be used as a reliable, non-invasive, alternative marker for PF ratio in the paediatric index of mortality score.