Oxygenation saturation index in neonatal hypoxemic respiratory failure

This study aimed to assess the validity of the oxygenation saturation index (OSI) and the ratio of oxygen saturation to the fraction of inspired oxygen (F_IO₂) (S/F ratio) with percutaneous oxygen saturation (OSI_SpO2 and the S_p/F ratio) and to evaluate the correlation between these values and the oxygen index (OI). It also determined their cut-off values for predicting OI in accordance with neonatal hypoxic respiratory failure severity.

We reviewed the data of 77 neonates (gestational age 31.7 ± 6.1 weeks; birthweight, 1768 ± 983 g) requiring invasive mechanical ventilation between 2013 and 2020, 1233 arterial blood gas samples in total. We calculated the OI, OSI_SpO2, OSI with arterial oxygen saturation (SaO₂) (OSI_SaO2), S_p/F ratio, and the ratio of SaO₂ to F_IO₂ (S_a/F ratio).

The regression and Bland-Altman analysis showed good agreement between OSI_SpO2 or the S_p/F ratio and OSI_SaO2 or the S_a/F ratio. Although a significant positive correlation was found between OSI_SpO2 and OI, OSI_SpO2 was overestimated in SpO₂ > 98% with a higher slope of the fitted regression line than that below 98% of SpO₂. Furthermore, receiver-operating characteristic curve analysis using only SpO₂ ≤ 98% samples showed that the optimal cut-off points of OSI_SpO2 and the S_p/F ratio for predicting OI were: OI 5, 3.0 and 332; OI 10, 5.3 and 231; OI 15, 7.7 and 108; OI 20, 11.0 and 149; and OI 25, 17.1 and 103, respectively.

The cut-off OSI_SpO2 and S_p/F ratio values could allow continuous monitoring for oxygenation changes in neonates with the potential for wider clinical applications.