Dynamics of Oxygen Reserve Index and Arterial Oxygen Partial Pressure in Children: A Prospective Observational Study

Aims The Oxygen Reserve Index (ORI) is a novel, noninvasive parameter that reflects moderate hyperoxic states. However, its relationship with PaO 2 in the pediatric population remains poorly understood. We investigated the ORI‐PaO 2 relationship during pediatric cardiac surgery and identified its influencing factors. Methods This prospective observational study included 98 pediatric patients (< 7 years of age) who underwent cardiac surgery for congenital heart defects. ORI and PaO 2 were measured at FiO 2 levels of 0.21, 0.5, and 0.8, both before and after cardiopulmonary bypass (CPB). Linear mixed models and regression analyses were used to examine the relationship between ORI and PaO 2 by incorporating covariates such as hemoglobin (Hb), ejection fraction (EF), and perfusion index (PI). Locally weighted regression analysis was conducted to identify potential PaO 2 thresholds influencing this relationship. Results A total of 487 data samples were analyzed. A nonlinear relationship between ORI and PaO 2 was observed, with a threshold of 245 mmHg dividing the data into two distinct ranges. Pearson correlation coefficients between ORI and PaO 2 were significant in both ranges: 0.516 (PaO 2 ≤ 245 mmHg, p < 0.001) and 0.151 (PaO 2 > 245 mmHg, p = 0.035). Although Hb level and EF showed no impact, only PI had a mildly negative relationship with ORI before CPB. The relationship between ORI and PaO 2 remained consistent across both pre‐ and post‐CPB periods ( r 2 = 0.304 and 0.337, respectively). Conclusion ORI consistently correlates with PaO 2 in children undergoing cardiac surgery, is unaffected by Hb or EF, and may serve as a useful tool for monitoring oxygenation trends. Trial Registration ClinicalTrials.gov: NCT03130023