A Continuous and Noninvasive Method to Estimate Pao2/Fio2 Ratio.

Objectives: To validate a method for continuously estimating the Pao₂/Fio₂ (PF) ratio in all critically ill pediatric patients using only standard continuous data monitoring.

Design: Retrospective study on a high temporal resolution database.

Setting: PICU in Montreal, QC, Canada.

Patients/subjects: We included any patients admitted from May 2015 to May 2023 who had an arterial blood gas (ABG) with concurrent continuous pulsed oximetry saturation (Spo₂) values. We used our previously validated mathematical model to determine the magnitude of hypoxemia by computing the estimated ePao₂/Fio₂ (ePF) ratio and comparing it to the Spo₂/Fio₂ (SF), using PF ratio as the reference standard.

Interventions: None.

Measurements and main results: We analyzed a total of 20,828 ABGs. When Spo₂ was below or equal to 97%, the ePF ratio showed a significantly better hypoxemia classification (none, light/moderate, or severe) than the SF ratio (0.80 vs. 0.72; p < 0.001), a lower fixed bias (16.26 vs. -35.24; p < 0.001), a lower mean absolute error (37.92 vs. 63.93; p < 0.001) and a lower proportional bias (slope of 1.01 vs. 0.81; p < 0.001). ePF ratio has also a better limits of agreement difference from Bland-Altman plot (248.10 vs. 292.45; p < 0.001) and coefficient of determination (0.68 vs. 0.59; p < 0.001). When Spo₂ was above 97%, the ePF ratio had better classification with Kappa (0.53 vs. 0.43; p < 0.001) and lower fixed bias (-0.63 vs. 65.68; p < 0.001).

Conclusions: The PF ratio based on ePF allows for a continuous estimation of hypoxemia severity with a better performance than the SF ratio.