Non-invasive SpO2/FiO2 ratio (SFR) as surrogate for PaO2/FiO2 ratio (PFR): A scoping review

Patient oxygenation significantly impacts clinical outcomes, and continuous monitoring is essential, especially in critical care settings where hypoxia is the leading cause of mortality. PFR (PaO2/FiO2 ratio or P/F ratio) is an invasive method for measuring oxygenation requiring arterial blood gas (ABG) sampling, however it carries complications making non-invasive methods more desirable. SFR (SpO2/FiO2 ratio or S/F ratio), a non-invasive tool based on pulse oximetry, provides a cost-effective and rapid way to monitor oxygenation status, especially in settings where advanced methods are unavailable. A total of 575 articles were screened from databases including Web of Science, Scopus, PubMed, and CINAHL, with 32 articles meeting the inclusion criteria for this scoping review wherein SFR was used as a surrogate for PFR and a diagnostic tool for acute lung injury and ARDS. A total of 81,637 patient records were analyzed, including ABG values, pulse oximetry readings, mechanical ventilator settings, and patient diagnoses. The study population included adults, pediatric patients, and neonates admitted to critical care units, with common diagnoses including acute hypoxemic respiratory failure, ARDS, and COVID-19. In the context of COVID-19, SFR was used to predict the need for mechanical ventilation, with a cut-off of 300 indicating a threshold for imminent ventilation requirement. The studies demonstrated statistically significant sensitivity and specificity for SFR, highlighting its utility as a non-invasive tool for assessing oxygenation status. SFR has shown potential as a reliable non-invasive surrogate for determining oxygenation status across all populations.