Diagnostic Performance of the Pulse Oxygen Saturation to Fraction of Inspired Oxygen Ratio in Adults with Acute Hypoxemic Respiratory Failure in an Intensive Care Unit in Sub-Saharan Africa
Introduction: The SpO2/FiO2 ratio (S/F) is a non-invasive tool for diagnosing acute hypoxemic respiratory failure, particularly valuable in resource-limited settings where arterial blood gas analysis is scarce. This study aims to determine S/F ratio cut-offs corresponding to PaO2/FiO2 (P/F) ratios used in AHRF patients in a Sub-Saharan African population, with a focus on defining thresholds for spontaneously ventilating patients. Methods: We conducted a retrospective cohort study in the intensive care unit at Douala General Hospital. Medical records of patients over 18 years of age, hospitalised between January 1, 2021 and July 30, 2022 and having benefited from at least one arterial blood gas measurement were reviewed. Documented arterial blood gas measurements were considered if the records had a traceable matched SpO2 and FiO2 recorded within 30 minutes of the measurement. Files with any documented cause of chronic respiratory failure were excluded. Data were analyzed using R version 4.5.1. Linear regression models were employed. The level of statistical significance was set at P < 0.05. Results: A very strong correlation was found between the S/F and P/F ratios (r > 0.8). The equation of the straight line that characterised the linear relationship between S/F ratio and P/F ratio was ln(S/F) = 1.196 + 0.805 ln(P/F) for spontaneously ventilating patients and ln(S/F) = 1.810 + 0.659 ln(P/F) for mechanically ventilated patients, with R2 values of 0.80 and 0.76, respectively. The S/F ratio cut-offs corresponding to P/F ratios of 300 mmHg, 200 mmHg, and 100 mmHg were approximately 325, 235, and 135 for spontaneously ventilating patients and 260, 200, and 125 for mechanically ventilated patients with PEEP > 5 cmH2O. Conclusion: This study demonstrates a strong correlation between the S/F and P/F ratios in Sub-Saharan Africa. The findings highlight the clinical utility of the S/F ratio as a practical, non-invasive tool for diagnosing acute hypoxemic respiratory failure, particularly in resource-limited settings. Tailoring cut-offs according to ventilation status may optimise patient triage and treatment decisions, contributing to better outcomes.
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