Rationale and limitations of the SpO(2)/FiO(2) as a possible substitute for PaO(2)/FiO(2) in different preclinical and clinical scenarios

Although the PaO(2)/FiO(2) derived from arterial blood gas analysis remains the gold standard for the diagnosis of acute respiratory failure, the SpO2/FiO2 has been investigated as a potential substitute. The current narrative review presents the state of the preclinical and clinical literature on the SpO(2)/FiO(2) as a possible substitute for PaO(2)/FiO(2) and for use as a diagnostic and prognostic marker; provides an overview of pulse oximetry and its limitations, and assesses the utility of SpO(2)/FiO(2) as a surrogate for PaO(2)/FiO(2) in COVID-19 patients. Overall, 49 studies comparing SpO(2)/FiO(2) and PaO(2)/FiO(2) were found according to a minimal search strategy. Most were conducted on neonates, some were conducted on adults with acute respiratory distress syndrome, and a few were conducted in other clinical scenarios (including a very few on COVID-19 patients). There is some evidence that the SpO(2)/FiO(2) criteria can be a surrogate for PaO2/FiO2 in different clinical scenarios. This is reinforced by the fact that unnecessary invasive procedures should be avoided in patients with acute respiratory failure. It is undeniable that pulse oximeters are becoming increasingly widespread and can provide costless monitoring. Hence, replacing PaO(2)/FiO(2) with SpO(2)/FiO(2)may allow resourcelimited facilities to objectively diagnose acute respiratory failure.