Unmasking hypoxemia: the role of standard PaO₂ in interpreting Arterial blood gas analysis

Background: In the assessment of acute respiratory failure (ARF), PaO2/FIO2 ratio is widely used, but may be misleading in the presence of hyperventilation-induced hypocapnia. The standard PaO2 (stPaO2), a theoretical value corrected for PaCO2, may improve clinical interpretation of gas exchange severity. Methods: We conducted an online survey among Italian physicians using a case vignette of three hypothetical patients with identical PaO2 values but differing PaCO2 levels. Participants were asked to rank the severity of the cases based solely on arterial blood gas analysis (ABG). A second round was offered after introducing the concept of stPaO2 and providing corresponding values. Results: A total of 2,241 (8.9%) physicians (median age 53 years, 54.1% male) completed the first round and 1,324 (59%) completed the second one of the survey. Initially, only 9.2% correctly identified the clinical severity  pattern-this increased significantly to 16.1% after introducing stPaO2 (p < 0.01). The improvement rate was higher among physicians with less than 10 years of clinical experience. Performance improved across all specialties, particularly in emergency and intensive care medicine. Conclusions: The introduction of stPaO2 significantly enhanced physicians' ability to interpret ABG results in ARF. Although its calculation assumes ideal physiological conditions, stPaO2 remains a useful tool for unmasking hypoxemia in hyperventilating patients. Including stPaO2 in ABG reports may support more accurate clinical decision-making, particularly in emergency and critical care settings.