Peripheral Oxygen Saturation Targets and Hyperoxemia in Critical Care: Influence of pH, FiO2, and Respiratory Failure

Oxygen therapy is a cornerstone in the treatment of critically ill patients. However, excess oxygen administration may promote oxidative cellular injury once hemoglobin is fully saturated and additional oxygen remains dissolved, enhancing reactive oxygen species formation. The combined impact of oxygen administration, pH, and respiratory failure on hyperoxemia across saturation ranges is not well understood. We conducted a retrospective study at a tertiary center to assess how these factors modify hyperoxemia frequency in adult ICU patients. Continuous SpO2 measurements were aligned with arterial blood gases (PaO2, pH, FiO2), and hyperoxemia was evaluated using predefined PaO2 thresholds (>120 mmHg and >150 mmHg). Among 21,406 patients with 717,064 paired measurements, prolonged hyperoxemia occurred in over half of mechanically ventilated patients, most commonly in those without or with mild-to-moderate respiratory failure. Acidotic states were associated with higher PaO2 values at comparable SpO2 levels, consistent with a rightward shift in the oxygen-hemoglobin dissociation curve. SpO2 values ≥ 98% were consistently associated with hyperoxemia, whereas 96-97% generally corresponded to PaO2 within physiological ranges. Higher FiO2 markedly increased hyperoxemia probability, allowing derivation of pH-stratified FiO2 exposure limits. Our findings highlight the importance of individualized oxygen therapy, considering pH and respiratory failure phenotype to guide safer oxygen management.