Limitations of SpO2/FiO2 for ARDS classification

Summary

Across three ICU databases totaling 708 ARDS patients, SpO2/FiO2 frequently misclassified ARDS severity compared with reference measures, indicating systematic limitations of pulse oximetry-based oxygenation indices. Findings support cautious use of SpO2/FiO2 for severity stratification and trial enrollment.

Key Findings

• In 708 ARDS patients from three high-resolution ICU databases, SpO2/FiO2 frequently misclassified ARDS severity compared with reference standards.
• Time-matched SpO2 data showed systematic limitations that can bias severity stratification.
• Findings question the use of SpO2/FiO2 as a surrogate for PaO2/FiO2 in ARDS classification.

Clinical Implications

Where feasible, prioritize PaO2/FiO2 from arterial blood gas for ARDS severity classification and use SpO2/FiO2 with caution, accounting for oximetry bias and patient-specific factors (skin pigmentation, perfusion, vasopressors). Re-evaluate trial eligibility criteria and ventilatory targets that rely solely on SpO2.

Limitations

• Retrospective observational design limits causal inference
• Potential database coding/measurement variability and unmeasured confounders

Future Directions

Prospective studies comparing SpO2/FiO2 and PaO2/FiO2 under standardized calibration and diverse patient phenotypes; development of corrected SpO2-based indices integrating perfusion and sensor bias.