How do I calculate P/F ratio from SpO2?

When ABG is unavailable, SpO2-based P/F (SF ratio) can be estimated. SpO2 97% is approximately PaO2 97 mmHg on room air. SF ratio < 315 correlates with P/F < 300.

Does FiO2 affect P/F ratio interpretation?

Yes - P/F ratio should be measured at consistent FiO2. The ARDSNet protocol recommends standardising at FiO2 0.4-0.5 with appropriate PEEP ladder settings before classifying severity.

P/F Ratio (PaO2/FiO2) - Oxygenation Index

Calculate P/F ratio (PaO2 / FiO2) to assess oxygenation impairment. Normal > 400-500 mmHg; P/F > 300 = no ARDS; 200-300 = mild ARDS; 100-200 = moderate ARDS; < 100 = severe ARDS. Monitor trends to guide ventilator management.

⚕ Clinical Disclaimer: These calculators are for educational and reference purposes only. Always verify results with qualified clinical judgment and current clinical guidelines. Do not use as a sole basis for medical decisions.

How to Use

Enter the values for the scenario you are assessing. Calculate P/F ratio (PaO2 / FiO2) to assess oxygenation impairment. Normal > 400-500 mmHg; P/F > 300 = no ARDS; 200-300 = mild ARDS; 100-200 = moderate ARDS; < 100 = severe ARDS. Monitor trends to guide ventilator management. Use the p/f ratio result to inform your calculation.

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