Calculate the PaO₂/FiO₂ ratio in mmHg or kPa with Berlin ARDS severity (mild, moderate, severe) and the SpO₂/FiO₂ ratio when no blood gas is available.
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About this tool
PaO₂/FiO₂ ratio with Berlin ARDS severity and SpO₂/FiO₂.
How to use P/F Ratio Calculator
Enter PaO₂ in mmHg or kPa and the FiO₂.
Tick whether the patient is on PEEP or CPAP of at least 5 cmH₂O.
Read the P/F ratio and ARDS category.
Worked example
A PaO₂ of 85 mmHg on 50% oxygen gives a P/F ratio of 170, in the moderate ARDS range.
What is a normal P/F ratio?
About 400–500 mmHg in healthy lungs. Below 300 indicates impaired oxygenation.
Does a low P/F ratio mean ARDS?
Not on its own. ARDS also needs acute onset, bilateral opacities and no full explanation by heart failure.
References
Explore Medical & Clinical Tools · More practical guides
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