SpO₂/FiO₂ ratio (estimated P/F)
Noninvasive oxygenation index with estimated P/F equivalent.
Inputs
0 of 2%
%
When to use
- No arterial blood gas available.
Pearls and pitfalls
- Valid only when SpO₂ is 97% or lower (the oxygen dissociation curve flattens above that).
- S/F 235 ≈ P/F 200; S/F 315 ≈ P/F 300.
Why use
Allows ARDS screening without an arterial line.
S/F = SpO₂ ÷ FiO₂; estimated P/F = (S/F − 64) ÷ 0.84 (Rice)