Thursday September 6, 2007
S/F ratio (pulse Ox saturation / FiO2 ratio)

A very interesting study published recently in chest comparing S/F ratio (pulse Ox saturation / FiO2 ratio) with P/F ratio (PO2 / FiO2 ratio).

Study found that S/F ratios correlate with P/F ratios.

S/F ratio of 235 = P/F ratios of 200 and
S/F ratio of 315 = P/F ratio of 300

The correlation formula is

S/F = 64 + 0.84 x (P/F)

This is an important study from the clinical bedside pragmatic point of view as A-lines or ABGs may not be instantly available in many casses. Despite the ubiquity of SPO2 due to skin color, oximeter location, disease states like low cardiac output or methemoglobinemia, it may be a quick and instant indicator of underlying lung injury and need for more aggressive attention for early diagnosis and treatment in clinical practice.


Editors' comment: This is a very important read for all intensivists involve in everyday management of respiratory failures due to very simple but high diagnostic value in early recoginition and management of ALI / ARDS.





Reference: click to get abstract/article

1. Comparison of the SpO2/FIO2 Ratio and the PaO2/FIO2 Ratio in Patients With Acute Lung Injury or ARDS - Chest. 2007; 132:410-417