F Ratio)
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sf_ratio

R Documentation

SpO2/FiO2 Ratio (S/F Ratio)

Description

Calculates the SpO2/FiO2 (S/F) ratio, a non-invasive surrogate for the PaO2/FiO2 (P/F) ratio used to assess the severity of hypoxemia and acute respiratory distress syndrome (ARDS)

[Image of oxygen gradient diagram] . The S/F ratio correlates with the P/F ratio, with S/F values of 235 and 315 corresponding approximately to P/F values of 200 and 300, respectively.

Usage

sf_ratio(spo2_percent, fio2_percent)

Arguments

`spo2_percent`	Numeric. Oxygen saturation as measured by pulse oximetry (0-100%).
`fio2_percent`	Numeric. Fraction of Inspired Oxygen (can be entered as a percentage e.g., 40, or decimal e.g., 0.40).

Value

A list containing:

`SF_Ratio`	The calculated S/F ratio.
`Interpretation`	Clinical interpretation regarding ARDS severity.
`Estimated_PF_Ratio`	Approximate corresponding P/F ratio range.

References

Rice TW, Wheeler AP, Bernard GR, et al. Comparison of the SpO2/FIO2 ratio and the PaO2/FIO2 ratio in patients with acute lung injury or ARDS. Chest. 2007;132(2):410-417. doi:10.1378/chest.07-0617

Examples


# Example 1: Severe Hypoxemia (ARDS)
# SpO2 88%, FiO2 0.60
# Ratio = 88 / 0.6 = 146.7
sf_ratio(88, 60)

# Example 2: Normal/Mild
# SpO2 98%, Room Air (0.21)
# Ratio = 98 / 0.21 = 466.7
sf_ratio(98, 21)

cliot documentation built on Dec. 1, 2025, 1:06 a.m.