respiratory critical-care

SpO₂/FiO₂ (S/F) Ratio

Non-invasive surrogate for the PaO₂/FiO₂ ratio using pulse oximetry. Avoids arterial blood gas requirement. S/F ratio <315 correlates with ARDS (P/F <300).

Score interpretation

Severe ARDS Equivalent 0–148

S/F <149 — equivalent to P/F <100 (severe ARDS)

→ Lung-protective ventilation; neuromuscular blockade; prone positioning ≥16h/day; ECMO consideration

Moderate ARDS Equivalent 149–234

S/F 149–234 — equivalent to P/F 100–199 (moderate ARDS)

→ Lung-protective ventilation; high PEEP strategy; prone positioning if refractory; referral to specialist centre

Mild ARDS Equivalent 235–314

S/F 235–314 — equivalent to P/F 200–300 (mild ARDS / ALI)

→ Lung-protective ventilation (TV 6 mL/kg IBW); PEEP ≥5 cmH₂O; treat underlying cause

Normal / Non-ARDS ≥ 315

S/F ≥315 — P/F >300, not consistent with ARDS

→ Reassess oxygen delivery; consider other diagnoses if hypoxic

Interpretation bands for the S/F Ratio. Apply clinical judgement and local guidance.

References

Rice TW et al. Comparison of the SpO2/FIO2 ratio and the PaO2/FIO2 ratio in patients with acute lung injury. Chest. 2007;132(2):410–417.

Curated clinical cross-links plus same-class fallbacks.

Calculators

Drugs

Pathways

Decision support only — verify against a current formulary, NICE, or your local guideline before clinical use.

Score interpretation

References

Related