Each subscore uses the worst value in the window, not one snapshot in time. SOFA is scored over a defined assessment period — conventionally 24 hours. Within that window, each of the six organ systems is scored from its own worst (most abnormal) recorded value, and those six subscores are summed for the 0–24 total. The six inputs don't need to come from the same exact moment — each represents the worst derangement for that system during the interval.
Common windows in practice:
A component not measured in the window is conventionally scored as normal (0), not left blank. For the cardiovascular component, a vasopressor dose is generally expected to have run for a sustained period (commonly ≥1 hour) before it counts toward the score.
SOFA is most useful as a trend — serial scores across windows — rather than a single value. A rise of ≥2 points from baseline is part of the Sepsis-3 definition of sepsis-associated organ dysfunction.
Imputes PaO₂ from SpO₂ (Ellis solution to the Severinghaus equation), estimates FiO₂ from the delivery device, then computes PaO₂:FiO₂.
1. SpO₂ → PaO₂ — Ellis's closed-form inversion of the Severinghaus oxyhemoglobin dissociation equation (Ellis RK, J Appl Physiol 1989;67(2):902), the same method used by Open Critical Care's Imputed PaO₂ from SpO₂ Calculator. Given S = SpO₂ as a fraction:
SpO₂ readings of 100% are treated as 99.6% before imputation, since the equation is undefined at S = 1.
2. Device + flow → FiO₂ — standard clinical low-flow approximation (≈4% FiO₂ per L/min above room air for nasal cannula), consistent with the estimation tables referenced in MDCalc's SOFA score evidence section:
3. P:F ratio → SOFA respiratory points — thresholds per the original SOFA respiratory criterion (MDCalc, SOFA score):
4. What counts as respiratory support — the classic SOFA respiratory criterion (Vincent et al., Intensive Care Med 1996, and MDCalc's definition) counts only invasive mechanical ventilation or CPAP. The status of high-flow nasal cannula is genuinely unsettled: institutions and protocols differ, and some pandemic-era triage tools treat HFNC as equivalent support. Rather than deciding for you, this calculator offers both HFNC variants explicitly so the selection matches your local protocol. Every other device's support status is inferred from the selection itself and shown read-only, with a manual override available for edge cases the device list doesn't capture (for example noninvasive ventilation delivered by a mask selected here only for its FiO₂ estimate).
Use the most abnormal value over the assessment period (typically 24 h).
| System | Basis | Pts |
|---|---|---|
| Respiratory | PaO₂:FiO₂ – | 0 |
| Coagulation | Platelets – | 0 |
| Liver | Bilirubin – | 0 |
| Cardiovascular | No hypotension | 0 |
| CNS | GCS – | 0 |
| Renal | Creatinine – | 0 |
| PaO₂:FiO₂ | Pts | |
|---|---|---|
| ≥ 400 mmHg | — | 0 |
| < 400 mmHg | — | 1 |
| < 300 mmHg | — | 2 |
| < 200 mmHg | + ventilatory support | 3 |
| < 100 mmHg | + ventilatory support | 4 |