SOFA Score Calculation

The Sequential Organ Failure Assessment (SOFA) score quantifies organ dysfunction across 6 systems. Each component scores 0-4, with a total range of 0-24. Higher scores indicate greater organ dysfunction.

When to Use This Skill

• User asks about SOFA score calculation
• Sepsis-3 criteria assessment (SOFA >= 2 indicates organ dysfunction)
• Mortality prediction or severity stratification
• Comparing organ dysfunction between cohorts
• Calculating delta-SOFA (change from baseline)

Components and Scoring

Note: Vasopressor doses are in mcg/kg/min. UO is urine output in mL/day.

Pre-computed Table

MIMIC-IV provides a pre-computed SOFA table with hourly values:

SELECT
    stay_id,
    hr,
    starttime,
    endtime,
    respiration_24hours,
    coagulation_24hours,
    liver_24hours,
    cardiovascular_24hours,
    cns_24hours,
    renal_24hours,
    sofa_24hours
FROM mimiciv_derived.sofa
WHERE hr = 24;  -- 24 hours after ICU admission

Required Tables for Custom Calculation

• mimiciv_icu.icustays - ICU stay identifiers
• mimiciv_derived.bg - Blood gas for PaO2/FiO2 (specimen = 'ART.')
• mimiciv_derived.chemistry - Creatinine
• mimiciv_derived.enzyme - Bilirubin
• mimiciv_derived.complete_blood_count - Platelets
• mimiciv_derived.gcs - Glasgow Coma Scale
• mimiciv_derived.urine_output_rate - Daily urine output
• mimiciv_derived.ventilation - Ventilation status
• mimiciv_derived.norepinephrine, epinephrine, dopamine, dobutamine - Vasopressors

Critical Implementation Notes

1. Time Window: The score uses the worst value in a 24-hour rolling window. SOFA calculated at hour 24 uses data from hours 0-24.

2. Respiratory Score: Requires interaction between PaO2/FiO2 ratio AND ventilation status:

   • Scores of 3 or 4 require mechanical ventilation
   • The lowest PaO2/FiO2 is tracked separately for ventilated vs non-ventilated periods

3. FiO2 Sources: FiO2 can come from blood gas measurement OR charted FiO2. When not documented, estimate from supplemental O2 device.

4. Vasopressor Units: All vasopressor doses must be in mcg/kg/min. Weight is often estimated (check mimiciv_derived.weight_durations).

5. GCS in Sedated Patients: For sedated/intubated patients, use pre-sedation GCS or assume normal (GCS=15). The verbal component may be 0 for intubated patients - this is handled specially.

6. Arterial Blood Gas: Use only arterial specimens (specimen = 'ART.') for PaO2/FiO2.

7. Missing Components: Missing data is imputed as 0 (normal) in the final score. Document which components are missing; do not claim complete scores when data is absent.

8. Urine Output Calculation: Uses uo_tm_24hr to verify 24 hours of data available before calculating rate.

Example: Get SOFA at 24h for All ICU Stays

SELECT
    ie.stay_id,
    ie.subject_id,
    ie.hadm_id,
    s.sofa_24hours,
    s.respiration_24hours,
    s.coagulation_24hours,
    s.liver_24hours,
    s.cardiovascular_24hours,
    s.cns_24hours,
    s.renal_24hours
FROM mimiciv_icu.icustays ie
LEFT JOIN mimiciv_derived.sofa s
    ON ie.stay_id = s.stay_id
    AND s.hr = 24
ORDER BY s.sofa_24hours DESC NULLS LAST;

Example: Delta-SOFA (Change Over Time)

WITH sofa_change AS (
    SELECT
        stay_id,
        sofa_24hours AS sofa_day1,
        LEAD(sofa_24hours, 24) OVER (
            PARTITION BY stay_id ORDER BY hr
        ) AS sofa_day2
    FROM mimiciv_derived.sofa
    WHERE hr = 24 OR hr = 48
)
SELECT
    stay_id,
    sofa_day1,
    sofa_day2,
    sofa_day2 - sofa_day1 AS delta_sofa
FROM sofa_change
WHERE sofa_day2 IS NOT NULL;

References

• Vincent JL et al. "The SOFA (Sepsis-related Organ Failure Assessment) score to describe organ dysfunction/failure." Intensive Care Medicine. 1996;24(7):707-710.
• Singer M et al. "The Third International Consensus Definitions for Sepsis and Septic Shock (Sepsis-3)." JAMA. 2016;315(8):801-810.