Sirs Criteria

SIRS Criteria Calculation

The Systemic Inflammatory Response Syndrome (SIRS) criteria quantify the inflammatory response. Historically used for sepsis definition (SIRS >= 2 + suspected infection), now largely replaced by Sepsis-3 but still relevant for research and comparison.

When to Use This Skill

• Historical sepsis research (pre-Sepsis-3 definitions)
• Inflammatory response quantification
• Comparing SIRS vs Sepsis-3 criteria
• Identifying patients with systemic inflammation
• Quality metrics using legacy definitions

SIRS Criteria (0-4 Points)

Each criterion met = 1 point:

SIRS Positive: >= 2 criteria met

Pre-computed Table

SELECT
    subject_id,
    hadm_id,
    stay_id,
    sirs,
    temp_score,
    heart_rate_score,
    resp_score,
    wbc_score
FROM mimiciv_derived.sirs;

Component Details

Temperature

• Uses min and max from first 24 hours
• Score = 1 if temp_min < 36C OR temp_max > 38C

Heart Rate

• Uses max from first 24 hours
• Score = 1 if heart_rate_max > 90

Respiratory

• Uses RR max OR PaCO2 min (arterial)
• Score = 1 if resp_rate_max > 20 OR paco2_min < 32

White Blood Cell Count

• Uses min, max, and bands from first 24 hours
• Score = 1 if wbc_min < 4 OR wbc_max > 12 OR bands_max > 10%

Critical Implementation Notes

1. Band Forms: The presence of > 10% immature neutrophils (bands) counts as the WBC criterion, even if total WBC is normal.

2. Arterial Blood Gas: PaCO2 uses only arterial specimens from first_day_bg_art table.

3. Missing Data: Missing components imputed as 0 (normal). This may underestimate true SIRS.

4. First Day Only: Calculated using first 24 hours of ICU stay data.

5. SIRS vs Sepsis-3:

   • SIRS >= 2 + suspected infection = old sepsis definition
   • Sepsis-3 uses SOFA >= 2 + suspected infection
   • SIRS is more sensitive but less specific for mortality

Example: SIRS Distribution

SELECT
    sirs,
    COUNT(*) AS n_patients,
    ROUND(100.0 * COUNT(*) / SUM(COUNT(*)) OVER(), 1) AS pct
FROM mimiciv_derived.sirs
GROUP BY sirs
ORDER BY sirs;

Example: Compare SIRS vs Sepsis-3 Sensitivity

WITH classifications AS (
    SELECT
        si.stay_id,
        si.sirs >= 2 AS sirs_positive,
        s3.sepsis3
    FROM mimiciv_derived.sirs si
    LEFT JOIN mimiciv_derived.sepsis3 s3
        ON si.stay_id = s3.stay_id
    WHERE s3.stay_id IS NOT NULL  -- has suspected infection
)
SELECT
    sirs_positive,
    sepsis3,
    COUNT(*) AS n
FROM classifications
GROUP BY sirs_positive, sepsis3
ORDER BY 1, 2;

Example: SIRS Components in Septic Patients

SELECT
    'Temperature' AS component,
    ROUND(AVG(temp_score), 2) AS prevalence
FROM mimiciv_derived.sirs si
INNER JOIN mimiciv_derived.sepsis3 s3 ON si.stay_id = s3.stay_id
WHERE s3.sepsis3 = TRUE
UNION ALL
SELECT 'Heart Rate', ROUND(AVG(heart_rate_score), 2)
FROM mimiciv_derived.sirs si
INNER JOIN mimiciv_derived.sepsis3 s3 ON si.stay_id = s3.stay_id
WHERE s3.sepsis3 = TRUE
UNION ALL
SELECT 'Respiratory', ROUND(AVG(resp_score), 2)
FROM mimiciv_derived.sirs si
INNER JOIN mimiciv_derived.sepsis3 s3 ON si.stay_id = s3.stay_id
WHERE s3.sepsis3 = TRUE
UNION ALL
SELECT 'WBC', ROUND(AVG(wbc_score), 2)
FROM mimiciv_derived.sirs si
INNER JOIN mimiciv_derived.sepsis3 s3 ON si.stay_id = s3.stay_id
WHERE s3.sepsis3 = TRUE;

Limitations

1. Low Specificity: Many non-infectious conditions trigger SIRS (trauma, surgery, pancreatitis)
2. Sensitivity Issues: Can miss infected patients who don't mount inflammatory response
3. Replaced by Sepsis-3: Current guidelines use SOFA-based Sepsis-3 criteria

References

• Bone RC et al. "Definitions for sepsis and organ failure and guidelines for the use of innovative therapies in sepsis." Chest. 1992;101(6):1644-1655.
• American College of Chest Physicians/SCCM Consensus Conference. Critical Care Medicine. 1992;20(6):864-874.