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Systemic Inflammatory Response Syndrome - Identify inflammatory response to infection or injury
○ Negative - Temperature 36-38°C
○ Negative - Heart rate ≤90 bpm
○ Negative - RR ≤20 and PaCO₂ ≥32 mmHg
○ Negative - WBC 4-12 and bands ≤10%
≥2 of the following criteria must be present:
No SIRS criteria met. Continue standard care. Reevaluate if clinical status changes.
When SIRS (≥2 criteria) occurs with suspected or confirmed infection, consider sepsis diagnosis. Evaluate for organ dysfunction using SOFA score.
SIRS is sensitive but not specific. Many non-infectious conditions cause SIRS. Clinical context essential for interpretation.
| Criterion | Abnormal Values | Clinical Significance |
|---|---|---|
| Temperature | >38°C (100.4°F) or <36°C (96.8°F) | Fever or hypothermia indicate host response to inflammation |
| Heart Rate | >90 beats/min | Tachycardia from increased metabolic demand or cardiovascular stress |
| Respiratory Rate | >20 breaths/min or PaCO₂ <32 mmHg | Tachypnea or hyperventilation causing respiratory alkalosis |
| White Blood Cells | >12,000/μL or <4,000/μL or >10% bands | Leukocytosis, leukopenia, or left shift indicating immune activation |
Sensitive screening tool for systemic inflammation. Prompts clinicians to search for underlying cause and assess disease severity early in clinical course.
When SIRS occurs with infection, raises suspicion for sepsis. Triggers evaluation for organ dysfunction and consideration of sepsis protocols and early treatment.
Historically used to define sepsis in research (Sepsis-1 and Sepsis-2 definitions). Still employed in some protocols though replaced by SOFA in Sepsis-3.
Simple criteria easily assessed in any setting. Can be calculated rapidly without specialized tests, making it practical for diverse clinical environments.
Many benign and non-infectious conditions trigger SIRS. Fever from medications, tachycardia from pain/anxiety, normal pregnancy can all meet criteria without serious pathology.
SOFA score replaced SIRS in 2016 Sepsis-3 definitions for sepsis diagnosis. SOFA better predicts mortality and focuses on organ dysfunction rather than inflammatory markers.
SIRS alone does not indicate severity or need for ICU. Must be interpreted with clinical picture, organ dysfunction assessment, and source of inflammation.
Number of SIRS criteria does not reliably predict outcomes. Patient with 4 criteria from minor cause may fare better than one with 2 criteria from severe sepsis.
SIRS (Systemic Inflammatory Response Syndrome) is defined as the presence of ≥2 of the following: temperature >38°C or <36°C, heart rate >90 bpm, respiratory rate >20/min or PaCO₂ <32 mmHg, and WBC >12,000 or <4,000 or >10% bands. SIRS represents a systemic inflammatory response to various insults, both infectious and non-infectious. It's a sensitive but non-specific indicator of physiologic stress.
No. SIRS alone does not equal sepsis. Under older definitions (Sepsis-1 and Sepsis-2), sepsis was defined as SIRS + suspected or confirmed infection. However, SIRS can result from many non-infectious causes (trauma, burns, pancreatitis, MI). In current Sepsis-3 definitions, sepsis requires evidence of infection plus organ dysfunction (SOFA increase ≥2), moving away from SIRS criteria.
The 2016 Sepsis-3 task force replaced SIRS with SOFA for sepsis diagnosis because SIRS lacked specificity - up to 90% of ICU patients meet SIRS criteria regardless of infection. SIRS also doesn't capture organ dysfunction, which is the hallmark of sepsis. SOFA better identifies patients at risk for poor outcomes and focuses on the life-threatening organ dysfunction that defines sepsis.
SIRS remains useful as a sensitive screening tool for systemic inflammation and to prompt clinical evaluation. However, for sepsis diagnosis and risk stratification, use SOFA or qSOFA as recommended in Sepsis-3. SIRS can alert you to look for underlying problems, but should not solely drive major clinical decisions. Integrate SIRS with other assessments like qSOFA, lactate, and clinical judgment.
Many conditions cause SIRS without infection: major trauma, burns, pancreatitis, myocardial infarction, pulmonary embolism, major surgery, hemorrhagic shock, autoimmune flares, malignancy, and drug reactions. Even normal conditions like pregnancy or vigorous exercise can meet some SIRS criteria. This is why SIRS has poor specificity and requires clinical context for proper interpretation.
SIRS (≥2 of 4 inflammatory criteria) is sensitive but non-specific. qSOFA (3 simple bedside criteria) screens for high-risk patients outside ICU and should prompt SOFA calculation. SOFA (6 organ systems) quantifies organ dysfunction and defines sepsis when increased ≥2 points with infection. Use SIRS for initial screening, qSOFA for rapid risk assessment, and SOFA for sepsis diagnosis and severity tracking.
Standard SIRS criteria are for adults. Pediatric SIRS criteria use age-adjusted cutoffs for temperature, heart rate, respiratory rate, and WBC because normal values vary by age. For example, tachycardia thresholds are higher in infants. Use pediatric-specific SIRS criteria when evaluating children. Sepsis-3 definitions and SOFA/qSOFA also have limited pediatric validation, requiring specialized pediatric tools.
SIRS was introduced in 1992 consensus conference to define the systemic inflammatory response. It formed the basis of sepsis definitions for over 20 years (Sepsis-1 and Sepsis-2). While no longer central to sepsis definitions, SIRS remains a useful concept for recognizing systemic inflammation.
SIRS reflects widespread activation of inflammatory pathways with release of cytokines, complement, and other mediators. This causes fever, tachycardia, tachypnea, and leukocyte changes. The response can be beneficial (fighting infection) or harmful (excessive inflammation causing organ damage).
While replaced by SOFA in Sepsis-3, SIRS retains value as early warning system. Use it to trigger clinical assessment but combine with tools like qSOFA, SOFA, and lactate for risk stratification. Clinical judgment and identification of underlying cause remain paramount.
This SIRS calculator is for educational and informational purposes only. SIRS is a sensitive but non-specific screening tool. It should not be used alone for diagnosis or treatment decisions. SIRS does not equal sepsis. Always integrate with comprehensive clinical assessment, consider organ dysfunction using SOFA, and consult qualified healthcare providers.