SIRS criteria
Summary
Systemic Inflammatory Response Syndrome - a clinical syndrome of systemic inflammation defined by >=2 of: temperature, heart rate, respiratory rate, and WBC abnormalities. SIRS + suspected infection historically defined sepsis (now superseded by Sepsis-3/qSOFA but still high-yield).
Detail
Classic SIRS criteria (>=2 of 4): temperature >38 degrees C or <36 degrees C; heart rate >90/min; respiratory rate >20/min or PaCO2 <32 mm Hg; WBC >12,000 or <4,000/mm^3 or >10% bands. Triggers include infection, trauma, burns, pancreatitis, and ischemia. SIRS + infection = sepsis (old definition); sepsis + organ dysfunction = severe sepsis; + refractory hypotension despite fluids = septic shock. The 2016 Sepsis-3 definitions replaced SIRS with qSOFA (RR >=22, altered mentation, SBP <=100) for screening outside the ICU and SOFA score for diagnosis, but SIRS criteria remain commonly tested. Limitations: non-specific (any inflammatory state qualifies) and insensitive in immunosuppressed patients.
Sources
- First Aid for USMLE Step 2 CK
- Harrison's Principles of Internal Medicine
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