Systemic Inflammatory Response Syndrome (SIRS)

Localized inflammation may promote a response with recruitment of inflammatory cells and release of cytokines such as interleukins, tumor necrosis factor, and interferon gamma. Bacterial infections with gram negative organisms can release endotoxins, while gram positive organisms release exotoxins, and either can circulate widely. Ongoing and worsening inflammation can increase the cascade of events producing even more cytokine release and a systemic reaction with counter-inflammatory response syndrome (CARS). When there is extensive activation of inflammation with subsequent release of pro-inflammatory and anti-inflammatory cytokines into circulation, multiple organs may be affected. SIRS is defined as two or more of the following findings:

  • Fever >100.4°F (38°C) or <96.8°F (36°C)

  • Heart rate of >90 beats/min

  • Respiratory rate >20 breaths/min or arterial carbon dioxide tension of <32 mm Hg

  • Abnormal white blood cell count (>12,000/ÁL or <4000/ÁL or >10% immature [band] forms)

SIRS may be initiated by a number of underlying disease processes. Many but not all cases follow from infection with inflammation. However, a generalized inflammatory response may follow an ischemic injury, traumatic injury, or immunologic event. Serum procalcitonin is useful to distinguish infectious from non-infectious etiologies for SIRS.