Sepsis is a clinical syndrome that complicates severe infection. It is characterized by the cardinal signs of inflammation (vasodilation, leukocyte accumulation, increased microvascular permeability) occurring in tissues that are remote from the infection. Systemic inflammatory response syndrome (SIRS) is an identical clinical syndrome that complicates a noninfectious insult (eg, acute pancreatitis, pulmonary contusion). Current theories about the onset and progression of sepsis and SIRS focus on dysregulation of the inflammatory response, including the possibility that a massive and uncontrolled release of proinflammatory mediators initiates a chain of events that lead to widespread tissue injury. This response can lead to multiple organ dysfunction syndrome (MODS), which is the cause of the high mortality associated with these syndromes.
The definitions, epidemiology, risk factors, and outcomes of sepsis and SIRS are reviewed here. The pathophysiology and treatment of sepsis are discussed separately. (See "Pathophysiology of sepsis" and "Evaluation and management of severe sepsis and septic shock in adults".)
Systemic inflammatory response syndrome (SIRS), sepsis, severe sepsis, and septic shock were initially defined in 1991 by a consensus panel convened by the American College of Chest Physicians (ACCP) and Society of Critical Care Medicine (SCCM) . These definitions were reconsidered in 2001 during an International Sepsis Definitions Conference that included representatives from the ACCP, SCCM, American Thoracic Society (ATS), European Society of Intensive Care Medicine (ESICM), and Surgical Infection Society (SIS), and again in 2012 by the SCCM and ESICM [2,3]. A practical modification of the definitions has been published, which provides exact hemodynamic definitions for sepsis and septic shock .
SIRS is a clinical syndrome that is a form of dysregulated inflammation. The term SIRS has routinely been associated with both infectious processes (sepsis) and noninfectious insults, such as an autoimmune disorder, pancreatitis, vasculitis, thromboembolism, burns, or surgery. SIRS was previously defined as two or more abnormalities in temperature, heart rate, respiration, or white blood cell count . However, in practice, its clinical definition and pathophysiology are equivocal such that SIRS and early sepsis cannot be readily distinguished. Thus, when SIRS is suspected it should prompt an evaluation for a septic focus.
The definitions that we provide below are based upon these resources and represent a continuum of early infection through multiple organ dysfunction syndrome (MODS).