DEFINITIONS Sepsis is a complex syndrome that results from a host’s response to infection. Simply put, it is the systemic inflammatory response syndrome (SIRS) arising because of documented or suspected infection. Clinically, SIRS is identified by the presence of at least two of the following: fever or hypothermia, tachycardia, tachypnea, and leukocytosis or leukopenia. Severe sepsis is sepsis with organ dysfunction or tissue hypoperfusion from the infection. Septic shock is severe sepsis plus hypotension that is not corrected by fluid resuscitation. Since 1991, the definitions and diagnostic criteria have expanded with inflammatory, hemodynamic, organ dysfunction, and tissue perfusion variables, but general definitions are the same. Sepsis-related terminology and definitions are in Table 2.1. Diagnostic criteria for sepsis are in Table 2.2. The document by a consensus committee of international experts called “Surviving Sepsis Campaign” has become one of the most comprehensive guidelines for clinicians as to best practice (though not yet standard of care) in the care of patients with severe sepsis and septic shock. EPIDEMIOLOGY The incidence of sepsis, severe sepsis, and septic shock are probably underestimated since most estimates are based on hospital databases that rely on the International Classification of Diseases, and so are biased toward a more severely ill population. The global incidence of sepsis is reported as from 22 to 240 cases/100 000 persons; severe sepsis from 13 to 300 cases/100 000 persons; and for septic shock, 11 cases/100 000 persons (based on a 2012 study). Case-fatality rates are as high as 30% for sepsis, 50% for severe sepsis, and 80% for septic shock. In the United States, the incidence of severe sepsis had been rising but in-hospital mortality was decreasing and not significantly different from Europe.
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