Table 1

Definitions of systemic inflammatory response syndrome (SIRS), infection, sepsis, severe sepsis and septic shock13

SIRS	The systemic inflammatory response to a variety of severe clinical insults. The response is manifested by two or more of the following conditions: temperature >38.3°C or <36.0°C heart rate >90 beats per min respiration >20 breaths/min or PaCO₂ <32 mm Hg white cell count >12×10⁹/L or <4×10⁹/L or >10% bands
Infection	Microbial phenomenon characterised by an inflammatory response to the presence of microorganisms or the invasion of normally sterile host tissue by those organisms.
Sepsis	A systemic response to infection manifested by two or more of the following conditions: temperature >38.3°C or <36.0°C heart rate >90 beats per min respiration >20 breaths/min or PaCO₂ <32 mm Hg white cell count >12 ×10⁹/L or < 4×10⁹/L or >10% bands
Severe sepsis	Sepsis associated with organ dysfunction, hypoperfusion or hypotension. Hypoperfusion and perfusion abnormalities may include, but are not limited to, lactic acidosis, oliguria or an acute alteration in mental status.
Septic shock	Sepsis associated with organ dysfunction, hypoperfusion or hypotension. Hypoperfusion and perfusion abnormalities may include, but are not limited to, lactic acidosis, oliguria or an acute alteration in mental status. Patients on vasopressors may not be hypotensive at the time that perfusion abnormalities are measured.