Unifying Concepts

Definitions for the Terms Bacteremia, Sepsis, Severe Sepsis, Septic Shock, and Other Related Disorders

A 1992 American College of Chest Physicians/Society of Critical Care Medicine consensus panel defined the following terms which are relevant to the discussion of septic shock:

Infection: Infection is a microbial phenomenon characterized by an inflammatory response to the presence of microorganisms or the invasion of normally sterile host tissue by those organisms.

Bacteremia: Bacteremia refers to the presence of viable bacteria in the blood.

Systemic inflammatory response syndrome: Systemic inflammatory response syndrome (SIRS) is a widespread inflammatory response to a variety of severe clinical insults. This syndrome is clinically recognized by the presence of two or more of the following:

  • Temperature >38 °C or <36 °C
  • Heart rate >90 beats/min
  • Respiratory rate >20 breaths/min or PaCO2 <32 mmHg
  • WBC >12,000 cells/mm3, <4000 cells/mm3, or >10 percent immature (band) forms

Sepsis: Sepsis is the systemic response to infection. Thus, in sepsis, the clinical signs describing SIRS are present together with definitive evidence of infection.

Severe sepsis: Sepsis is considered severe when it is associated with organ dysfunction, hypoperfusion, or hypotension. The manifestations of hypoperfusion may include, but are not limited to, lactic acidosis, oliguria, or an acute alteration in mental status.

Septic shock: Septic shock is sepsis with hypotension despite adequate fluid resuscitation. It includes perfusion abnormalities such as lactic acidosis, oliguria, or an acute alteration in mental status. Patients receiving inotropic or vasopressor agents may not be hypotensive at the time that perfusion abnormalities are measured.

Hypotension: Hypotension is defined as a systolic BP of <90 mmHg or a reduction of >40 mmHg from baseline, in the absence of other causes for the fall in blood pressure.

Multiple organ dysfunction syndrome: Multiple organ dysfunction syndrome (MODS) refers to the presence of altered organ function in an acutely ill patient such that homeostasis cannot be maintained without intervention. The multiple organ dysfunction syndrome is classified as either primary or secondary.

  • Primary MODS is the result of a well-defined insult in which organ dysfunction occurs early and can be directly attributable to the insult itself (eg, renal failure due to rhabdomyolysis).
  • Secondary MODS is organ failure not in direct response to the insult itself, but as a consequence of a host response. In the context of the definitions of sepsis and SIRS, MODS represents the more severe end of the spectrum of severity of illness characterized by SIRS/sepsis.



  1. American College of Chest Physicians/Society of Critical Care Medicine Consensus Conference: definitions for sepsis and organ failure and guidelines for the use of innovative therapies in sepsis. Crit Care Med. 1992 Jun;20(6):864-74. [Medline]
  2. Angus DC, van der Poll T. Severe sepsis and septic shock. N Engl J Med. 2013 Aug 29;369(9):840-51. [Medline]


Created: Feb 21, 2006
Update: Sep 28, 2014

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