Sepsis is a clinical syndrome that complicates severe infection and is characterized by systemic inflammation and widespread tissue injury. A continuum of severity from sepsis to septic shock and MODS exists. The clinical process usually begins with infection, which potentially leads to sepsis and organ dysfunction. [2] A consensus panel of the American College of Chest Physicians and the Society of Critical Care Medicine developed definitions of the various stages of this process (see the image below). [3]

Infection is usually a microbial phenomenon in which an inflammatory response to the presence of microorganisms or the invasion of normally sterile host tissue by these organisms is characteristic. However, viral infections can be indistinguishable from bacteria infections in their presentation.
Bacteremia is the presence of viable bacteria in the blood.
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Stages of sepsis based on American College of Chest Physicians/Society of Critical Care Medicine Consensus Panel guidelines.
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Pathogenesis of sepsis and multiorgan failure.
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Venn diagram showing overlap of infection, bacteremia, sepsis, systemic inflammatory response syndrome (SIRS), and multiorgan dysfunction.
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Acute respiratory distress syndrome (ARDS) present in this chest x-ray (CXR) film is a common organ system affected in multiorgan failure of sepsis.
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Acute respiratory distress syndrome (ARDS) shown in this chest x-ray (CXR) film is a common complication of septic shock. Note bilateral airspace infiltration, absence of cardiomegaly, vascular redistribution, and Kerley B lines.
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Organizing phase of diffuse alveolar damage (ARDS) secondary to septic shock shows diffuse alveolar injury and infiltration with inflammatory cells.
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Organizing diffuse alveolar damage in a different location showing disorganization of pulmonary architecture.
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A high-power view of organizing diffuse alveolar damage (ARDS) shows hyperplasia of type II pneumocytes and hyaline membrane deposits.