The document defines the criteria for systemic inflammatory response syndrome (SIRS), sepsis, severe sepsis, and septic shock. SIRS is a physiological response to inflammation from any source and requires at least two of four criteria. Sepsis is diagnosed when SIRS is present along with a suspected or documented infection. Severe sepsis occurs when sepsis is accompanied by organ dysfunction or hypoperfusion. Septic shock is diagnosed when sepsis criteria are met and hypotension persists despite fluid resuscitation.