|Sepsis||SIRS in presence of infection|
|Severe Sepsis||Sepsis with organ dysfunction, hypotension, evidence of hypoperfusion. Can be manifested by acidosis, oliguria, acute mental status change, and, I assume, elevated lactate, as well|
|Septic Shock||Sepsis with hypotension despite fluid resuscitation|
|Multiorgan dysfunction||Unable to maintain homeostasis|
Note that SIRS need not occur from an infection. Infectious processes can cause SIRS and, in fact, may be the most common cause. But pancreatitis, trauma, major surgery (a type of trauma), ischemia for any cause including dehydration, and shock, can cause SIRS as well.