Advanced stages of the response to life-threatening infection, severe trauma, or other physiological insults often lead to exhaustion of the homeostatic mechanisms that sustain normal blood pressure and oxygenation. These syndromic presentations often meet the diagnostic criteria of sepsis and/or the acute respiratory distress syndrome (ARDS), the two most common syndromes encountered in the intensive care unit (ICU). Although critical illness syndromes, such as sepsis and ARDS, have separate clinical definitions, they often overlap clinically and share several common injury mechanisms. Moreover, there are no specific therapies for critically ill patients, and as a consequence, approximately 1 in 4 patients admitted to the ICU will not survive. The purpose of this observational study is to identify early patient biologic factors that are present at the time of ICU admission that will help diagnose critical illness syndromes earlier, identify who could benefit most from specific therapies, and enable the discovery of new treatments for syndromes such as sepsis and ARDS.