This study evaluates the prognostic value of fecal lactate and the fecal-to-serum lactate gradient as early biomarkers of tissue hypoperfusion in critically ill patients. While serum lactate is widely used, it may not accurately reflect splanchnic perfusion. This prospective observational study aims to determine whether fecal lactate levels obtained within the first 12-24 hours can predict poor response to resuscitation at 24 hours. The primary outcome is a composite of increased vasopressor requirements, persistent hyperlactatemia, worsening organ dysfunction, or death.