Prognostic Value of Fecal Lactate and the Fecal-to-Serum Lactate Gradient in Resuscitation Response Among Critically Ill Patients With Tissue Hypoperfusion: A Prospective Pilot Study.

Tissue hypoperfusion is a central mechanism in the development of organ dysfunction in critically ill patients. Although serum lactate is commonly used as a marker of hypoxia and a target for resuscitation, it may not adequately reflect regional perfusion, particularly in the splanchnic circulation. Persistent splanchnic hypoperfusion contributes to intestinal barrier dysfunction, bacterial translocation, and progression to multiple organ failure.

This study is based on the hypothesis that, under ischemic conditions, the intestinal mucosa behaves as a semipermeable membrane, allowing equilibration of lactate produced in the intestinal wall into the lumen. Therefore, fecal lactate may serve as a direct and early marker of intestinal hypoperfusion.

This is a prospective, observational, single-center cohort study conducted in an intensive care unit. Adult patients (≥18 years) with evidence of tissue hypoperfusion will be included. Fecal samples will be collected within the first 12-24 hours and processed through dilution, homogenization, centrifugation, and colorimetric analysis of the supernatant to quantify L-lactate levels. Simultaneously, serum lactate will be measured, and the fecal-to-serum lactate gradient will be calculated.

The primary outcome is poor response to resuscitation at 24 hours, defined as a composite endpoint including increased vasopressor requirements, serum lactate clearance <10% or persistent lactate >2 mmol/L, worsening organ dysfunction measured by SOFA score (increase ≥1 point), or death.

Secondary objectives include evaluating the correlation between fecal lactate and organ dysfunction severity, as well as determining the optimal cut-off value for fecal lactate to predict adverse outcomes using receiver operating characteristic (ROC) curve analysis.