Fecal Lactate and Resuscitation Outcomes in Critical Illness

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.

This study aims to identify fecal lactate as a non-invasive, early, and specific biomarker of splanchnic hypoperfusion, potentially improving clinical decision-making and guiding resuscitation strategies in critically ill patients.

Inclusion criteria

• Adult patients ≥18 years admitted to the intensive care unit (ICU)
• Evidence of tissue hypoperfusion defined by at least ONE of the following: Arterial serum lactate ≥2.0 mmol/L or Hypotension requiring vasopressors to maintain mean arterial pressure (MAP) ≥65 mmHg
• Clinical signs of hypoperfusion (capillary refill time >3 seconds or mottling score ≥2)
• Availability of fecal sample within the first 24 hours of ICU admission

Exclusion criteria

• Active gastrointestinal bleeding
• Recent abdominal surgery (<48 hours) with intestinal resection or stoma
• Confirmed Clostridioides difficile infection
• Do-not-resuscitate (DNR) orders at ICU admission