Objective:To define whether the gastric mucosal-arterial PCO2gradient (PCO2gap) reliably reflects hepatosplanchnic oxygenation in septic patients.Design:Prospective observational clinical study.Setting:An adult, 31-bed medical/surgical department of intensive care of a university hospital.Patients:A total of 36 hemodynamically stable, invasively monitored, mechanically ventilated, sedated, paralyzed patients with severe sepsis.Interventions:In each patient, hepatosplanchnic blood flow was determined by the continuous indocyanine green infusion technique and gastric mucosal PCO2by the saline tonometry technique. Suprahepatic venous blood oxygen saturation and PCO2also were measured. The mesenteric veno-arterial PCO2gradient was determined as the difference between the suprahepatic venous blood PCO2and the arterial blood PCO2.Measurements and Main Results:There were significant correlations between the hepatosplanchnic blood flow and the suprahepatic venous blood oxygen saturation (r2= .56;p< .01), between the hepatosplanchnic blood flow and the mesenteric veno-arterial PCO2gradient (r2= .55;p< .01), and also between the suprahepatic venous blood oxygen saturation and the mesenteric veno-arterial PCO2gradient (r2= .64;p< .01). There was no statistically significant correlation between the PCO2gap and the hepatosplanchnic blood flow, the suprahepatic venous blood oxygen saturation or the mesenteric veno-arterial PCO2gradient.Conclusions:In stable septic patients, the PCO2gap is not correlated with global indexes of gut oxygenation. The interpretation of PCO2gap is more complex than previously thought.