An experimental part of the study aims at establishing enteric neuronal networks as functional bioassays for the qualitative detection of neurotoxic humoral factors. Human colon samples will be exposed to the serum of critically ill patients with and without CIP in an organ bath (100% serum) under standardized physiologic conditions. Alterations to neuronal functions (contractions, spontaneous activity) will be studied between serum from patients with CIP, without CIP and serum probes from healthy volunteers (without critical illness).