Modeling Postoperative Pathologic Ileus in Mice: A Simplified and Translational Approach

Postoperative Ileus (POI) is an iatrogenic complication characterized by a temporary paralysis of gastrointestinal transit, leading to food intolerance, nausea, vomiting, and thus prolonged hospitalization. The severity of POI is influenced by surgical trauma, particularly in intestinal surgeries, which have a high complication rate. To date, no animal model has precisely replicated POI in the context of digestive sutures or anastomoses, procedures common in human digestive resections.

To induce POI, mice underwent different surgeries. The surgical procedure involved a midline laparotomy, externalization of the small intestine following external manipulation through moistened cotton applicators, mimicking the surgeon's action when searching for an intestinal lesion. An ileo-ileal anastomosis was also performed to ensure relevance to human surgical intervention. Intestinal transit was measured by assessing gastric emptying, gastrointestinal transit time (gavage with charcoal, fecal output), and gut motility (isotonic contraction). Postoperative inflammation is assessed in different tissue layers and areas of theintestine.

The externalization of the small intestine with caecum and manipulation for 10 min induced a pathological postoperative ileus. This simple gesture induced a decrease in intestinal transit comparable to the surgical intervention, ileo-ileal anastomosis. The model showed decreased gastric emptying and reduced ileal muscle contraction, accompanied by neutrophil and monocyte/macrophage infiltration in the external muscularis.

The developed procedure enables inducing postoperative ileus in mice in a very simple and reproducible way that does not require any specific equipment, mimics clinical practice, and reproduces traits of human pathology.