Impact of Ambulatory Physiological Stimulation of the Efferent Limb Prior to Ileostomy Closure on Colorectal Microbiota Composition and Histopathological Findings

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BACKGROUND Loop ileostomies are a type of stoma frequently used to protect high-risk colorectal anastomoses (surgical reconnection of the intestines), for example following rectal cancer resection. Temporary diversion of intestinal transit does not reduce the risk of anastomotic failure, but it does lower the morbidity and mortality associated with potential pelvic sepsis. Unfortunately, a second surgical procedure is required to restore intestinal continuity, and this carries its own risk of complications, the most common being postoperative ileus (temporary paralysis of bowel motility associated with abdominal distension, absence of bowel movements, nausea, and vomiting), which occurs in up to 20% of cases. Several strategies have been proposed to reduce this problem, including stimulation of the efferent limb of the ileostomy (the part that is connected to the unused colon). This intervention consists of instilling a substance through the efferent limb of the ileostomy into the colon, simulating natural intestinal transit. It emerged as a harmless alternative aimed at reversing changes in the excluded colon in preparation for restoration of intestinal continuity. Several Spanish studies have investigated this technique, concluding that it is safe and significantly reduces the rate of postoperative ileus, thereby shortening hospital stay. Regarding the mechanism by which this intervention may be effective, there are studies investigating the changes that occur during diversion of intestinal transit: 1. Histopathology: reduced muscular contractility and the presence of intestinal villi in the efferent intestinal limb and excluded colon, which improve once intestinal flow is restored. 2. Microbiome: significant loss of microbiota in the defunctionalized colon, which progressively recovers with natural intestinal transit and reintroduction of a fiber-rich diet. Structural and microbiota-related changes favor the development of diversion colitis, a condition associated with erratic bowel habits once intestinal transit is restored. In an attempt to reverse this condition, several products have been tested for stimulation of the efferent limb of the ileostomy: probiotics, short chain fatty acids, saline solution with a thickening agent, and the patient's own intestinal contents, a well-tolerated and effective technique, in some cases superior to saline-based alternatives. Overall, the available evidence is of low quality due to the limited number of patients studied and protocol variability. For this reason, we propose the implementation of a protocol for stimulation of the distal ileostomy limb prior to ileostomy closure, either with saline solution and thickening agent (the most widely described technique in the literature) or physiological stimulation using the patient's own intestinal contents. The protocol consists of several sessions in which the instilled volume is progressively increased. This intervention will be performed on an outpatient basis, once daily, during the two weeks prior to surgery. This process promotes the onset of bowel movements through the anus, which progressively become more formed and less frequent, approaching a more normal bowel habit. Only minor adverse effects have been described with this technique, including cramp-like abdominal pain in 27.6% of sessions. Recently, a nationwide study confirmed the favorable clinical outcomes following distal ileostomy limb stimulation before ileostomy closure. However, to our knowledge, no studies have evaluated its effect on intestinal microbiota. HYPOTHESIS Distal limb stimulation of the ileostomy before its closure helps in the recovery of the colorectal microbiome and tissue. This associates with lower postoperative complications, specially postoperative ileus. OBJECTIVES To gain knowledge regarding changes in intestinal microbiota composition before and after stimulation, in order to better understand recovery of intestinal function following this procedure. We will also analyze outcomes after ileostomy closure following efferent limb stimulation, determining the incidence of postoperative complications, particularly postoperative ileus. METHODOLOGY Patients will be randomly assigned to one of three groups: 1. Control (no intervention other than the usual preoperative protocol) 2. Stimulation with serum and thickener 3. Stimulation with own stoma output Samples will be collected in all patients: 1. Stoma output 2. Stool, before stimulation, if performed 3. Stool, after stimulation, if performed 4. Stool, a month after surgery For a group of patients, the ones recruited at Hospital Clínic, rectal biopsies will also be collected before and after stimulation, to compare the effect of the treatment in the colonic tissue. We will collect clinical data during the whole process regarding postoperative complications.

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