**3. Indications for duodenal exclusion**

Duodenal exclusion (DE) can be used as a complement to different procedures. Whereas foregut diversion is the shared element, the final objectives meant to achieve with the exclusion vary according to the operation conducted.

In metabolic surgery, procedures that combine the restriction of food intake and the exclusion of the proximal intestinal segment such as Roux-en-Y gastric bypass (RYGB) and biliopancreatic diversion (BPD) have shown to induce a greater weight loss and higher T2DM resolution rates compared to restrictive procedures without intestinal exclusion [11, 12]. Moreover, the fact that the anti-diabetic effects occur rapidly and are noticeable within days after surgery, implies that these benefits are independent of weight loss or caloric restriction and that exclusion of the foregut produces changes in glucoregulatory mechanisms and glucose homeostasis [3, 13]. The foregut hypothesis [3, 14] suggests that metabolic surgical procedures that exclude the duodenum and proximal jejunum prevent ingested food from activating a diabetogenic signal from these segments of the small intestine thus improving glucose metabolism. The physiologic response to food ingestion is mediated by incretins such as GIP and GLP-1 which promote insulin

secretion. In addition to this incretin effect, nutrients in the gastrointestinal tract activate negative mechanisms mediated by anti-incretin factors to compensate for the glucose-lowering effects of incretins and other postprandial processes. The exertion of a negative effect on insulin makes anti-incretin signals promote insulin resistance and T2DM. Therefore, because of bypassing the upper intestinal tract, the release of these factors is avoided enhancing the action of incretins from the hindgut.

Another indication for DE is severe or complicated peptic ulcer disease (PUD). Despite decreases in its incidence and rates of hospital admission and mortality with the advent of effective pharmacological agents, there is still an estimated prevalence between 5–10% [15]. Alcohol consumption, smoking, long term NSAID use, and the incidence of the Helicobacter pylori infection are all contributing factors. Among the associated complications, bleeding is the most common one, followed by perforation, obstruction, and malignancy. Perforation, although less frequent, is the prevailing indication for emergency surgery causing approximately 40% of all ulcer-related deaths [15, 16]. When the size of the ulcer prevents an adequate primary closure alone, duodenal exclusion with or without resection can be employed. In the case of gastric PUD, distal gastrectomy can be performed if needed with concomitant vagotomy and reconstruction. Duodenal PUD can be managed by simple transection pre- or post- pyloric, thereby excluding the duodenum from alimentation, and reconstruction.

Complex traumatic duodenal injuries (grade III or greater according to the American Association of Surgery for Trauma Organ Injury scale) have also been traditionally treated with duodenal exclusion [17]. The management of these wounds is challenging since they are usually accompanied by associated injuries and have significant mortality and morbidity. Protection of the primary repair by diverting the duodenum may prevent dehiscence and fistula formation with an eventual improvement in patient's outcomes. Initially, the exclusion procedure described by Berne [18] consisted in diverticulizing the duodenum; the duodenal injury was repaired and a vagotomy, antrectomy, gastrojejunostomy, tube duodenostomy, and T tube biliary drainage were done. This technique was effective in excluding the biliary and pancreatic secretions but too complex and time-consuming considering the usually fragile condition of the patient. Therefore, it was substituted with a simpler procedure, introduced by Jordan [19], that shares the same objective of decompression of the duodenum. While maintaining the primary repair of the duodenal injury, it closes the pylorus through a gastrotomy that is used later to place the gastrojejunostomy eliminating the need for gastric resection. A spontaneous opening of the pylorus is seen approximately 30 days after surgery.

In the case of gastric outlet obstruction, either due to benign or malignant conditions, a gastroenteric anastomosis with exclusion of the duodenum and proximal small intestine can be done as a first step in the treatment of the disease or as a palliative measure for inoperable cancers.
