3. Technical requirements for IPAA 3.1 Total colectomy When freeing the colon, attention should be paid to exclude Crohn’s disease or malignant tumors of the small intestine. Unless there is a combination of colorectal tumors, the mesenteric vessels should be ligated and cut as close to the intestinal canal as possible for convenient operation. When freeing the rectum, care should be taken to avoid damage to the ureter and pelvic autonomic nerves: the posterior rectum should be free along the “sacred plane” up to the level of the anal raphe as in the case of total rectal mesorectal resection for rectal cancer. If a portion of the rectal mesentery remains during surgery in children, the rectal mesentery may enlarge in the future and thus interfere with pouch emptying. When freeing the anterior rectal wall, the free layer is located posterior to Denonvilliers’ fascia, as close to the rectum as possible, which helps to protect the autonomic plexus anterior to Denonvilliers’ fascia. The lateral rectal ligaments on both sides should also be cut close to the rectum and continued down to the lower margin of the prostate or the lower third of the vagina, where the rectum is sufficiently free to reach the plane of the anal levator muscle. Finally, the location of rectal dissection is chosen according to the anastomosis. The surgical area is adequately hemostatic, and the dissected resection specimen is examined for the presence of Crohn’s disease or colorectal cancer manifestations. 3.2 Selection and fabrication of IPAA storage pouch The crucial step before making the storage pouch is to determine whether the anastomosis between the storage pouch and the anal canal can be successfully completed. First of all, the length of the small intestine should be ensured, and the disconnected colon and ileum should be as close to the colon as possible. The most accurate way to determine whether the anastomosis of the pouch to the anal canal can be successfully completed is by virtualizing the shape of the pouch and then pulling it to the pelvic floor with one hand and using a double-combination approach with the other hand. The pubic symphysis can also be used as a basis for judgment (the lowest point of the pouch is 6 cm above the pubic symphysis), but sometimes it may not be accurate enough. There are various types of reservoir bag construction, and currently there are mainly J, S and W-type reservoir bags, etc. Regardless of which type of reservoir bag is designed, its main purpose is to reduce the complications of the reservoir bag and improve the function of the reservoir bag. The size of the storage bag is closely related to its postoperative function, the storage bag is too small for poor stool storage function, too large is easy to lead to defecation difficulties. The volume of the bag is usually increased to 2-4 times the initial size 1 year after surgery. In 1980, Utsunomiya et al. proposed the construction of a J-shaped storage bag. This type of storage bag is less technically demanding and easy to construct, and has been widely adopted in recent years. In the construction of the J-shaped storage bag, the end 30-40 cm of the ileum is first folded into two sections, each 15-20 cm, with the shortest not less than 12 cm, and then a small incision is made at the lowest part of the bag, and a linear cutting suture is placed to perform a side-to-side anastomosis of the two ileum sections, followed by a linear cutting closure to close the tip of the J-shaped storage bag, and reinforced with sutures. Finally, the anastomosis was inspected to determine whether there was bleeding, and the integrity of the pouch was determined by irrigation with saline or dilute iodine. Parks and Nicholls first reported hand-anastomosed S-shaped bags. Although the J-pouch is most commonly used, the S-pouch may be a better choice in some cases, such as when the patient has a short mesentery, more adipose tissue, or a deep, narrow pelvis. Compared to the J-pouch, the S-pouch generally provides a longer length of bowel (2-4 cm) with less tethering to the anastomosis site, which helps to reduce anastomotic tension. Three 12-15 cm long segments of terminal ileum are required to create the S-shaped pouch. First, the plasma muscle layer is sutured between the three segments of intestinal collaterals, and then the anterior wall of the intestinal canal is cut in an “S” shape, and the posterior wall and anterior wall are successively sutured, and the anterior wall plasma muscle layer is embedded and injected with saline to test for leakage. The outlet of the S-shaped pouch should be generally shorter than 2 cm. There is also the so-called quadruple intestinal collaterals or W-shaped pouch. To construct this pouch, the end 50 cm of the small intestine is folded into four collaterals, each 12 cm long, forming a W-shaped configuration. Due to the complexity of production, it has been less used clinically. 3.3 Pouch-anal canal anastomosis Pouch-anal canal anastomosis can be done by anastomosis or hand suturing. If the double anastomosis method is used, attention should be paid to straighten the direction of the small intestine to avoid twisting of the small intestine mesentery before the anastomosis is completed. In female patients, care should be taken to avoid inadvertent entrapment of the posterior vaginal wall. During anastomosis, the anastomosis should be placed 2-3 cm above the anal verge, approximately equal to the length of the distal two phalanges of the index finger. This practice can avoid misjudgment of the reservoir pouch-rectal anastomosis due to the high anastomotic position. If manual suturing is used, the anal margin is retracted with a traction line in the 4 quadrants of the anus and placed on an anal pulling hook to avoid excessive retraction of the anal canal that could damage the anal sphincter. When removing all the mucosa under direct vision, care is taken to avoid residual “epithelial islands”. To avoid the occurrence of pouch-vaginal fistula, the suture should not be too deep in the anterior rectal wall of female patients. After completion of the anastomosis, air or saline should be injected through the anus for leak test. 3.4 Comparison of different types of reservoir pouches A Meta-analysis that included 18 studies comparing 1519 patients with J, S, or W type reservoir pouches found no statistically significant differences in postoperative complications including anastomotic leak, anastomotic stricture, pelvic infection, reservoir pouchitis, small bowel obstruction, and reservoir pouch failure among the 3 types of reservoir pouches. In terms of function, J-pouch patients had more bowel movements per day than S- or W-pouch patients. In addition, J-pouch patients used more antidiarrheal agents than S- or W-pouch patients. There was no statistically significant difference in either the number of bowel movements or the use of antidiarrheal agents between S and W storage bag patients. The percentage of patients with difficult bag evacuation requiring intubation was 1.8%, 29.6%, and 20.0% for J, S, and W bag types, respectively. In addition, the incidence of fluid leakage and incontinence was essentially similar in the three types of storage bags. The study showed that good function of the reservoir bag was mainly related to reservoir bag compliance, anal sphincter function, and intact anal reflex, and not directly related to the type of reservoir bag. 3.5 Methods to reduce anastomotic tension The key to successful IPAA is to make the reservoir bag reach the anastomosis tension-free. Successful construction of the storage pouch often requires adequate freeing of the small bowel. Causes of anastomotic tension in IPAA may include: (1) excessive obesity; (2) extensive adhesions from previous abdominal surgery; (3) previous small bowel resection; and (4) the patient’s need for rectal mucosal debridement with manual suturing. Currently, there are several methods to address excessive anastomotic tension, in addition to adequate freeing of the small bowel mesentery up to the root of the superior mesenteric artery at the level of the duodenum, as follows 3.5.1 Storage pouch folding orientation Phillips believes, based on personal observation, that when the storage pouch is not pulled down long enough for anastomosis, an attempt can be made to flip the pouch forward and position the mesentery posterior to the pouch, which provides approximately 0.5 to 1.0 cm more length [36]. 3.5.2 Mesenteric incisions (open windows) To obtain a longer intestinal tube, multiple transverse incisions can be made in the mesentery covering the superior mesenteric artery, both anterior and posterior, with 5 or 6 transverse incisions being sufficient. This approach adds approximately 2 cm to the length and is particularly indicated in patients with a history of previous abdominal surgery resulting in intestinal adhesions and some degree of peritoneal fibrosis. 3.5.3 Mesenteric vessel dissection The length of the mesenteric vessels can also be increased by vessel dissection to achieve a tension-free anastomosis.Smith et al. observed in a study of cadavers that if the end of the mesenteric vessels (or storage pouch) reached 6 cm below the pubic symphysis, the storage pouch was essentially effective in reaching the dentate line and completing a tension-free anastomosis.Martel et al. found that dissection of the superior mesenteric vessels in fresh cadavers The length added to the root mesentery was significantly greater (mean 6.5 cm) than that added to the root mesentery of free ileocolic vessels (mean 3.0 cm). In contrast, Burnstein and colleagues concluded that dissociation of the main mesenteric vessel, the ileocolic artery, is usually unnecessary. Their common practice is to dissociate 2 or 3 small ileo mesenteric vessels between the primary and secondary vascular arches. This practice can add 2 to 5 cm to the length. Goes et al. suggested preserving the right branch of the middle colonic artery and the marginal vascular arches of the right hemicocele and cecum, while dissecting the vessels at the beginning of the right colonic and ileocolic arteries and the distal 1/3 of the main trunk of the superior mesenteric artery to obtain a longer intestinal canal. This approach requires more vessel dissection, takes longer and is more technically challenging, and allows for an average of 11.2 cm of additional length to be obtained. However, this approach may lead to pouch overlap with impaired emptying or prolapse, and may also increase the risk of ischemic infarction of the pouch. 3.6 Hand suture versus instrumented anastomosis IPAA can be accomplished by either hand suture or instrumented anastomosis, and there is still some controversy regarding which approach to take. The core of the controversy is the need to excise the anal transitional zone (ATZ), which is the 0.6-2.0 cm circumferential superior belt above the dentate line, where many somatic nerve endings are present and where post-IPAA pouch cuffing is common. The anastomotic method cuts the rectum at the level of the anorectal loop, preserving 1~2 cm of the mucosa of the anal canal migration zone for insertion of the anastomotic head, thus allowing the sensory epithelium of the anal canal to be preserved while reducing the tension of the anastomosis. The advantages are ease of operation, lower complication rate and better defecation function. The disadvantage is that the epithelium of the metastatic area is preserved and the possibility of malignancy exists. However, the results of a Meta-analysis showed no statistically significant difference in postoperative complications between the two methods. Although the frequency of defecation was similar, fecal incontinence and leakage were more frequent with hand-sutured IPAA. Also, anorectal physiological measurements showed significantly lower resting and tightening pressures in patients with hand-sutured IPAA. The incidence of postoperative sexual dysfunction, quality of life, and incidence of heterotypic growths in the anal canal migration zone were essentially similar between the two. 3.7 Mucosal resection and risk of cancer The benefit of mucosal resection at the time of pouch surgery is still controversial The development of pouch-related tumors in UC patients after IPAA is relatively rare, and there are few cases of tumors occurring in the pouch or residual anorectal mucosa that have been reported in detail in the literature. The cumulative incidence of tumors 20 years after IPAA is generally ≤0.4%. Previous studies have reported that mucosal resection does not eliminate the risk of pouch-associated tumors. Tiny islands of rectal mucosa remain after mucosal resection in approximately 20% of patients, resulting in tumors between the pouch and the muscularis. A Meta-analysis of 3245 North American patients showed a significantly higher incidence of pouch-associated neoplasia after mucosal resection. Overall, it is not certain whether mucosal resection eliminates the risk of tumor development and is therefore less commonly used in general. 3.8 Laparoscopic IPAA and open IPAA The advent of laparoscopic IPAA was an important advancement in this procedure. In 1992, Peters first applied laparoscopic techniques to perform IPAA in patients with UC; however, surgeons were not optimistic about laparoscopic surgery in the early days due to the complex course of chronic disease as well as chronic malnutrition and fragility of the intestinal wall. At the same time, surgeons did not have sufficient experience in laparoscopic colon surgery and appropriate equipment such as specialized anastomoses; the surgical technique of laparoscopic IPAA was also difficult. For these reasons, the practice of IPAA via laparoscopy was not widely used and was limited to a few centers. With the later accumulation of surgical experience and the availability of dedicated laparoscopic surgical equipment, laparoscopic IPAA has gradually become more widely performed. Currently, IPAA is safe and feasible whether performed open or laparoscopically, and a meta-analysis by Ahmed et al. including 11 studies comparing the advantages and disadvantages of both showed that the differences between open and laparoscopic IPAA were not statistically significant in terms of length of stay, complication rates, reoperation rates, readmission rates, and operative mortality. Laparoscopy was more advantageous in terms of cosmetic results and less trauma, however, its operative time was longer. In addition, laparoscopic surgery requires less time for stoma retraction and restoration of bowel continuity, while helping to reduce adhesions at the incision, abdominal or adnexal sites. In female patients, laparoscopic surgery can also reduce the incidence of infertility, with a conception rate of 31% to 73%, which may be related to the reduction of adhesions in the ovaries and fallopian tubes and pelvis with laparoscopic surgery. With the advancement of technology, combined laparoscopic and transanal total mesorectal excision (TaTME) approach to complete IPAA has also emerged in recent years. leo et al. tried the use of transanal total mesorectal excision combined with single-port laparoscopic abdominal surgery in UC patients with IPAA and showed that this approach can be performed as open TaTME avoids repeated use of the anastomosis and allows for safer resection of the low rectum. taTME combined with single-port laparoscopic approach is less invasive, has fewer incisions, reduces postoperative pain, and decreases the incidence of incisional hernias. This technique is still immature, and the prospects of its clinical application need to be further observed. Conclusion: Surgical treatment has become one of the important tools in the treatment of UC, and IPAA is currently the standard procedure of choice for the surgical treatment of UC. This procedure not only can completely remove the diseased bowel segment, but also can preserve the sphincter muscle intact so as to preserve the anal bowel control function and improve the quality of life, so our country should pay more attention to the surgical treatment of UC. Although the operation of IPAA is not complicated, it is still necessary to master the timing and indications of the operation, as well as to be familiar with the details related to the operation and standardize the operation.