Short bowel syndrome

　　There are many causes of short bowel syndrome, and adult short bowel syndrome is caused by repeated resection of the small intestine due to recurrent diseases such as Crohn's disease, radioactive intestinal injury, or recurrent intestinal obstruction and intestinal fistula, or due to vascular diseases such as mesenteric vessel occlusion, acute intestinal torsion, or traumatic vascular rupture and occlusion, where a large amount of small intestine is resected due to ischemic necrosis. In extremely rare cases, there may be medical errors in the treatment of peptic ulcer disease, where gastrojejunal anastomosis is performed, resulting in iatrogenic clinical symptoms similar to those after extensive small bowel resection. In children, it is mostly due to congenital factors, such as abdominal rupture, intestinal atresia, and necrotizing enterocolitis, which lead to insufficient small intestine length to maintain adequate absorption of nutrients.

　　1. Adults

　　There are many different causes of short bowel syndrome in adults, mainly due to mesenteric vascular thrombosis or thrombosis, as well as extensive small bowel resection (75% or more) caused by acute intestinal torsion. Factors causing mesenteric vascular thrombosis or thrombosis include: advanced age, long-standing congestive heart failure, atherosclerosis, and heart valve disease, long-term use of diuretics, hypercoagulable state, oral contraceptives; patients with pathologic obesity may also develop symptoms of short bowel syndrome after short-circuiting surgery of the jejunum and ileum. Less common causes of short bowel syndrome include: abdominal injury, primary or secondary intestinal tumors, radioactive intestinal lesions; extremely rare cases include: medical errors in the treatment of peptic ulcer disease, where gastrojejunal anastomosis is performed, producing clinical symptoms similar to extensive small bowel resection.

　　2, Children

　　The causes of short bowel syndrome in children can be divided into prenatal and postnatal causes. The main prenatal cause is small bowel atresia, malrotation of the midgut leading to ectopic fixation or abnormal torsion of the small intestine, which can occur in utero or at any time after birth; necrotizing enterocolitis in the neonatal period is gradually increasing and has been considered to be the main cause of neonatal short bowel syndrome. In addition, less common factors after birth include congenital megacolon affecting the small intestine, mesenteric vascular thrombosis or thrombosis, radiation enteritis, or Crohn's disease, which can also lead to this syndrome, but mainly exist in children of older age groups.

　　If patients with short bowel syndrome do not receive special nutritional support treatment, they will gradually develop symptoms of malnutrition, including weight loss, fatigue, muscle atrophy, anemia, hypoalbuminemia, anemia, hyperkeratosis of the skin, muscle spasms, poor coagulation function, and bone pain. Deficiencies of calcium and magnesium can enhance the excitability of nerves and muscles and cause tetany of the hands and feet. Long-term calcium deficiency can also lead to osteoporosis.

　　The long-term complications of short bowel syndrome include fatty liver, bile duct stones, urinary system stones, and so on.

　　Short bowel syndrome is mainly characterized by early diarrhea and severe nutritional disorders in the later stage. The symptoms of short bowel syndrome are generally divided into three stages: decompensation stage, compensation stage, and late compensation stage. The decompensation stage, also known as the first stage, refers to the early stage after a large amount of small intestine is removed. The remaining intestine not only cannot absorb water and nutrients but also loses digestive juices secreted by the stomach, bile duct, and pancreas. Patients may experience varying degrees of diarrhea, with most patients not very severe. A few patients may have up to 2L of diarrhea per day, and the potassium content in the loose stools can reach 20mmol/L, leading to water, electrolyte, and acid-base disorders as well as acid-base imbalance. The compensation stage, also known as the second stage, is when the body's homeostasis is stabilized after treatment, the frequency of diarrhea decreases, the function of the small intestine begins to compensate, the absorption function is enhanced, the loss of intestinal fluid gradually decreases, and the intestinal mucosa appears hyperplastic. The duration of this stage varies with the length of the remaining small intestine, the presence or absence of the ileocecal valve, and the compensatory function of the intestine, and can last up to 2 years, usually around 6 months. The late compensation stage, also known as the third stage, is when the intestinal function has certain digestive and absorptive functions after compensation. At this time, the mode and amount of nutritional support have been established, but it is necessary to continue maintaining nutrition and preventing complications. The clinical process of short bowel syndrome goes through three stages:

　　1. Acute period: Generally, it manifests within 1 to 3 months after surgery, due to massive diarrhea leading to fluid and electrolyte loss, imbalance, and in severe cases, it can threaten the patient's life. It reaches its peak in 2 to 3 weeks, with up to 2.5 liters or even 5 liters of fluid lost in feces daily. In addition to diarrhea, there are symptoms such as fatigue, oliguria, and dehydration, electrolyte deficiency, acid-base imbalance, hypocalcemia, hypomagnesia, and convulsions.

　　2. Adaptation period: It is a stage of initial oral intake and gradual increase in intake, usually lasting several months to one year. During this period, diarrhea is significantly reduced, water and electrolyte imbalance is somewhat alleviated, and the most prominent clinical manifestation is malnutrition, weight loss, and in severe cases, hypoproteinemia and edema. It can also occur due to vitamin and mineral deficiency, such as night blindness, peripheral neuritis, hemorrhagic tendency due to coagulation disorders, anemia, and osteomalacia.

　　3. Remission period: Generally, it takes about a year after surgery to present a stable state, as the remaining intestinal tract has been able to compensate to the maximum extent, the condition gradually stabilizes, and it can maintain a relatively normal family life, but there may still be manifestations of deficiency of fat-soluble vitamins, calcium, and other trace elements. Excessive resection of the ileum can lead to a deficiency of vitamin B12 in patients. Some patients may not reach the stage of complete oral nutrition, and need to rely on home parenteral nutrition.

　　Short bowel syndrome seriously affects the daily life of patients, so it should be actively prevented. Avoiding excessive resection of the small intestine during surgery is the key to preventing the occurrence of short bowel syndrome. Once it occurs, active rehabilitation treatment and prevention of complications should be carried out.　

　　The diagnosis of short bowel syndrome mainly relies on medical history and clinical manifestations. The main clinical examination methods are as follows:

　　1. Routine blood test: Patients may have iron deficiency anemia or megaloblastic anemia.

　　2. Blood biochemical examination: There may be electrolyte disturbance and acid-base imbalance, negative nitrogen balance; plasma protein and lipids are reduced, and the content of lipids increases.

　　3. Prothrombin test: It can be reduced.

　　4. Absorption test of small intestine for sugar, protein, and fat: All can be reduced.

　　5. Pancreatic function tests and uric acid excretion determination can be performed if necessary.

　　6. In cases of suspected small intestinal contamination syndrome, small intestinal fluid bacterial culture and counting can be performed, and a positive result is obtained if the count exceeds 10^7/ml.

　　7. X-ray barium meal examination: It can clearly determine the length of the remaining small intestine, the time of passage of intestinal contents, the condition of intestinal mucosal folds, and comparative observation can be made through repeated examinations.

　　Early patients with short bowel syndrome often cannot eat by mouth and need to be supplied with energy through parenteral nutrition. When the intestines enter the compensation period, the amount of diarrhea is controlled, and the intestinal function is initially restored, small amounts of isotonic, easily absorbable enteral nutrition preparations can be used, and the dosage can be gradually increased according to the patient's adaptation and absorption. Continuous infusion is conducive to absorption and reduces the acceleration of intestinal peristalsis caused by push-in method. It is expected that enteral nutrition will be given for more than 4 weeks, or if the patient is difficult to tolerate the discomfort of placing a nasogastric tube, percutaneous endoscopic gastrostomy or percutaneous endoscopic jejunostomy can be performed. At the same time, as the nutritional status gradually improves, enteral nutrition can be gradually reduced until it is fully applied. After the enteral nutrition is well adapted, special oral nutritional supplements can be added based on the patient's remaining intestinal length and compensation, and attention should be paid to adding vitamins, trace elements, and supplementing electrolytes. The transition from enteral nutrition to daily diet also needs to be gradual and not rushed. The time it takes for intestinal compensation to tolerate intestinal nutrition without the need for parenteral nutrition is generally 3 to 6 months, and it may also take longer.

　　1. When the intestinal function is initially restored, low-protein, low-fat liquid foods should be chosen, such as thin rice porridge, thin lotus root powder, fruit juice water, vitamin sugar water, carrot water, etc., 50 to 100 ml each time, 3 to 6 times a day.

　　2. When the intestinal function is further restored, nutritionally balanced intestinal nutrition preparations can be selected, such as Ansu, Lishikang, etc.

　　3. Foods to avoid (or reduce) by patients: High-fat, high-fiber, spicy and irritant foods, such as animal fats, celery, spinach, chives, garlic, chili, etc.

　　The treatment of short bowel syndrome adopts different treatment strategies according to its clinical stages: in the acute phase, parenteral nutrition and maintaining electrolyte and water balance are the main methods; in the adaptation period, combined treatment with parenteral nutrition and gradually increasing enteral nutrition is adopted; in the maintenance period, the patient gradually transitions to enteral nutrition as the main method.

　　First, non-surgical treatment

　　1. Acute phase:

　　(1) Maintaining the body's water, electrolyte and acid-base balance and nutrition: It is necessary to carefully record the water intake and output for 24 hours, the results of continuous plasma electrolyte tests, and the weight loss situation, as the basis for supplementing water, electrolytes, and nutrients. The fluids supplemented within 24 to 48 hours after surgery should mainly be saline and glucose solutions, and a certain amount of amino acids and water-soluble vitamins can also be given. The supply of nitrogen sources should start with a small amount and gradually increase the intake of amino acids to correct the negative nitrogen. 6 to 8 liters of fluids should be supplemented daily, and the dosage of electrolytes should be determined according to the monitoring results. Total parenteral nutrition (TPN) can be started 2 to 3 days after surgery, with ingredients including sugar, protein, fat, electrolytes, fat-soluble vitamins A, D, E, and water-soluble vitamins (B1, B2, PP, B6, folic acid, B12, C), trace elements, etc. The required calories and protein should be carefully calculated based on the patient's weight, clinical condition, and level of activity. Calories are mainly provided by glucose and fat, and excessive glucose can be converted into fat and deposited in the liver, increasing the risk of liver failure.

　　(2) Prevention and Treatment of Infection: Antianerobic and aerobic bacteria antibiotics should be chosen for the possibility of enteric infection. When the patient has persistent fever, timely B-ultrasound or CT examination should be performed to detect abdominal abscesses early and treat them effectively.

　　(3) Control of Diarrhea: Fasting and parenteral nutrition can suppress gastrointestinal motility and secretion, delay gastrointestinal emptying, and thereby alleviate the severity of diarrhea. For patients with severe diarrhea that is difficult to control, somatostatin and synthetic analogs such as octreotide 50mg, 2-3 times a day, can be administered subcutaneously to significantly suppress gastrointestinal secretion, alleviate diarrhea, and reduce the loss of electrolytes.

　　(4) Inhibition of Excessive Gastric Acid Secretion: After surgery, excessive gastric acid secretion can be treated with H2 receptor blockers or proton pump inhibitors such as famotidine, Losec, etc., and can also prevent stress ulcers and anastomotic ulcers.

　　2. Adaptation Period:

　　The remaining intestinal tract begins to show compensatory changes, and the frequency of diarrhea tends to decrease. During this period, the focus is to ensure sufficient nutrient intake while gradually replacing intravenous nutrition with enteral nutrition to prevent the reduction of enzymatic activity at the brush border of the small intestinal mucosa. Generally, elemental diet can be used as a transitional measure. The patient needs to use a silicone tube with an outer diameter of 1-2mm and undergo gastrointestinal intubation. If a jejunostomy tube has been placed in advance, feeding can be done through this route. Infusion starts from a 1/4 concentration, with 25ml per hour. The concentration and volume can be gradually increased without exacerbating diarrhea. Gravity drip is usually sufficient. Commercially available elemental diets are very convenient, with 80g dissolved in 300ml of water, producing 4.184kJ of energy per 1ml. The nutritional fluid dose for adults can reach 2000-3000ml. With the increase in elemental diet dosage, intravenous nutrition is gradually reduced and finally withdrawn. Some elemental diets contain amino acids such as glutamine, which play a very important role in promoting the adaptive compensation of the remaining small intestine. Monitoring of relevant laboratory items should still be carried out during this period.

　　During the gradual recovery of the patient's appetite, it is advisable to resume oral feeding as soon as possible. A diet with low fat and moderate carbohydrates, rich in protein and low in residue, can be provided. It is best to make it delicious and appetizing, with small meals and frequent eating. Feeding techniques should be emphasized, as they can achieve twice the results with half the effort, especially important in infants and young children. To prevent insufficient fat intake, medium-chain fatty acids (MCT) can be used instead of ordinary fats, as the former can be absorbed without the need for micelle formation.

　　If diarrhea has been controlled, gradually increase the usual fat intake and add pancreatic lipase to aid digestion and absorption. Such patients are not easily digestible and absorbable to lactose, so dairy products should be gradually increased.

　　If the patient still has excessive gastric acid secretion, continue to administer cimetidine, which can reduce gastric acid secretion and the concentration of hydrogen ions in the small bowel lumen, helping to improve the absorption of fatty acids, proteins, and carbohydrates.

　　At this stage, it is also necessary to pay attention to the supplementation of vitamins, especially fat-soluble vitamins and vitamin B12. Patients are generally prone to calcium deficiency and should be supplemented extra. Other minerals such as magnesium and iron should also be supplemented. Medications containing a variety of vitamins and minerals can be taken. If there is small bowel overgrowth syndrome, oral broad-spectrum antibiotics can be given. At the same time, this stage should also pay special attention to complications caused by parenteral nutrition, such as sepsis caused by catheter contamination, liver disease caused by excessive liver load, and excessive proliferation of bacteria in the small bowel, which need to be actively prevented and treated.

　　3. Maintenance period:

　　At this stage, the residual small bowel function has been maximally compensated, and it is usually able to tolerate oral food without restriction of fat and separation of liquid and solid. However, 30% of patients still have malabsorption phenomena at this stage, and regular determination of plasma vitamin, mineral, and trace element concentrations and supplementation and adjustment treatment are required. If short bowel syndrome that cannot be improved with non-surgical treatment still exists, surgical treatment should be considered.

　　Second, surgical treatment:

　　When severe short bowel syndrome or long-term no improvement in small bowel adaptation after drug, food, nutritional rehabilitation, and TPN treatment, consider surgical treatment. The purpose of surgical treatment is to increase the absorption area of the small bowel or slow down the bowel transport time (delaying the emptying of chyme) to increase the absorption capacity of the small bowel.

　　1. Surgical methods to slow down bowel transport:

　　(1) Inversion of small bowel segments: To invert and anastomose a segment of small bowel, so that the inverted bowel segment exhibits retrograde peristalsis, which can slow down bowel transport and change muscle electrical activity, benefiting the absorption of nutrients. The ideal length of the inverted segment for adults is 10-15 cm, for infants 3 cm, and the inverted segment is the distal small bowel. When the remaining bowel segment of the patient is too short and cannot provide 10 cm of bowel segment for inversion, this operation should not be performed.

　　(2) Intersigmoid coloplasty: Utilizing the characteristics of slow colonic peristalsis and rare segmental peristaltic thrusts, the colon is interposed between the jejunum and ileum to extend the time of bowel transport. There are two types of surgical methods: one is the same-direction peristaltic intersigmoid colon, with 11 cases reported in infants abroad, of which 4 cases were effective; the other is the opposite-direction peristaltic intersigmoid colon, which is similar to the small bowel intersigmoid colon and the effect is not certain. There is no standard length for the interposed colon, and the range is about 8-24 cm.

　　(3) Reconstruction of small bowel valvulae or sphincter: Patients with extensive resection of the small bowel and excision of the ileocecal junction have a very poor prognosis. This surgical procedure is mainly designed for such cases. The general surgical site is at the end of the remaining small bowel, including a nipple-like flap similar to ileostomy, longitudinal muscle incision to allow smooth contraction of the circular muscle, submucosal tunnel of the small bowel, and end-to-end anastomosis of the distal small bowel. Most of these procedures will produce some degree of mechanical bowel obstruction, which can slow down bowel transport and can also prevent excessive growth of bacteria in the small bowel due to retrograde reflux of colonic contents.

　　2. Surgical methods to increase the surface area of the intestinal tract:

　　(1) Jejunoconstriction and elongation: One of the adaptive changes after extensive intestinal resection is the expansion of the remaining intestinal segments, leading to intestinal content stasis and excessive bacterial growth, thereby aggravating malabsorption. Therefore, the narrowing and expansion of the intestinal segments should be able to improve the peristalsis of the small intestine. The technique proposed by Bianchi is to cut a segment of the small intestine along its long axis into two parts, and pay attention to separating the mesenteric blood vessels to maintain their blood supply, and then suture them into two thin intestinal tubes, half the diameter of the original intestinal tube, and twice the length. This surgical method is suitable for patients with intestinal segment expansion, especially children, but there are potential complications such as multiple adhesions and strictures at the anastomotic site.

　　(2) Growth of new jejunal mucosa: An incision is made on the jejunum, and then a colon patch is made from an intact colon, or a colon serosa, abdominal wall muscle flap, or prosthetic material is used to repair a full-thickness intestinal wall defect. The mucosa grows from the edge of the jejunum and covers the mucosa of the colon. Digestive absorption enzymes are produced on the new mucosa, and their secretion volume can be equal to that of the original jejunum mucosa. However, this method is still only used in animal experiments, and the surgical process is also affected by the location of the jejunum, repair materials, and growth factors.

　　3. Intestinal Transplantation:

　　Intestinal transplantation is the most ideal and effective method for treating short bowel syndrome, and it is suitable for patients who need to permanently rely on TPN. However, due to the high mortality rate, rejection reactions and other complications, it has not yet been widely used in clinical practice. Abroad, some cases have been treated with this surgery, and some authors have performed jejuno-hepatic combined transplantation, with the success rate of surgery still not ideal. A group of 71 cases reported in the United States showed that after 2 years of follow-up, 51% of the cases were still alive, some of which had already removed the transplanted jejunum and/or still relied on TPN. Many issues in intestinal transplantation still need to be explored.

　　There are many surgical methods for short bowel syndrome, such as jejunoconstriction and folding, Kimura technique, jejuno-epicardial pacing, jejuno-relooping, and jejuno-sequence elongation, all of which have their indications. However, each method has many complex complications and its effects are not constant, so careful consideration is needed before implementation.