The normal length of small bowel in an adult, starting from the duodenojejunal flexure, measures between 275 to 850 centimeters. Around 9 liters of fluid passes through the small bowel daily in the form of oral fluids, saliva, gastric, biliary, and pancreatic secretions. On average, about 7 liters of those fluids are absorbed in the small bowel and 2 liters in the large bowel. The large, healthy bowel absorbs roughly 150 kilocalories per day but can absorb up to 1000 kilocalories per day in those patients with malabsorption.
The absorption of most nutrients occurs in the first 100 centimeters of the jejunum. B12 and bile salts are absorbed in the last 100 centimeters of the ileum; magnesium is absorbed in the terminal ileum and proximal colon; water and sodium absorption occur throughout the bowel.
Short bowel syndrome (SBS) in adults is defined as less than 180 to 200 centimeters of remaining small bowel leading to the need for nutritional and fluid supplements. Although there is no accepted definition for SBS in children, the need for intravenous supplementation when having less than 25% of remaining small bowel that is expected for gestational age has been suggested.
About 75% of cases of SBS develop after a single, massive resection of bowel; whereas, the remaining 25% occur after multiple resections. Around two-thirds of patients who develop SBS survive their initial hospitalization, and a similar number survive their first year after developing SBS. Age and underlying disease primarily determine a patient's long-term outcome.[1][2][3]
SBS can result from extensive surgical resection or congenital intestinal diseases. The most common pathologies that lead to SBS in adults are Crohn disease, mesenteric ischemia, radiation enteritis, post-surgical adhesions, and post-operative complications. In children, the most common pathologies include volvulus, intestinal malformations, and necrotizing enterocolitis.[1]
The epidemiology of SBS is not well-delineated as there are no data on the frequency of intestinal failure secondary to SBS.
SBS can be classified by anatomical, pathophysiological, and postoperative criteria. Anatomically, there are three types of SBS: end-jejunostomy, jejunocolonic anastomosis where the jejunum is in continuity, most commonly, with the left colon, and jejunoileal anastomosis. The pathophysiological criteria can also be subdivided into categories where the colon is in continuity and those where it is not.
The primary pathophysiological mechanism of chronic intestinal failure secondary to SBS is intestinal malabsorption due to the loss of intestinal absorptive surface and more rapid intestinal transit. The successful rehabilitation of a patient with SBS depends upon the management of the three phases of SBS: acute phase, adaptation phase, and maintenance phase.
The acute phase of SBS lasts 3 to 4 weeks and involves metabolic derangement and significant intestinal losses as well as gastric hypersecretion due to the lack of inhibitory hormones that are normally released from the terminal ileum. It requires close monitoring in the hospital setting to avoid sequelae such as dehydration with acute kidney failure, acid-base abnormalities, and electrolyte deficiencies.
The adaptation phase of SBS lasts 1 to 2 years and involves adaptive changes of remaining small bowel to increase the area of bowel available for nutrient absorption, slow down intestinal transit to maximize the time available for absorption, and adaptive hyperphagia. These processes are promoted by the presence of nutrients in the bowel, pancreatic and biliary secretions, and hormones released by the ileum and colon. Chronic intestinal failure – the condition that exists when the adaptation phase fails to occur – is more likely to be reversible in the following situations:
The third and final phase of SBS is the maintenance phase. This phase is managed with special diets, oral or intramuscular supplementation of nutrients, and pharmacological treatments.[1]
Intestinal failure-associated liver disease is a complication of SBS. Histopathological findings include cholestasis, steatosis, steatohepatitis, ductopenia, and perivenular and portal fibrosis.
The primary adverse outcome of SBS is malabsorption secondary to decreased intestinal absorptive surface area and rapid intestinal transit. The most common signs, symptoms, and findings include malnutrition, weight loss, diarrhea, steatorrhea, dehydration, vitamin deficiencies, and electrolyte imbalance. The individual with SBS will likely have undergone extensive small bowel resection related to one of the underlying pathologies listed above.[1]
Initial management of SBS involves maintaining good nutritional status, maximizing the absorptive surface area of the remaining intestine, and preventing complications. This involves early postoperative parenteral nutrition as well as enteral nutrition once the patient's ileus has resolved. This promotes intestinal adaptation which improves absorption of nutrients over time.
Those patients in whom intestinal failure is irreversible will require either lifelong home parenteral nutrition or intestinal transplantation if a life-threatening complication of either SBS or home parenteral nutrition arises. Treatment of SBS, therefore, largely consists of managing and preventing complications that arise as a direct result of SBS or secondarily to home parenteral nutrition. The management of SBS and the prevention of its complications share many of the same treatments.
Surgical management is another important treatment strategy available to patients with SBS. Patients on parenteral nutrition who suffer from rapid transit may benefit from reversing intestinal segments or interposing segments of colon into the small bowel. Those with less than 60 centimeters of small bowel and parenteral nutrition-related complications may be candidates for intestinal transplantation. Patients with dilated bowel secondary to obstruction can sometimes be treated with intestinal tapering or strictureplasty if they have a bowel remnant greater than 120 centimeters or tapering with lengthening if the remnant is less 90 centimeters in adults or less than 30 centimeters in children.[1][3][4]
Those with greater than 180 cm of small bowel generally require no parenteral nutrition. Those with greater than 90 cm will usually require it for less than 1 year. And those with less than 60 cm will likely require lifetime parenteral nutrition.
The primary complications of malabsorption are malnutrition, weight loss, steatorrhea, diarrhea, electrolyte imbalance, and vitamin deficiencies. Other complications include nephrolithiasis due to hyperoxaluria, cholelithiasis, transient gastric hypersecretion, bacterial overgrowth, dehydration, hyponatremia, potassium deficiency, magnesium deficiency, renal failure, calcium oxalate kidney stones, cholestasis secondary to intestinal failure-associated liver disease, gallstones, and d-lactic acidosis.
In adults and older children, steatosis is more common, whereas in infants cholestasis and rapid progression to liver fibrosis is the more common progression. Intestinal failure-associated liver disease deaths are seen in between 16% and 60% of deaths in infants on home parenteral nutrition.[1]
Ultimately, management of SBS requires an interprofessional team led by a physician with gastrointestinal expertise. A gastrointestinal surgeon can provide the appropriate surgical recommendations and management, and a transplant surgeon can expand the patient's therapeutic options. Other essential team members include administrative support, a nurse coordinator to handle the patient's day-to-day management, and a nutritionist. A psychologist and social worker are important to address the psychosocial challenges of SBS.
[1] | Pironi L, Definitions of intestinal failure and the short bowel syndrome. Best practice & research. Clinical gastroenterology. 2016 Apr [PubMed PMID: 27086884] |
[2] | Pironi L,Arends J,Baxter J,Bozzetti F,Peláez RB,Cuerda C,Forbes A,Gabe S,Gillanders L,Holst M,Jeppesen PB,Joly F,Kelly D,Klek S,Irtun Ø,Olde Damink SW,Panisic M,Rasmussen HH,Staun M,Szczepanek K,Van Gossum A,Wanten G,Schneider SM,Shaffer J, ESPEN endorsed recommendations. Definition and classification of intestinal failure in adults. Clinical nutrition (Edinburgh, Scotland). 2015 Apr [PubMed PMID: 25311444] |
[3] | Nightingale J,Woodward JM, Guidelines for management of patients with a short bowel. Gut. 2006 Aug [PubMed PMID: 16837533] |
[4] | Jeppesen PB,Fuglsang KA, Nutritional Therapy in Adult Short Bowel Syndrome Patients with Chronic Intestinal Failure. Gastroenterology clinics of North America. 2018 Mar [PubMed PMID: 29413019] |