The Evolving Medical Management of Short Bowel Syndrome

Abstract

management. Physiology of short bowel syndrome Patients with SBS undergo significant metabolic alterations due to the anatomical loss of the small bowel. Malabsorption of nutrients arises due to reduction of the intestinal absorptive area, resulting in nutritional depletion of vital nutrients, weight loss, diarrhea and dehydration. Transient hypergastrinemia may occur, due to loss of the enteric hormonal feedback (protein PYY, glucagon-like peptide-1 (GLP-1), Cholecystokinin (CCK) and secretin) that helps to reduce gastric secretion. Altered motility is seen due to the loss of the ‘ileal brake” that normally would serve to slow transit of nutrients, with reduction of the hormones glucagon-like peptide-2 (GLP-2), peptide YY, GLP-1, and neurotensin. Patients with significant distal ileal resection, >100 cm, are at risk for vitamin B12 deficiency, bile salt diarrhea and development of gallstones. This is due to the loss of the ileal area where vitamin B12 is absorbed and where bile salts are recycled back to the liver via enterohepatic circulation. This will result in increased stool output as bile salts enter the colon, and exert a cathartic action. Oxalate kidney stones may develop due to excessive absorption of oxalate in the colon. Bacterial overgrowth may arise as well. There is also a risk of D-lactic acidosis due to the colonic bacterial fermentation of simple Carbohydrates (CHO). Nutritional management of SBS Intestinal Rehabilitation is an important concept in the management of these complex patients with the aim of facilitating nutrient and fluid absorption and reduction of the need for parenteral support, in order to achieve the best possible quality of life. Nutritional management of SBS includes various interventions, which includes the use of enteral nutrition, therapeutic manipulation of the diet and parenteral nutrition when required. Nutritional interventions for oral intake are individualized and designed to stimulate intestinal adaptation to maximize the function of existing small bowel. The gut has the ability to adapt over the course of 1 to 2 years, (intestinal adaptation), which includes the hypertrophy of the villi leading to a greater absorptive area to optimize nutritional capacity. The known length of the remaining small bowel and whether a colon is present or not determines the nutritional therapies utilized. Enteral nutrition is the favored route. The use of gastrostomy or jejunostomy tubes to facilitate nocturnal feeding should also be considered. Parenteral nutrition (PN), along with intravenous fluids may be required initially until the patient stabilizes. Trophic enteral feeds can be used in conjunction of PN initially and with enteral feed advancement, can help to transition the SBS patient off PN. The use of an isotonic polymeric enteral formula is initially preferred to stimulate intestinal adaptation. If a patient does not adequately tolerate a polymeric enteral formula, then an isotonic elemental enteral formula can be attempted. A variety of polymeric and elemental enteral formulas are available. Patients with 100 cm small bowel or less without a colon or left with 50 cm small bowel with a colon inevitably stay TPN dependent. These patients are referred to as SBS-Intestinal Failure (IF) patients. Parenteral nutrition, however, carries a significant risk of line sepsis, vascular occlusion and liver dysfunction. Reduction and potential weaning of PN is the goal, and is done gradually and is initiated with a modest reduction in caloric provision. The weaning process is individualized, and is dependent on how well the patient progresses with increasing oral intake and/or enteral feeds while stabilizing nutritional parameters, such as weight status, hydration and stool output. The macronutrient composition of the diet will differ between SBS patients that have a colon and those that do not and have end jejunostomies or ileostomies. Overall, a high caloric intake is needed to compensate for the malabsorption of nutrients that may occur initially with SBS.