Short Bowel Syndrome: Epidemiology, Pathophysiology, and Adaptation

Short bowel syndrome (SBS) is a relatively common, often lethal, and highly costly medical problem in North America. Necrotizing enterocolitis (NEC) is the leading cause of SBS in the United States. An important fact to remember is that the length of the small bowel in a 28-week preterm infant is about 150 cm and in a term infant is about 250 cm. Twenty percent of this length is generally sufficient to allow dependence on parenteral nutrition (PN) via intestinal adaptation. This process is driven by significant increases in circulating trophic hormones, such as cholecystokinin, epidermal and keratinocyte growth factors, growth hormone, insulin-like growth factor-1, and glucagon-like peptide-2. These hormones produce hypertrophy and hyperplasia of the villi, along with increases in specific brush border membrane absorption mechanisms, such as glucose-sodium cotransport (via SGLT-1) and peptide transport (via Pep-T1). Currently, the best clinical markers of intestinal adaptation are the calculated percentage of enteral versus parenteral calories in a growing infant who has SBS and the serum concentrations of citrulline, an amino acid synthesized by mature enterocytes that has been used as a measure of functional intestinal mass.