Short Bowel Syndrome

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Chapter 70 Short Bowel Syndrome

PATHOPHYSIOLOGY

Short bowel syndrome (SBS) is the syndrome of malabsorption and malnutrition that occurs because of a congenitally malfunctioning bowel or after resection of small bowel necessitated by congenital or acquired conditions (Box 70-1). Symptoms of SBS include chronic diarrhea, impaired nutrient absorption, malnutrition, and poor growth and development. In addition, many affected children are chronically dependent on parenteral nutrition (PN), which can lead to liver dysfunction and disease.

SBS has three characteristic stages. Stage I begins in the immediate postoperative period and usually lasts for 7 to 10 days after the enterostomy is created. Characteristics of this stage include intractable diarrhea with massive water, fluid and electrolyte losses, dependence on parenteral nutrition and, possibly, bowel mucosa atrophy. Stage II begins 2 weeks later and can last up to 1 year after surgery. During stage II, gastric acid hypersecretion can lead to quick intestinal transit time and diarrhea, impaired pancreatic enzyme function, and gastric ulcers. At the end of stage II, stabilization of diarrhea and progression of enteral feedings occur. These changes signal an adaptive hyperplasia of the intestinal mucosa including elongation of both intestinal villi and crypts. Stage III is seen up to 2 years after the surgery. This stage represents control of diarrhea and increased tolerance of enteral nutrition (EN). Oftentimes stomas are reanastomosed at this time. Reaching this stage is dependent upon bowel adaptation, which is critical to the patient with SBS. Bowel adaptation is, in turn, dependent upon many factors, the first of which is intestinal length. Most surgeons agree the 25 cm of small bowel without an intact ileocecal valve (ICV), or 15 cm of small bowel with an intact ICV, is necessary for tolerance of enteral feedings. The second significant factor is the presence of the ICV. The ICV slows intestinal transit time, allowing increased nutrient and fluid absorption, and prevents contamination of the small bowel with colonic flora. Although important, the presence of the ICV is not absolutely necessary, depending on bowel length. The third factor important to bowel adaptation is the location of resection. The adaptive response is greater in the ileum than in the jejunum. Changes in the crypts and the villi allow the ileum to take over some of the functions of the jejunum, whereas the reverse is not true.

The fourth factor in bowel adaptation is the reintroduction of EN. Early and aggressive initiation and advancement of EN, especially human breast milk, protein hydrolysate formulas, or amino acid–containing formulas, appears to promote intestinal adaptation. The fifth factor is the age of the infant at resection. Because intestinal length doubles between the second trimester and full term, a preterm infant has a great capacity for adaptation. The final factor is individual response. Liver tolerance of chronic PN, the number and virulence of infections, and the development of bowel obstructions from strictures or adhesions all seem to play an important role in the overall outcome of patients with SBS.