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CHAPTER 71

Short Bowel Syndrome

Alice Mears
Kokila Lakhoo
Alastair J. W. Millar

Introduction slowest transit time, between 24 and 150 hours. The efficiency of salt
Short bowel syndrome (SBS) is defined as intestinal failure due to a and water absorption also varies in the different parts of the intestine.
loss of intestine resulting in inadequate length of bowel for maintaining The jejunum is very inefficient, with an efficiency of water absorption of
the nutrition and hydration of the individual without either intravenous 44% compared to 70% in the ileum and greater than 90% in the colon.
or oral supplementation. The corresponding estimates for efficiency of salt absorption are 13%
With some reported exceptions, the minimum length of small bowel in the jejunum, 72% in the ileum, and greater than 90% in the colon.
required for infant survival on enteral feeds is generally 25 cm in the Jejunum
presence of an intact ileocaecal valve (ICV) and colon, and 40 cm If the jejunum alone is lost, there is no permanent defect in absorp-
without an ICV and large bowel. Note that norms of intestinal length vary tion—the ileum will take over. However, the jejunum normally releases
considerably, with a range of 250 cm to 300 cm of small bowel at term. the hormones cholecystokinin, serotonin, gastric inhibitory peptide,
The estimated length in a preterm infant of 26 and 32 weeks gestation and secretin. Lower secretion of these hormones due to absence of the
is 70 cm and 120 cm, respectively. Thus, gestational age is an important jejunum will result in decreased pancreatic secretion, gallbladder con-
factor. However, an infant is considered to have SBS when he or she traction, and gastric hypersecretion.
behaves as if SBS is present, and the infant should be treated as such. Ileum
The intestine has the ability to adapt over time such that up to half The ileum is unique in absorbing vitamin B and bile salts. Absorption
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of patients with SBS who initially require total parenteral nutrition of nutrients takes place throughout the small bowel. Ileal resection
(TPN) may be weaned off and gradually gain independence from results in decreased transit times and salt and water absorption. A larger
TPN. However, in the absence of the availability of TPN, SBS carries than normal volume of fluid and electrolytes enters the colon. The reab-
a dismal prognosis. The management of SBS is resource-intense, sorption of bile salts is decreased and so their synthesis is increased.
requiring the availability of intensive care, TPN, and expert medical The flow of unabsorbed bile salts into the colon irritates the colon and
and surgical intervention. Even in optimal settings, infants and children impairs its ability to absorb salt and water, leading to choleretic diar-
with SBS suffer extensive morbidity and mortality. In most countries in rhoea. The depletion of the bile salt pool leads to cholelithiasis and fat
Africa where TPN is not available, the outcomes are poor.
malabsorption, resulting in steatorrhoea.
Demographics The degree of fat and carbohydrate malabsorption is related to the
Short bowel syndrome is mercifully rare. In Europe, the incidence is length of ileum resected. There is also reduced absorption of essential
1
estimated to be approximately 2 per million. According to Gupta et al., minerals, including calcium, magnesium, zinc, and phosphorus.
the incidence of SBS in neonates is around 3 per 100,000 births per year. Furthermore, there is an excessive loss of zinc in diarrhoea, leading to
In Africa, the incidence is unknown because survival is close to zero. immune deficiency.
Aetiology Ileocaecal Valve
Some of the common causes of short bowel syndrome are shown in Table Loss of the ICV reduces gut transit time. The loss of this barrier
71.1. SBS can be congenital, but is more generally acquired from surgi- between the small and large bowel also leads to bacterial overgrowth
cal resection of bowel. Of the congenital bowel atresias type 3b (“apple of the remaining gut.
peel” type) and type 4 (multiple atresias, “string of sausages” type) are Colon
most likely to result in SBS. Functional SBS can also occur where there It is thought that the colon in SBS is important for driving adaptation
is severe malabsorption despite adequate bowel length or intact bowel. of the gut as well as assuming an increased importance in absorption
of water, potassium, and sodium as well as carbohydrates. Without the
Table 71.1: Common causes of short bowel syndrome.
colon and ICV a longer length of ileum is required for survival.
Congenital Acquired Intestinal Adaptation
Atresia Midgut volvulus 2
Gastroschisis Mesenteric infarction (e.g., sickle cell crisis) Intestinal adaptation is the process whereby the intestine adjusts to its
Hirschsprungs disease Necrotising enterocolitis; adhesive band loss of length through hyperplasia of the mucosal surface in an effort
(long segment) obstruction/strangulation to increase its absorptive capacity. The bowel dilates, lengthens, and
Trauma
thickens to increase the efficiency of absorption per unit length. There
is an increase in the number of cells in the proliferating zones of the
Pathophysiology crypts, and villus height increases, resulting in an increased surface area
for absorption. Histological evidence of adaptation can be seen from
The effects of loss of bowel length depend on the type and length of 48 hours after bowel resection, and diarrhoea is seen to decrease over
bowel remaining. 1
the first 3 months. Early adaptation may take years and is greater with
Small bowel motility is three times slower in the ileum than in the
proximal than distal bowel resection.
jejunum. The ileo-caecal valve also slows transit. The colon has the