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Therapeutics/Short Bowel Syndrome


Case

A 57-year-old man with atrial fibrillation develops severe abdominal pain. He is diagnosed with an acute abdomen. He undergoes an emergent exploratory laparotomy, where an embolism is found in the superior mesenteric artery, and 200cm of gangrenous small bowel is resected, and an ileostomy is created. Two days later, the patient undergoes a second-look surgery, and a jejunocolic anastamosis is created. total parenteral nutrition is initiated postoperatively, and, once bowel function returns, enteral nutrition is initiated with a goal of gradually decreasing the requirement for total parenteral nutrition.

Therapeutics

Most available data on the treatment of Short bowel syndrome are based on retrospective analyses of case series, and are detailed below.

Medical Management

The most important aspects in the management of patients with Short bowel syndrome are to provide adequate nutrition, to provide sufficient fluid and electrolytes to prevent dehydration, and to correct and prevent acid-base disturbances. Furthermore, it is important to treat the underlying disorder, whenever possible, such as Crohn disease.

Table Causes of short bowel syndrome and intestinal failure

Adults
Catastrophic vascular accidents
Superior mesenteric venous thrombosis
Superior mesenteric arterial embolism
Superior mesenteric arterial thrombosis
Chronic intestinal pseudo-obstruction*
Intestinal resection for tumor
Midgut volvulus
Multiple intestinal resections for Crohn disease
Radiation enteritis*
Refractory sprue*
Scleroderma and mixed connective tissue disease*
Trauma
Children
Congenital villous atrophy*
Extensive aganglionosis*
Gastroschisis
Jejunal or ileal atresia
Necrotizing enterocolitis
Microvillus inclusion disease*
Midgut volvulus

Medication absorption is often impaired in these patients, as absorption is a function of both intestinal surface area and contact time. The oral or enteral route for medications should be used whenever possible, in order to minimize total parenteral nutrition catheter manipulations. However, many medications are absorbed in the jejunum, and thus, in the absence of decreased intestinal transit time, absorption will be minimally impacted.

Massive enterectomy is associated with gastric hyper-secretion for the initial 6 months, and these patients will benefit from acid reduction, which serves to reduce fluid losses. High doses of oral H2-recep-tor antagonists or proton pump inhibitors, or intravenous preparations, are typically necessary due to medication malabsorption.

In addition, excessive fluid losses typically require the use of antimotility agents, such as high doses of loperamide hydrochloride (4-16 mg/day) or diphenoxylate. If these agents are ineffective, codeine sulfate or tincture of opium are often necessary. Rarely, patients may require treatment with octreotide, which may be useful by slowing intestinal transit and increasing water and sodium absorption (Table Therapeutic agents used to decrease intestinal transit and stool volume).

Oral rehydration solutions improve hydration and decrease total parenteral nutrition fluid requirements, especially in those patients with a proximal jejunostomy, or in those with less than 100cm of jejunum remaining. These solutions take advantage of the sodium-glucose cotransporter and the solvent drag that follows intracellular transport of sodium and water. Optimal solutions have a sodium concentration of at least 90mEq/L. The best and least expensive Oral rehydration solutions is that recommended by the World Health Organization (WHO), with substantially more sodium than most commercially available solutions. Patients with Short bowel syndrome should be advised to avoid consumption of water and to drink Oral rehydration solutions whenever thirsty.

Table Therapeutic agents used to decrease intestinal transit and stool volume

Agent Dosage
Loperamide 4-6mg four times daily
Diphenoxylate/atropine 2.5-5mg four times daily
Codeine sulfate 15 mg two to four times daily
Ranitidine 300 mg twice daily
Omeprazole 40mg twice daily
Octreotide 50-100 ng SC twice daily

Patients who have undergone massive enterectomy typically require total parenteral nutrition initially. Once the patient is hemo-dynamically stable, enteral nutrition should be started as soon as possible, and advanced gradually as tolerated. Once patients are able to eat, they should be encouraged to eat a regular diet, as modified below, and to eat substantially more than what was typical before the resection (hyperphagia), to compensate for the malabsorption. This may be accomplished by the use of multiple small meals, and is perhaps the single most important dietary intervention to reduce the need for total parenteral nutrition.

The absorption of nitrogenous macronutrients is least affected by the decreased intestinal absorptive surfaced area. It has been reasoned that if dietary protein were provided in a predigested form, it would be more readily absorbed. However, in seven patients with an end-jejunostomy, energy, carbohydrate, nitrogen, fat, electrolyte, fluid, and mineral absorption, as well as stool weight, were similar regardless of whether a peptide-based enteral formula was provided. Based on this experience, the utility of peptide-based diets is largely without merit.

Most intestinal dissacharidases are present in highest concentration in the proximal small intestine, which often remains intact in patients who undergo massive enterectomy. In the absence of significant jejunal resection or documented lactase deficiency, lactose-containing foods should not be limited, as they are an important source of dietary calcium.

Patients with Short bowel syndrome whose colon is in continuity should consume a high-complex-carbohydrate diet, as starches, non-starch polysaccharides, and soluble fiber pass undigested into the colon, where bacteria ferment them into short-chain fatty acids, including butyrate, pro-prionate, and acetate. Short-chain fatty acids provide fuel for the colonocyte and significantly reduce fecal energy losses. As such, the colon becomes an important digestive organ in patients with Short bowel syndrome. Furthermore, sodium and water absorption are stimulated by short-chain fatty acids, although decreased fecal losses have not been documented clinically.

Lipid digestion may be impaired, as micelle formation is limited due to ileal bile salt malabsorption. Treatment with bile salt replacement, such as ox bile or the conjugated bile acid chylosarcosine, has been reported in a few patients, decreasing fecal fat in most, but leaving fecal volume unchanged or increased. Cholestyramine may be useful in decreasing bile-salt-induced diarrhea in those with less than 100 cm of terminal ileum resected, but should not be used in patients with more than 100 cm of ileal resection, because it can worsen steatorrhea by binding dietary lipid.

In those patients with their colon in continuity, a high-fat diet can lead to more diarrhea. However, this must be balanced against the fact that fat is an important energy source, given its increased energy density when compared to carbohydrates. Overall, limited data are available to support the use of low-fat diets.

It is important to assess the vitamin and mineral status of these patients at regular intervals. It is unusual to develop water-soluble vitamin deficiencies, except in those with duodenostomies or proximal jejunostomies, because they are absorbed in the proximal jejunum. However, Mate deficiency may develop in patients with proximal jejunal resection, and these patients should receive daily folate. In addition, vitamin B12 deficiency is seen in patients who have greater than 60 cm of terminal ileum resected, and supplementation is necessary.

Fat soluble vitamin deficiencies are more common, and develop because of decreased bile salt reabsorption and associated fat maldigestion. Cholestyramine can cause fat-soluble vitamin deficiency as well, due to its effects of binding to bile salts, and should not be used if more than 100 cm of terminal ileum has been resected, as it will lead to enhanced malabsorption. Vitamin A deficiency is characterized by night blindness and xerophthalmia. Vitamin D deficiency manifests as osteomalacia. Vitamin E deficiency manifests as hemoly-sis and various neurologic deficits. Vitamin K deficiency is uncommon in those patients with an intact colon, as 60% of vitamin K is synthesized by colonic bacteria; however, vitamin K deficiency can be seen in those without a residual colon or in those who have taken antibiotics.

Fecal losses of zinc and selenium can be significant, and deficiencies will develop. Zinc deficiency has been associated with growth abnormalities, delayed wound healing, and immune dysfunction. Selenium deficiency has been associated with various abnormalities, including cardiomyopathy, peripheral neuropathy, and proximal muscle weakness and pain.

The length of remaining bowel necessary to prevent dependence on total parenteral nutrition is approximately 100 cm in the absence of an intact colon, or 60 cm in the presence of a colon. For those who require long-term total parenteral nutrition, gradual attempts should be made to wean the patients from parenteral nutrition, and approximately 50% can discontinue total parenteral nutrition and resume oral intake after 1-2 years. Because total parenteral nutrition solutions are hypertonic, they are infused into a central vein. Total parenteral nutrition is typically given in a continuous fashion in the initial postoperative phase, but over time the infusions are gradually compressed into to a cycled regimen (with adjustments to volume and nutritional support).

Growth factors have been studied in patients with Short bowel syndrome. A double-blinded, randomized, placebo controlled trial of growth hormone in 41 total parenteral nutrition-dependent patients, showed that total parenteral nutrition requirements in treated patients could be reduced by an additional 2 L/week over the reduction with standard therapies. In addition, treatment with a synthetic analogue of glucagon-like peptide 2 (GLP 2), an intestinotrophic agent, has been shown to increase villous height, with increased fluid absorption, as well as modest improvements in energy absorption. However, these effects regressed once the medication was discontinued.

Surgical Management

Anastamosis of the small bowel to the colon is the most important surgical procedure, enhancing the ability of the colon to become an energy-absorptive organ, and allowing for decreased dependence on total parenteral nutrition. Other surgical procedures to taper dilated, non-functional intestine are available, but should be reserved for highly selected individuals with dilated, non-functional segments of intestine. In the Bianchi procedure, the surgeon divides the dilated bowel and performs an end-to-end anastamosis, thereby doubling the bowel length. In the serial transverse enteroplasty procedure, a linear staple is applied from alternating and opposite directions along the mesenteric border to incompletely divide the dilated intestine, which leads to tapering of the dilated intestine.

The main indication for intestinal transplantation is total parenteral nutrition-dependent Short bowel syndrome complicated by progressive liver disease, and as such, intestinal transplantation is often combined with liver transplantation. If patients are referred for evaluation for transplantation prior to the development of advanced fibrosis, isolated intestinal transplantation can be done. These patients have a better prognosis than those requiring a combined transplant. In addition, patients with significant fluid losses and refractory dehydration, despite appropriate medical management, are candidates for intestinal transplantation. Survival has improved considerably since intestinal transplantation was introduced, and patients who have undergone transplantation more recently have better survival, largely due to improved surgical techniques and improved immunosuppressive regimens. And while the short-term survival in those receiving intestinal transplantation approaches 90%, the 5-year survival is closer to 50%, which is far worse than those requiring long-term home total parenteral nutrition. As such, intestinal transplantation is not a replacement for total parenteral nutrition. Along those lines, both premature intestinal transplantation, and late referral for transplantation, which often requires the addition of a liver graft, must be avoided. High-risk patients should be identified early and referred to a center where intestinal rehabilitation and transplantation are both practiced.

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