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|Dietary Recommendations for Patients with Intestinal Failure|
K.N. Jeejeebhoy, MD, St. Michael’s Hospital, Toronto, Ontario
Intestinal failure occurs when gastrointestinal function is inadequate to maintain the nutrition and hydration of the individual without supplements given via a tube into the upper bowel or via an intravenous catheter.
In order to formulate dietary recommendations based on scientific considerations, it is necessary to understand how intestinal resection alters the physiology of the intestine. The gastrointestinal tract is designed to act as a single unit from the stomach to the colon. Therefore, in order to understand the factors that contribute to intestinal failure, it is necessary to identify the role of each of the components in aiding the digestion and absorption of food and in the maintenance of the fluid and electrolyte status of the host.
The rate of gastric emptying regulates the progress of the meal through the small bowel. In turn, the rate of gastric emptying is dependent upon the consistency of the meal. Gastric emptying of liquids depends upon osmolarity and that of digestible solids on the particle size. Furthermore, intestinal contents entering the distal intestine inhibit gastric emptying.
Small bowel motility is three times slower in the ileum than in the jejunum. In addition, the ileocecal valve may slow transit, especially when part of the ileum has been resected. The normal adult small bowel receives about 5-6 liters of endogenous secretions (digestive juices) and 2-3 liters of exogenous fluids (oral fluids or fluids delivered via a tube) per day. It reabsorbs most of this volume in the small bowel. The amount reabsorbed in the small intestine depends upon the nature of the meal. With a meat and salad meal, most of the fluid is absorbed in the jejunum whereas with a milk and doughnut meal, less is absorbed proximally and more flows distally. In addition, the absorptive processes are different in the jejunum as compared with the ileum. These differences depend partly on the nature of the electrolyte transport processes and partly on the permeability of the intercellular junctions. In general, water absorption is a passive process following the active transport of nutrients and electrolytes. The transport of sodium creates an electrochemical gradient and this drives the uptake of carbohydrates and amino acids across the intestinal mucosa. Additionally, in the ileum there is neutral sodium chloride absorption. However, the net absorption depends not only upon these processes but upon the extent of back diffusion of the transported material back into the intestinal lumen through "leaky” intercellular junctions. In the jejunum these junctions are very leaky and thus jejunal contents are always isotonic (same tonicity as blood) as illustrated in Figure 1. Fluid absorption in this region of the bowel is very inefficient when compared with the ileum. Hence the ileum is important in the conservation of fluid and electrolytes, as shown in Figure 2. It has been estimated that the efficiency of water absorption is 44% and 70% of the ingested load in the jejunum and ileum respectively. For sodium, the corresponding estimates are 13% and 72% (See Table 1).
The colon has the slowest transit varying between 24-150 hours. The intercellular junctions are the tightest in this part of the bowel and the efficiency of water and salt absorption in the colon exceeds 90%5. In addition, carbohydrate is fermented in the colon to short-chain fatty acids (SCFAs), which in turn have two important actions. First, SCFAs enhance salt and water absorption. Second, the energy content of malabsorbed carbohydrates is salvaged by being absorbed as SCFAs. Recent data suggest that in short bowel patients this salvage may be greater than in normals. Thus, the colon becomes an important organ for fluid and electrolyte conservation and for the salvage of may be greater than in normals. Thus, the colon becomes an important organ for fluid and electrolyte conservation and for the salvage of malabsorbed energy substrates in patients with a short bowel.
Unique functions of the ileum
The ileum uniquely absorbs vitamin B12 and bile salts. Bile salts are essential for the efficient absorption of fats and fat-soluble vitamins. Normally the demand for bile salts imposed by fat absorption cannot be met by synthesis alone. The need for bile salts is only met by ileal resorption of bile salts which are then recycled into the intestine about six times per day. With ileal resection, the loss of bile salts increases and is not met by an increase in synthesis. The bile salt pool is depleted and fat absorption is reduced. In addition, loss of bile salts into the colon affects the colonocytes and reduces the ability of the colon to reabsorb salt and water resulting in increased diarrhea. In the colon, bile salts are also dehydroxylated to deoxy bile salts which induce colonic water seControl of diarrheacretion.
EFFECTS OF INTESTINAL RESECTION
Gastric and Intestinal Secretion and Motility
Gastric hypersecretion occurs after small bowel resection in response to increased gastrin output. This hormone may stimulate growth and adaption at the proximal bowel. On the other hand, hypersecretion of acid may reduce nutrient absorption by inactivating pancreatic enzymes. Reducing acid secretion improves absorption in patients with a short bowel. Furthermore, hypersecretion can cause nausea, reflux and hemorrhage from severe esophageal ulceration which may require proton pump inhibitors for control.
Gastric motility is enhanced following small bowel resection. While proximal small bowel resection does not increase the rate of intestinal transit, ileal resection significantly accelerates intestinal transit8,11. In this situation the colon aids in slowing intestinal transit. In patients with a short bowel without a colon, a marker fed by mouth is completely excreted in a few hours.
Absorption of fluid and electrolytes
The effect of intestinal resection depends upon the extent and site of resection. Proximal resection results in no bowel disturbance because the ileum and colon absorb the increased fluid and electrolyte load efficiently. The remaining ileum continues to absorb bile salts and thus there is little reaching the colon to impede salt and water resorption. In contrast, when the ileum is resected, the colon receives a much larger load of fluid and electrolytes and also receives bile salts which reduce its ability to absorb salt and water, resulting in diarrhea. In addition, if the colon is resected, the ability to maintain fluid and electrolyte homeostasis is severely impaired.
Absorption of Nutrients
Absorption of nutrients occurs throughout the small bowel and the removal of the jejunum alone results in the ileum taking over most of the lost function. In this situation there is no malabsorption. In contrast, even a loss of a 100 cm. of ileum causes steatorrhea. The degree of malabsorption increases with the length of resection and the variety of nutrients malabsorbed increases16,17. Balance studies of energy absorption showed that the absorption of fat and carbohydrate were equally reduced to between 50% and 75% of intake. Nitrogen absorption was reduced to a lesser extent, namely to 81% of intake. In patients with a short bowel, Ladefoged et al15 found that the degree of calcium, magnesium, zinc and phosphorus absorption were reduced but did not correlate with the remaining length of bowel and they recommended that in these patients, parenteral supplementation be mandatory. Our studies showed similar reduction in absorption but only half required parenteral replacement. The data taken as a whole suggest that it is easier to meet needs for energy and nitrogen by increasing oral intake than the needs for electrolytes and divalent ions. A review of the literature prior to the availability of parenteral nutrition shows that resections up to 33% result in no malnutrition and those up to 50% could be tolerated without special aids but those in excess of 75% require nutrition support to avoid severe malnutrition.
IMPLICATIONS FOR MANAGEMENT OF SHORT BOWEL SYNDROME
Control of diarrhea
Diarrhea is due to a combination of increased secretions, increased motility and osmotic stimulation of water secretion due to malabsorption of luminal contents. Initially, diarrhea is controlled by keeping the patient NPO to reduce any osmotic component. Gastric hypersecretion can be controlled by the continuous infusion of appropriate doses of intravenous H2 blockers or proton pump inhibitors. In addition, loperamide can be used to slow gastric and intestinal transit. If loperamide does not work, then codeine, phenoxylate or deodorized tincture of opium may be tried.
In the immediate postoperative period all patients will require intravenous fluids and electrolytes to replace losses. Sodium and potassium chloride as well as magnesium are the most important ions to be replaced and plasma levels of these ions should be monitored frequently. Fluid is infused according to measured losses and to maintain an adequate urine output. The infusion is tapered as oral intake and absorption improves.
The next consideration is to determine the best oral diet. In patients who have more than 100 cm of remaining jejunum as the only small bowel remaining, refeeding should be progressive with a view ultimately to feeding a normal oral diet. In patients with less than 100 cm of jejunum, dietary intake and fluids cause increased fluid loss. In patients who have very little small bowel left, the initial target should be small volume isotonic feeds containing a glucose-electrolyte content similar to the oral rehydration solution. The composition of this solution should be glucose 100 mmol/L, sodium chloride 60 mmol/L and sodium citrate 60 mmol/L. It has been shown that fluid absorption improves as sodium concentration increases. To provide sufficient sodium to absorb dietary carbohydrate, it is necessary to ingest 10-15 g of sodium chloride as tablets daily with meals. Such a regimen avoids osmotic stimulation of secretion, yet stimulates the bowel to absorb, thus promoting adaptation. Progressive feeding should be attempted with the following plan. The same carbohydrate- electrolyte feeds as above should be started. This high-salt intake has been shown to be well absorbed by patients with massive resection who have previously been dependent on intravenous fluids. The diet should be lactose- free since lactase levels in short bowel patients are reduced. Vitamin B12 absorption should be measured and if subnormal injections of 250 micrograms per month should be started.
Early observations suggested that low-fat diets are beneficial. The theory behind this concept was that malabsorbed long-chain triglycerides (LCT) cause colonic water secretion. However, soluble carbohydrates are also malabsorbed in short bowel syndrome. Using a controlled crossover design in two studies12,18, we showed that a high-fat diet was comparable to a high-carbohydrate diet in regard to total fluid, energy, nitrogen, sodium, potassium and divalent ion absorption. We therefore recommend a low-lactose diet containing high calories from both fat and carbohydrate and a high nitrogen intake. In adults who require about 30 kcals/kg/day, we aim to increase intake gradually to about 60 kcals/kg/day to provide sufficient absorbed calories despite malabsorption. The rationale for this approach is discussed by Woolf et al12. Supplements of potassium, magnesium and zinc are given while monitoring serum levels. In particular, potassium as gluconate may be added at a concentration of 12 mmol/L in the carbohydrate-electrolyte fluid. In addition, we have found that magnesium heptogluconate is especially useful as a supplement to correct hypomagnesemia without causing diarrhea. It is possible to add 30 mmol of magnesium per liter of glucose-electrolyte mixture and sipped over the day.
In patients with less than 100 cm of remaining jejunum and in those with a combined small bowel and colon resection, parenteral nutrition is lifesaving. It is started in such patients within a few days of the resection and initially 32 kcals/kg of a mixed energy substrate and 1 g/kg amino acids is infused with sodium 150-200 mM, potassium 60-100 mM, calcium 9-11 mM, magnesium 7-15 mM and zinc 70-100 micromoles per day. Among trace elements, zinc is the most important as we have found large losses in patients with a high endogenous output of intestinal fluids. Oral feeds are simultaneously started and attempts are made to reduce parenteral feeding as oral feeds are increased. It will become apparent whether the patients need parenteral feeding on a long-term basis. In this case, the patient should be started on a program of home parenteral nutrition (HPN). We have found that as the bowel adapts over months and even years, the patient requires less parenteral feeding and ultimately about 30% of our patients initially requiring HPN can be weaned off HPN by using up to 2 liters of oral rehydration solution, high calorie diet and supplements of potassium, magnesium, calcium, fat-soluble vitamins and zinc. They are monitored regularly until the weight is stable and they are in electrolyte balance. Hypomagnesemia is a particularly serious problem in these patients. Ingestion of magnesium salts orally enhances diarrhea and it often becomes difficult to use magnesium supplements orally. The author has successfully used Magnesium heptogluconate for this purpose. This preparation is available as a palatable liquid which is added to the gastrolyte supplement in quantities of 30 mM per day. If this approach is not successful, then magnesium sulfate is infused through an indwelling catheter in doses of 12 mM one to three times a week to supplement the oral intake. Normally, specific supplementation with Vitamin K is not necessary for patients not on Parenteral Nutrition. The prothrombin time (INR) is monitored with clinic visits and if raised then supplementation is necessary. However, in the author’s experience it was necessary in only one patient over the years.
Vitamin supplementation needs comment. These patients can absorb water-soluble vitamins but have difficulty absorbing fat-soluble vitamins. They require large doses of vitamin A, D and E to maintain normal levels. Also pills often pass out whole in these patients, hence liquid preparations have to be used. The author recommends the measurement of these vitamin levels and supplementation with aqueous preparations of vitamin A and E (Aqasol A and E) and 1,25 dihydroxy-vitamin D in doses which normalize the plasma levels. Normalization may not be possible with oral vitamins in some individuals, especially vitamin E levels.
In some patients an oral diet will maintain weight and body composition but intravenous fluids and electrolytes are needed to maintain hydration and normal levels of electrolytes, especially magnesium. Patients with a very short bowel may not be able to maintain normal weight and body composition with only intravenous fluids and electrolytes for hydration. These patients need full parenteral nutrition containing protein, energy, electrolytes, vitamins and trace elements.
Jejunal resection with intact ileum and colon
Patients in this category can be fed orally immediately and rarely have any problems. The conventional approach is to give clear fluids, then a liquid diet with nutrients followed by a soft and then regular diet. There is no evidence this graduated approach is beneficial. Patients can often take fluids and solids in small quantities as soon as they can pass gas and feel hungry. The process of refeeding after resection is given in detail in the next section.
Ileal resection of less than 100 cm with colon largely intact
Patients in this category have so-called bile salt-induced diarrhea and are best helped by the administration of 4 g of cholestyramine three times a day to bind bile salts left unabsorbed by the resected ileum. Vitamin B12 absorption should be measured and if low B12 (to be consistent) should be injected intramuscularly in doses of 250 ug per month.
Ileal resection of more than 100 to 200 cm with colon largely intact:
This group of patients has little difficulty in maintaining nutrition with an oral diet but has fatty acid diarrhea. For such a patient, fat restriction is mandatory. With the larger resection, the bile salt pool is depleted and cholestyramine is contraindicated because it binds and further decreases bile salts. Parenteral vitamin B12 replacement is required.
Resection in excess of 200 cm of ileum or lesser resection with associated colectomy:
Patients of this class require the graduated parenteral adaptation program indicated previously.
Resection leaving less than 60 cm small bowel or only duodenum - Massive bowel resection:
Patients in this category need HPN indefinitely. However, many patients even in this category may show a surprising degree of adaptation and require less parenteral nutrition over time. The indication to reduce parenteral nutrition is weight gain beyond the desired limit and the fact that reduced infusion does not cause electrolyte imbalance and dehydration.
of the function of the different segments of the gastrointestinal tract in
promoting absorption and motility helps clarify the effects of intestinal
resection and disease. On the basis of this information, a rational plan of
management can be formulated to maximize absorption of nutrients including fluid
and electrolytes, and to understand the need for supplements as given in the
accompanying algorithm (see figure).
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