Dietary Recommendations for Patients with Intestinal Failure
By
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.
PHYSIOLOGICAL CONSIDERATIONS
Stomach
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
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).
Table 1
Colon
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
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 secretion.
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.
Intravenous fluids
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.
Oral Feeding
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.
Parenteral Nutrition
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.
Summary:
Appreciation
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).
