Many patients with a surprisingly short segment of small intestine eventually develop the ability to live without parenteral nutrition as a result of a compensatory increase in mucosal surface area caused by the adaptive response to massive resection. This compensatory growth is dominated by villus hyperplasia, although some dilatation and lengthening of the remaining small intestine does occur.

As might be expected, increases in villus length and in the number of enterocytes available for absorption per centimeter of bowel are accompanied by a gradual increase in the absorption of nearly all nutrients.

Stimulation of the adaptation process becomes the primary goal of therapy in the treatment of patients with short bowel syndrome. The importance of intraluminal nutrition in stimulating this process has been well documented. The intraluminal nutrients not only are necessary to produce adaptation, but also are essential to maintain the structural and functional integrity of the small intestine.

Nutrients appear to stimulate mucosal adaptation through three independent, but possibly related, mechanisms:

During phase I, achieving nutritional repletion and stabilizing fluid and electrolyte balance are the major goals of therapy. Home therapy also should be contemplated at this time and, if it is at all possible, organization of and instruction regarding home TPN should be initiated early.

Once it is apparent that the child will require long-term parenteral nutrition venous access with an indwelling catheter or infusion part is required. The decision as to whether TPN will be necessary may be obvious in the case of massive small bowel resection. In questionable patients, failure of adequate growth on a trial of total enteral nutrition is required to make the decision. Parenteral nutrition usually is begun using a 10% dextrose and 2.5% crystalline amino acid solution infused at a rate approximately equal to 1.3 times the maintenance fluid rate for the patient. Incremental increases in dextrose concentration then follow, up to 15% and 20% each day, to allow the patient to achieve total caloric requirements parenterally by the third day. Maintenance quantities of parenteral vitamins and trace metals are added to the parenteral nutrition solution, usually through the use of commercial preparations. In patients with high-output proximal fistulas, additional zinc supplementation may be required. Extra zinc also should be considered in small, preterm infants. Twenty-percent intravenous lipid solution should be administered a minimum of twice weekly to provide at least 8% of the total caloric intake as fat, if substantial enteral feedings are not administered concurrently. Although the primary purpose of intravenous lipid is to prevent the deficiency of essential fatty acids, daily use of the lipid solution may allow additional calories to be provided, if they are needed.

With few exceptions, standard pediatric electrolyte concentrations can be administered with little variation. Routinely, 30 mEq of sodium chloride, 20 mEq of potassium phosphate, 10 mEq of calcium gluconate, and 5 mEq of magnesium sulfate can be added to each liter of TPN solution. Depending on the amino acid solution used, some sodium may need to be administered in the form of acetate to buffer the solution. This will be readily apparent if the patient becomes acidotic while receiving parenteral nutrition. Providing enough calcium phosphate is a problem in some small infants. The addition of L-cysteine, 1,000 mg/L, may allow the provision of additional calcium and phosphorus in the solution without precipitation.

Appropriate monitoring and the replacement of abnormal losses is the key to the use of standard solutions in patients with short bowel syndrome. Patients receiving long-term parenteral nutrition can be managed with infrequent changes in the composition of TPN, provided that abnormal losses are replaced. For example, if a patient has a jejunal fistula or high-volume stool losses, electrolyte concentrations can be measured in the fistula fluid or the stool, and a comparable mixture of fluid and electrolytes can be replaced on a volume-per-volume basis. This prevents excessive loss of fluid and electrolytes, and the patient then can be maintained on standard TPN solutions for prolonged periods. The additional cost of the second infusion pump is more than offset by minimized wastage of parenteral nutrition solution as well as by the relative stability of the patient, which results in a need for fewer serum electrolyte determinations.

During early phases of therapy, electrolyte, blood urea nitrogen (BUN), and glucose levels should be measured daily. After a short period, however, these determinations can be made less frequently. In patients receiving long-term therapy, monitoring is required as infrequently as every 1 to 3 months, once appropriate needs are established. Periodic determination of calcium, magnesium, phosphorus, liver enzymes and, occasionally, trace element and vitamin levels is required.