Weaning of parenteral nutrition

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The relatively recent concept of intestinal rehabilitation emphasizes strategies to reduce or eliminate the need for PN and intestinal transplantation and can be applied both to adult and pediatric populations [102] (Fig. 8.1). A major component of intestinal rehabilitation consists of medication, dietary and fluid manipulation. Major lifestyle changes and increased out-of-pocket expenses are required on the part of the patient. In addition, the 'trade-off' to the patient for not being on PN is the need to take several medications orally and increase the amount of food and fluid ingested daily. Patient education relative to the underlying disease process and the treatments being prescribed is important to enhance compliance with the care plan.

Table 8.6 lists a number of clinical factors considered useful in predicting the success of eliminating the use of PN in SBS patients [5]. Regardless of the bowel anatomy, an aggressive attempt to wean PN should be undertaken in all SBS patients. Recently, Crenn and colleagues evaluated plasma citrulline, a non-protein amino acid

Attempt To Wean PN

Optimize diet and fluids Aggressive use of antisecretory and antimot ility agents Restore bowel continuity if possible

Careful monitoring of status Micronutrient supplementation

Successful

Unsuccessful or incomplete

Use of r-hGH or participation in investigational studies using other trophic factors

Appropriate nontransplant surgery candidate

Unable to to lerate home PN

Tolerating home PN

Isolated intestine or combined intestine/liver transplant

Continue to monitor for complications

Successful

Unsuccessful or incomplete

Fig. 8.1. Suggested approach to wean parenteral nutrition. Modified from [102] with permission from Blackwell Publishing. PN parenteral nutrition; r-hGH recombinant human growth hormone.

Table 8.6

Clinical factors predictive of successful weaning from parenteral nutrition

Length of the remaining bowel

Presence of a colon

Presence of an ileum/ileocecal valve

Absence of residual mucosal disease in the bowel

Degree to which intestinal adaptation has occurred

Patient age

Duration of time on parenteral nutrition

Nutritional status prior to attempted weaning parenteral nutrition

Fasting plasma citrulline level (?)

Use of recombinant human growth hormone (?)

produced by the intestinal mucosa, as a potential biological marker of either permanent or transient intestinal failure. A level <20 ^mol/l classified SBS patients with permanent intestinal failure with high positive and negative predictive values, and was a more reliable indicator than anatomic variables to distinguish transient from permanent intestinal failure [103]. Nevertheless, successful elimination of PN long-term has been demonstrated in several patients with fasting plasma citrulline levels <20 ^mol/l using techniques discussed in this review [104].

A critical component of PN weaning is to have goals in mind when deciding the frequency and amount of PN to wean [105]. Importantly, diet, fluid intake and medications should be optimized before PN weaning begins. It should be established from the outset whether the realistic goal is to reduce PN requirements or to completely eliminate PN based on factors discussed previously. In addition, certain criteria should be met before reducing PN. In general, meeting the daily calorie and fluid intake goals established for the patient with careful and frequent follow-up and subsequent reductions in PN based on tolerance as determined by the development of symptoms, stool and urine output, electrolyte and micronutrient levels, weight and hydration status is sufficient. With regards to monitoring hydration status, one approach that may be useful is to maintain the urinary sodium concentration >20 mEq/l and daily urinary volume > 11. Although an optimal interval for making PN reduction decisions has not been defined, once/week would seem appropriate while acknowledging that this needs to be individualized. PN reductions can be made by either decreasing the days that PN is infused/week or by decreasing the daily PN infusion volume equally throughout the week.

Micronutrient supplementation becomes necessary as PN is weaned and levels require periodic monitoring. The frequency of monitoring will depend upon the stage of PN weaning and the presence of existing or prior deficiencies [105]. Table 8.7 provides examples of vitamin and mineral supplementation for SBS patients. Because water-soluble vitamins are absorbed in the proximal small bowel, deficiencies in SBS patients are uncommon. In contrast, fat-soluble vitamin and essential fatty acid deficiencies are more commonly encountered. Supplemental zinc, and occasionally selenium, may be required in the presence excessive stool losses. Iron supplementation is infrequently needed as it is absorbed in the upper gastrointestinal tract, an uncommon site of resection in SBS patients. Lifetime administration of supplemental vitamin B12, usually administered subcutaneously on a monthly basis, is needed in those with more than 50 to 60 cm of terminal ileum removed [106].

Hypomagnesemia occurs commonly as a result of secondary hyper-aldosteronism, which generally results from the loss of magnesium-absorbing gut, the binding of magnesium by unabsorbed fatty acids and sodium/water depletion that increases urinary magnesium losses. This can become a difficult problem to correct non-parenterally [1]. Because magnesium deficiency can be seen despite a normal serum level, measurement of 24-h urine magnesium has been suggested [107]. Hypomagnesemia may lead to hypocalcemia as a result of impaired

Table 8.7

Non-Intravenous Micronutrient Supplementation in Short Bowel Syndrome

Table 8.7

Non-Intravenous Micronutrient Supplementation in Short Bowel Syndrome

Vitamin A

Oral: 5,000-30,000 IU daily; IM administration also

available

Vitamin B12

SQ/IM: 300-1, 000 pg monthly; intranasal

administration also available

Vitamin C

Oral: 250-500 mg daily

Vitamin D

Oral: 800-1,600 IU daily (or calcitriol 0.25-2 pg

daily); IM administration also available

Vitamin E

Oral: 400 U up to three times daily

Folate

Oral: 1 mg daily

Iron

Oral: 325 mg up to three times daily; IM administration

also available

Zinc

Oral: 50 mg elemental zinc (220 mg tablet) once or

twice daily

Selenium

Oral: 100 pg daily

Calcium

Oral: 1,500-2,000 mg daily

Potassium

Oral: 20-80 mEq daily

Magnesium

See text

Multivitamin

Oral: 2 capsules daily

parathyroid hormone release [108]. The correction of sodium depletion is an important factor in treating hypomagnesemia. Measurement of urinary sodium may assist in the assessment of sodium balance in some patients; a random urinary sodium concentration of <10mEq/l is generally a good indicator of sodium depletion. Oral magnesium oxide can be administered in doses of 12 to 24mEq/day and does not appear to increase stomal output, particularly when taken at night when intestinal transit is at its slowest. Finally, the oral administration of 1a-hydroxycholecalciferol can be given as it can increase both intestinal absorption and renal absorption of magnesium [109]. If moderate to severe hypomagnesemia (<1mg/dl) persists, parenteral magnesium may be necessary.

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