Trace Elements

® Trace elements are essential cofactors for numerous biochemical processes. Trace elements that are added routinely to PN include zinc, selenium, copper, manganese, and chromium. There are various commercial parenteral trace-element formulations that can be added to PN admixtures (e.g., MTE-5). Zinc is important for wound healing, and patients with high-output fistulas, diarrhea, burns, and large open wounds may require additional zinc supplementation. Patients may lose as much as 12 to 17 mg zinc per liter of GI output (e.g., from diarrhea or enterocutaneous fistula losses); however, 12 mg/day may be adequate to maintain these patients in positive zinc bal-

ance. Patients with chronic severe diarrhea, malabsorption, and short-gut syndrome may also have increased selenium losses and may require additional selenium supplementation. Chromium is a cofactor for glucose metabolism, and patients with chromium deficiency may exhibit glucose intolerance; however, chromium deficiency is a rare cause of hyperglycemia. Patients with cholestasis (serum direct bilirubin concentration that exceeds 2 mg/dL [34.2 |imol/L]) should have manganese and possibly copper restricted to avoid their accumulation and possible toxicity, because both elements undergo biliary elimination. Manganese-induced neurotoxicity has been reported in PN patients with cholestasis and those receiving chronic PN. However, copper deficiency resulting in anemia, pancytopenia and death has occurred when copper was omitted from the PN of PN-dependent patients. Because copper deficiency has been reported to occur anywhere between 6 weeks and 12 months following copper elimination from PN,18 serum copper concentrations need to be regularly monitored (e.g., every 6 weeks at first and 2-3 months thereafter) when copper is omitted from PN admixtures. Trace element status should be monitored at first periodically (e.g., every 2-3 months) in patients at risk for trace element deficiency or accumulation. Once stable, serum trace element concentrations can be monitored less frequently (e.g., every 6-12 months).

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