Role of the source of phosphate salt in improving the mineral balance of parenterally fed low birth weight infants.

Because the monobasic potassium phosphate salt (monobasic) improves the solubility of calcium and phosphorus in amino acid plus dextrose solutions, compared with the current mixtures of monobasic plus dibasic salts (dibasic), we tested the bioavailability and clinical effects of monobasic in 16 parenterally fed low birth weight infants at standard (n = 8) and high levels (n = 8) of mineral intakes. A constant infusion of macronutrients and vitamin D was provided in a crossover design of two four-day periods. With standard intakes of calcium (35 mg/kg/day, 0.9 mmol/kg/day) and phosphorus (30 mg/kg/day, 1 mmol/kg/day), there was no difference between monobasic and dibasic regimens on balance data or plasma biochemical monitoring (calcium, phosphorus, pH, carbon dioxide pressure, base excess, 1,25-dihydroxyvitamin D, 25-hydroxyvitamin D). With the use of the monobasic regimen, the mineral intakes were doubled without precipitation in the infusate: calcium, 70 mg/kg/day (1.8 mmol/kg/day), and phosphorus, 55 mg/kg/day (1.7 mmol/kg/day). This led to increased apparent retention of both calcium (63 +/- 5 mg/kg/day, 1.58 +/- 0.12 mmol/kg/day) and phosphorus (52 +/- 4 mg/kg/day, 1.67 +/- 0.14 mmol/kg/day) compared with that for standard levels of mineral intake. The improvement of calcium-phosphorus balance was accompanied by more severe calciuria (9 +/- 2 mg/kg/day, 0.2 +/- 0.05 mmol/kg/day) and by metabolic compensation for an increased acid load. In addition to the possibility of exceeding the buffering capacity of the infant, this relative acidosis could also be evidence of improved bone mineralization.

Metabolic and clinical consequences of changing from high-glucose to high-fat regimens in parenterally fed newborn infants.

To evaluate the metabolic and clinical consequences of changing from high-glucose to high-fat regimens during initiation of parenteral nutrition, we performed 22 studies in 11 newborn infants (birth weight (mean +/- SD) 2.54 +/- 0.54 kg, gestational age 37 +/- 3 weeks, postnatal age 8 +/- 3 days) maintained in a constant thermal environment. In a paired design, two isoproteinic (2.4 +/- 0.2 gm/kg/day) and isocaloric (64 +/- 6 kcal/kg/day) regimens differing by source of energy (high glucose vs high lipid) were infused on consecutive days. Environmental and body temperatures were recorded during a 4-hour period, and 24-hour urinary excretions of catecholamines, nitrogen, and C peptide were measured. Despite constant incubator and average skin temperatures, the rectal and interscapular temperatures rose significantly when the high-glucose regimen was changed to a high-lipid regimen. The specific locations of these changes in body temperature suggested brown fat activation. A significant drop in nitrogen retention (63 +/- 9% vs 56 +/- 10%) during the lipid infusion could be further evidence of a metabolic adaptation to the rapid change in energy substrates.