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Effect of Fat Emulsion and Supersaturation in Parenteral Nutrition Admixtures

Author(s):  Fausel Christopher A, Newton David W, Driscoll David F, Allen Loyd V Jr

Issue:  Jan/Feb 1997 - Hospice Care
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Abstract:  The calcium concentration in 0.2-µm porosity membrane filtrates of parenteral nutrient admixtures (PNAs) was measured by atomic absorption spectroscopy. The PNAs contained 22% dextrose, 2.7% crystalline amino acids; 0% to 3.2% safflower and soybean oils from intravenous fat emulsion, 19 to 24 mEq/L calcium gluconate, and 22 to 28 mmol/L sodium phosphates. The calcium and phosphates concentrations caused visible precipitation of dibasic calcium phosphate, CaHPO4, in all fat-free samples. The results were the following: (1)Fat-free PNAs containing FreAmine III 8.5% with electrolytes resulted in supersaturation of CaHPO4 from which CaHPO4 continued to precipitate for 14 days after three successive 0.2-µm porosity filtrations; (2) egg-yolk phospholipids caused a statistically insignificant 1% to 11% increase in calcium solubility; (3) at the same pH, the calcium solubility was 10% higher in 2.7% amino acids and 22% dextrose than in 22% dextrose alone.

The growth kinetics of CaHPO4 crystals in PNAs do not appear to be predictable. Both transient and permanent precipitation of CaHPO4 can result when the product of the Ca+2 and HPO4-2 ion concentrations exceeds the solubility product (Ksp) of CaHPO4 either before or after the compounding of a PNA is completed.

Both transient precipitation at subsaturated and permanent precipitation at saturated and supersaturated CaHPO4 concentrations can be clinically dangerous. All PNAs containing calcium and inorganic phosphates should be infused through a sterile filter with appropriate mean microporosity, eg, usually 1.2 µm for fat emulsion-containing and 0.2 or 0.45 µm for fat-free formulations.


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