Effect of fat emulsion and supersaturation on calcium phosphate solubility in parenteral nutrient admixtures

The calcium concentration in 0.2 micrometer porosity membrane filtrates of parenteral nutrient admixtures (PNAs) was measured by atomic absorption spectroscopy. The PNAs contained 22% dextose, 2.7% crystalline amino acids; 0% to 3.2% safflower and soybean oils from intravenous fat emulsion, 19-24 mEq/L calcium gluconate, and 22-28 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 micrometers 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 phophates should be infused through a sterile filter with appropriate mean microporosity, eg, usually 1.2 micrometer for fat emulsion-containing and 0.2 or 0.45 micrometer for fat-free formulations.