PHYSICOCHEMICAL STABILITY OF TOTAL NUTRIENT ADMIXTURES

The effect of six independent factors on the stability of i.v. nutriti onal emulsions was studied. Forty-five i.v. nutritional admixtures wer e prepared, each containing the following: (1) amino acids (range, 2.5 -7%), (2) hydrated glucose (range, 5-20%), (3) lipid emulsion (range, 2-5%), (4) monovalent cations (range, 0-150 meq/L), (5) divalent catio ns (range, 4-20 meq/L), and (6) trivalent cations (range, 0-10 mg of e lemental iron/L). Stability assessments included particle-size analysi s, pH determination, and visual inspection. Sizing and counting of fat particles was achieved by using light obscuration and dynamic light s catter methods. Light obscuration and visual assessments were performe d at 0, 6, 12, 24, and 30 hours. Dynamic light scatter and pH determin ations were performed at 0 and 30 hours. Multiple stepwise regression analysis revealed that trivalent cation concentration was the only var iable that affected the stability of nutritional emulsions (p<0.00001) , accounting for approximately 60% of the potentially dangerous increa ses in fat particle sizes observed. In addition, a percentage of large fat particles (>5 mu m in diameter) greater than 0.4% was associated with unstable emulsions. However, this instability was visibly evident only 65% of the time. Changes in mean globule diameter, cream-layer t hickness, and pH did not reveal instability in these emulsions. Emulsi ons in which >0.4% of the initial fat concentration consists of partic les of >5 mu m in diameter are likely to become unstable. Of the six f actors studied, the trivalent cation in iron dextran was most disrupti ve to lipid-based parenteral nutrient admixtures.