Since over two decades it is well-known that good availability of nutrients can be reached by simultaneous administration of macronutrients. Clinical nutrition therefore is made by use of nutrient admixtures. Should we concentrate to the intravenous nutrition, these solutions are basically composed of amino acids, glucose and fat emulsions therefore they are called as all-in-one mixtures. Usually, additional important ingredients like electrolytes, trace elements and vitamins, are also concomitantly admixed and the final product is named as total parenteral nutrient (TPN) mixture 1. There are special conditions (e.g. high risk of tetanic contraction or electrolyte depletion in case of cardiac surgery with extracorporeal circulation) when extra electrolytes are needed. Typically Ca²⁺ and phosphate are the boosted ions out of which Ca²⁺ is more dangerous in oil-containing mixtures due to the bivalent cation property that can damage lipid-droplet surface charge and so the repulsive force. TPN infusions are usually administered during a treatment period of 10–24 hours per day due to the metabolic capacity of the liver.

During this time interval physicochemically stable TPN solution (emulsion) is needed for the treatment. In our previous studies the droplet size stability of all-in-one nutritive mixtures containing different fat emulsions were studied. Authors concluded that droplet stability of MCT/LCT lipids surpassed the pure LCT 2 and the SMOF-lipid was more stable than that of MCT/LCT 3. In our present study we broadened the range of lipids with olive-oil containing emulsion. The olive oil consists of mainly MUFA that has a lot of beneficial properties, primarily the stability against lipid-peroxidation 4. This is important in case of storage because in the plastic (EVA) bags used for storage of TPNs peroxidation of lipids is much more pronounced than that in glass bottles 5. In human studies, however the protective action against oxidative stress is controversial 67. Aging process in oil-containing colloid systems may increase critical flocculation concentration of eg. Ca²⁺ in the emulsions 8 and the lipid-peroxidation can play a role in the aging processes of colloid systems like oil-containing TPNs, this property of olive oil can be of importance in case of kinetic/physical stability of all-in-one nutrient mixtures however, we did not study the details of aging process itself in this experiment.

The aim of the present study was to demonstrate any clinically significant physicochemical difference between two TPNs containing LCT-based lipid emulsion regarding the droplet-size and zeta potential.

Total parenteral nutrition admixtures are colloid dispersion systems, where droplet-size should be under 5 μm in long-term. This size limit remains under the human red blood cell diameter (6–8 μm) and so producers and users can avoid occlusion of capillaries due to the fat-droplets in the infusion. Stable lipid-emulsions used in the iv therapy are usually monodisperse systems with a mean droplet diameter of 200–600 nm, and according to the Gauss-distribution with lower and upper limits of 95% at ca. 50 and 1000 nm respectively. According to the USP droplets with diameter higher than 5 μm are still allowed in parenteral lipid emulsions and in therapeutic admixtures but they must not exceed the proportion of 0.05% 9. In emulsions used as human pharmaceuticals the droplets are usually stabilized with any type of lecithin. The Stern-layer around the small fat globules in the water-based emulsions like all-in-one iv nutritions, is a stable interface where the surrounding ions are strongly bound to the globules. The stability of this system depends on the repulsive and attractive colloidal forces, such as van der Waals, electrical double-layer and steric forces that act between the droplets. The repulsive force on the surface of the fat droplet can be measured as zeta-potential. In case of this type of emulsions negative charge of oil droplets below −30 mV means that the system is stable enough to be used for intravenous nourishment of patients 10. Should we affect the density of the Stern-layer around the droplets by altering the conductivity (eg. addition of bivalent cations) we jeopardize the stability of the whole system, therefore monitoring of zeta-potential and the droplet-size in a new composition is essential before using it for treatment of patients.

Industrial convenience systems of OliClinomel N6-900 E (Baxter) and Kabiven (FreseniusKabi) were used as all-in-one nutrient mixtures. OliClinomel contains 80% of olive oil (LCT, in 60-80% esterified by C18-MUFA of the ω-9 subgroup) and 20% of soybean oil (LCT, mainly triglyceride esters composed of C-18:2 PUFA of the ω-6 subgroup). Kabiven contains 100% soybean oil (LCT, mainly C18:2 PUFA esters). The three-chamber bags were reconstituted according to the instruction for use by breaking the non-permanent seals between the compartments and then mixing them by inverting the bag 10.

An overdose of Ca-gluconate (25 ml into 1000 ml out of 100 mg/ml injection = 5.5 mmol/l Ca²⁺ extra) was added during the preparation process to one of the TPN. Ingredients in g/l and mmol/l after reconstitution and additional Ca-gluconate are as follows:

OliClinomel (samples OA and OC) Macronutrients: 34 g/l Amino acids, 120 g/l Glucose, 40 g/l FatMicronutrient: 32 mmol/l Na⁺, 24 mmol/l K⁺, 2.2 mmol/l Mg²⁺, 2 mmol/l (Sample OA) and 7.5 mmol/l (Sample OC) Ca²⁺, 10 mmol/l Phosphate, 53 mmol/l Acetate and 46 mmol/l Cl^-.

Kabiven (samples KA and KC) Macronutrients: 33 g/l Amino acids, 100 g/l Glucose, 39 g/l FatMicronutrients: 31 mmol/l Na⁺, 23 mmol/l K⁺, 3.9 mmol/l Mg²⁺, 1.9 mmol/l (Sample KA) and 7.4 mmol/l (Sample KC) Ca²⁺, 9.7 mmol/l Phosphate, 3.9 mmol/l Sulphate, 38 mmol/l Acetate and 45 mmol/l Cl^-.

Previously it was found that a moderate difference (up to 20%) in glucose content did not influence the droplet-stability under very similar electrolyte-environment 3. So we can state that the two TPN systems studied in our present experiments are comparable. Test mixtures signed with C contain ca. 50% more Ca²⁺ than maximally advised by the manufacturers and it was considered the possible upper limit of Ca²⁺ content in the comparison of the stability of different mixtures.

After shaking the solution container, it has been connected to an infusion set and hanged up to an infusion stander. Light protection was not used and the storage temperature was hospital ward room-temperature (22–24°C). After a lag time of 5 minutes infusion administration with a speed of 2 ml/min (= 120 ml/hours) has been started. Samples for droplet-size control measurements were taken from the “supernatant” of the infusion bag content (within 3 mm of the surface, later mentioned as “upper level sample” signed as “up”) and from the infusion tube 25 cm after the output port of the container bag (“lower level sample” in short “low”). Samples (5 ml) have been taken just after the start (zero point) and 24 hours later (end point). For zeta-potential measurements we took samples from the middle of the container and sampling was done at start, after 1, 2, 3, 10, 11, 12 hours to simulate the real parenteral nutrition conditions and in the end of the study period (24. hour).

Droplet size measurements were performed by photon-correlation spectroscopy (PCS, made by Zetasizer 4 and Nanosizer ZS, Malvern Instruments, England) and the surface-charge was checked by measurement of electrophoretic movement (Laser Doppler Anemometry by Zetasizer 4, Malvern Instruments, England). Droplet size distributions and zeta-potential figures were made out of 2 or 3 separate samples in each measurement depending on the coherence of measurement results. Nature samples were diluted by purified water in a proportion of 1:300 in order to reach the measurement concentration-range according to the manual for use of the equipment. The measurement limits of the Zetasizer 4 equipment are 3-3000 nm for determination of droplet size and 20-20000 nm in case of LDA 11. The measuring range of the Zetasizer Nano ZS equipment (Dynamic Light Scattering principle) for particle size measurement is between 0.3 nm-10 μm and for zeta-potential 3.8-100000 nm 12. We expected the 99.5% of droplets in the range of 10-3000 nm with the main peak between 300-700 nm and the critical point was the size over 5 μm. Surface charge of droplets was expected between −40 and −10 mV. Droplet-size control was performed according to the accepted rules based on the USP 1314. We also controlled the droplet stability by electrokinetic (zeta-potential) measurement as advised 15.