Der Stoffwechsel bei intraven�ser Applikation von N�hrl�sungen, insbesondere synthetisch zusammengestellter Aminos�urel�sungen

Parenteral nutrition in the ICU: Lessons learned over the past few years

Since the early 1990s enteral nutrition (EN) has been considered the optimal route of feeding rather than parenteral nutrition (PN), which was considered harmful in critically ill patients with intense inflammation. The aim of this review was to summarize recent developments and progress in PN, which have changed the view on this feeding technique. PubMed and personal databases were searched for studies and reviews reporting historical development of PN, and for clinical trials conducted after 2010 investigating PN in critical illness, comparing it to EN or not. Trials from the past decade have explored modalities and timing of artificial feeding. Trials based on equation-estimated energy targets and applying an early full feeding strategy have generally had negative results in terms of complications (infections, prolonged ventilation, and intestinal complications with EN). The few trials that based their targets on measured energy targets have achieved reduction of complications regardless of the route. Opposing enteral and parenteral feeding is no longer rational in the critical care setting. A pragmatic and reasonable approach offers better options for the individual patient. Although PN is simpler to deliver than EN, its metabolic consequences are more complicated to handle. A combination of both techniques may be a more reasonable approach in the sickest patients.

Liquid chromatographic determination of D-amino acids in cheese and cow milk. Implication of starter cultures, amino acid racemases, and rumen microorganisms on formation, and nutritional considerations

Free L- and D-amino acids (L-AA, D-AA) were isolated from an Appenzeller cheese, from raw milk, and from an ethanolic extract as well as a total hydrolysate of cow's rumen microorganisms, and their relative amounts were determined by reversed-phase high-performance liquid chromatography after derivatization witho-phthaldialdehyde together withN-isobutyryl-L-(or D)-cysteine. D-Ala, D-Asp and D-Glu were found, among other D-AA in all cases and a microbial origin of free D-AA found in cheese and milk was rationalized. From the results, and taking other findings of the occurrence of D-AA in food and beverages into account, the highest intake of D-AA is to be expected from the consumption of ripened cheeses. From the presence of D-amino acid oxidases in human kidney, liver, and brain and from reports on the intravenous administration of racemic AA to humans and their metabolisation it is concluded that intake of free D-AA found in food is no threat for human beings.

Determination of amino acid enantiomers in human urine and blood serum by gas chromatography-mass spectrometry

Amino acid (AA) enantiomers were determined as N(O)-pentafluoropropionyl-(2)-propyl esters by chiral gas chromatography-mass spectrometry (GC-MS) in 24 h samples of the urine of three healthy volunteers and in their blood sera. In urine the largest amounts were determined for D-Ser (64-199 micromol/day) and D-Ala (24-138 micromol/day). In blood sera, D-Ala (2.3-4.2 micromol/L) and D-Ser (1.0-2.9 micromol/L) were most abundant. Varying amounts of the D-enantiomers of Thr, Pro, Asx, Glx, Phe, Tyr, Orn and Lys were also found, albeit not in all urines and sera. Further, enantiomers were quantified in urine samples of two volunteers fasting for 115 h. Quantities of renally excreted D-AAs decreased in fasting, although amounts of D-Ser (69 and 77 micromol/L urine) as well as other D-AAs were still detectable. Time-dependent analyses of urine showed that D-AAs are continuously excreted.

Food energy values of artificial feeds for man

The gross and metabolizable energy values of artificial enteral and parenteral feeds have been calculated from detailed composition data for amino acid, fatty acid, saccharide and other oxidizable substrates and compared with similar values calculated for conventional foods. The background to the derivation and application of calorie conversion factors is briefly reviewed. There is evidence of widespread inappropriate application of calorie conversion factors for carbohydrates and amino acid mixtures. Appropriate digestibility or availability factors for the oxidizable fractions of artificial feeds is discussed for normal adult man and the intrinsic difficulty of obtaining availability values for subjects with varying types of malabsorption or urinary and tissue losses is emphasized. The nitrogen:protein conversion ratio and the availability of energy at a biochemical level (i.e. net ATP yield per calorie) is also considered. Finally, a more uniform and appropriate approach to calculating energy values for artificial feeds for the purposes of labelling, product description and estimating energy intake of patients is called for.

Partial substitution of amino acids of a parenteral solution with tripeptides: effects on parameters of protein nutrition in baboons

We previously showed that triglycine and trileucine are efficiently utilized when infused intravenously (IV) in baboons who are fed a complete diet orally. In the present experiments we investigated the utilization of these tripeptides in the context of total parenteral nutrition. A group of subhuman primates (baboon) was subjected sequentially to two forms of total parenteral nutrition, each for a period of six days. The only difference between the two periods was that in one, all amino acids were given in free form, and in the other, the glycine and leucine components of the amino acid mixture were replaced with triglycine and trileucine, respectively. During both experimental periods the infusion solution provided daily 100 calories/kg body weight and 2.5 g amino acids/kg body weight. There were no significant differences between nitrogen balance, plasma amino acid concentrations, or urinary excretion of amino acids for the two forms of parenteral nutrition. The only exceptions were a greater plasma concentration of isoleucine and a greater urinary excretion of leucine during infusion of the partial peptide solution. Assimilation of triglycine and trileucine under the conditions of total parenteral nutrition was assessed by determining concentrations of these peptides in plasma and urine. Trileucine was not found in plasma, and only 1.8% of the amount of trileucine infused appeared as trileucine and dileucine in urine. Triglycine was detected in plasma and 17.1% of the amount of triglycine infused was excreted in urine as triglycine and diglycine. These data suggest that assimilation of trileucine and triglycine under the conditions of our experiment was sufficiently efficient to meet the daily need for an essential amino acid (leucine) and for nitrogen (glycine).

D-amino acid utilization in infants measured with the 15N-tracer technique

The utilization rates of D-[15N] valine, D-[15N] leucine, D-[15N] phenylalanine and D-[15N] alanine were investigated in seven infants being fed parenterally. Retention of the (15)N in the protein pool varied from one amino acid to another and ranged from 23.2% for D-[15N] valine to 48.6% for D-[15N] alanine. In the case of valine it was shown that cumulative renal excretion amounted to 70% of the applied (15)N-dose, 44% being overflow of unchanged D-[15N] valine, 16.6% appearing as [15N] urea and 1.2% as [15N] ammonium. This indicates that doubling the concentrations of D-amino acid racemates compared with their L-isomer counterparts in parenteral feeding solutions must inevitably lead to imbalances. The use of D-amino acids for the purposes of parenteral nutrition remains however ineffective due to their poor and variable utilization compared to L-amino acids.