New insights into the methodological issues of the indicator amino acid oxidation method in preterm neonates

Background: We determined the effect of adaptation to the study diet on oxidation of the indicator amino acid and the required tracer washout time in preterms. Methods: Subjects received a study diet for 6 d that entailed a 50% reduction in leucine. Tracer studies using enterally infused [ 13 C]bicarbonate and [1-13 C]phenylalanine were performed on days 1, 2, 4, and 6. Breath samples containing 13 CO 2 were collected during steady state and measured by infrared spectrometric analysis, and the fraction of 13 CO 2 recovery from 13 C oxidation (F 13 CO 2) was calculated. Results: Preterm infants (n = 11, birth weight 1.9 ± 0.1 kg, gestational age 32.6 ± 1.5 wk) received 166 mg/kg/d of leucine. Baseline enrichment changed significantly at day 1 of the study diet. F 13 CO 2 did not change significantly between days 2 and 4 but was significantly lower at day 6. The tracer washout time was determined to be 7.5 h using a biphasic regression analysis. Conclusion: One day of adaptation to a new diet is necessary to adapt to the 13 C enrichment of the study formula before starting infant requirement studies. Adaptation for a period of 5 d results in a protein-sparing response. The minimal time between two studies within the same subject is 7.5 h. © 2013 International Pediatric Research Foundation, Inc

Majority of dietary glutamine is utilized in first pass in preterm infants

Glutamine is a conditionally essential amino acid for very low-birth weight infants by virtue of its ability to play an important role in several key metabolic processes of immune cells and enterocytes. Although glutamine is known to be used to a great extend, the exact splanchnic metabolism in enterally fed preterm infants is unknown. We hypothesized that preterm infants show a high splanchnic first-pass glutamine metabolism and the primary metabolic fate of glutamine is oxidation. Five preterm infants (mean ± SD birth weight 1.07 ± 0.22 kg and GA 29 ± 2 wk) were studied by dual tracer ([U-C]glutamine and [N2]glutamine) cross-over techniques on two study days (at postnatal week 3 ± 1 wk). Splanchnic and whole-body glutamine kinetics were assessed by plasma isotopic enrichment of [U-C]glutamine and [N2]glutamine and breath CO2 enrichments. Mean fractional first-pass glutamine uptake was 73 ± 6% and 57 ± 17% on the study days. The splanchnic tissues contributed for a large part (57 ± 6%) to the total amount of labeled carbon from glutamine retrieved in expiratory air. Dietary glutamine is used to a great extent by the splanchnic tissues in preterm infants and its carbon skeleton has an important role as fuel source. Copyright © 2010 International Pediatric Research Foundation, Inc

Feeding Very-Low-Birth-Weight Infants: Our Aspirations versus the Reality in Practice

Recently, new guidelines for enteral feedings in premature infants were issued by the European Society of Pediatric Gastroenterology, Hepatology, and Nutrition Committee on Nutrition. Nevertheless, practice proves difficult to attain suggested intakes at all times, and occurrence of significant potential cumulative nutritional deficits 'lies in wait' in the neonatal intensive care unit. This review describes several aspects that are mandatory for optimizing nutritional intake in these vulnerable infants. These aspects range from optimal infrastructure to the initiation of parenteral nutrition with proper transition to enteral breast or formula feedings. Proper monitoring of nutritional tolerance includes serum biochemistry although proper specific markers are unknown and safety reference values are lacking. Although a lot of progress has been made through research during the last few decades, numerous questions still remain unanswered as to what would be the optimal quantity and quality of the various macronutrients. The inevitable suboptimal intake may, however, contribute significantly to the incidence of neonatal diseases, including impaired neurodevelopment. Therefore, it is pivotal that all hospital staff acknowledges that preterm birth is a nutritional emergency and that all must be done, both in clinical practice as well as in research, to reduce nutritional deficit