Early Mineral Metabolism in Very‐Low‐Birth‐Weight Infants

Abstract

See ''Early Postnatal Calcium and Phosphorus Metabolism in Preterm Infants'' by Christmann et al on page 398.A voiding the development of hypophosphatemia during the first week of life could be a major issue for very-low-birthweight (VLBW) infants (1,2). Phosphate content is abundant in the cells because it represents the main anion in the intracellular space. It enters into the composition of the nucleic acids, the adenosine triphosphate, and the cell membrane (3,4). In addition to its role in bone mineralization, phosphorus (P) plays a major role in energy metabolism, acid-base status, and cellular growth, and P depletion could be associated with potential deleterious outcomes, such as nephrocalcinosis, insulin resistance (5), and nosocomial infection (6).Christmann et al (7) provide an illustration of the physiology of the mineral metabolism in preterm infants during parenteral and enteral nutrition (1,2). Calcium (Ca) and P supplies in parenteral and enteral routes are not metabolically equivalent. In parenteral nutrition, Ca and P are directly available for bone deposition as hydroxyapatite with a Ca/P molar ratio of 1.66. In addition, P is necessary for lean body mass accretion accounting for AE 0.33 mmol (10 mg) of P per gram of protein retention. In cases of relative P deficiency, available P is primarily oriented to the cellular metabolism, reducing bone mineralization or inducing bone resorption. Biochemical signs of P deficiency are the development of hypophosphatemia, hypophosphaturia, hypercalcemia, hypercalciuria, and an increase in the renal tubular reabsorption of P (TrP) > 95%.During the first week of life, Christmann et al (7) provided parenteral nutrition with a Ca/P molar ratio of 1.6 combined with human milk enriched from a starting intake of 50 mL/day onward. The combined use of a parenteral solution (PS) with a Ca/P molar ratio in the range of the bone deposition and unfortified human milk with a relative P deficiency could explain the development of the mineral metabolic disorder. Similar data were reported with the use of a PS with a Ca/P molar ratio of 2.0 and 1.2, respectively (3,6). Optimal P content in PS could be estimated on the basis of the Ca and the amino acid contents (1,3). An adequate Ca/P molar ratio would be close to 1.0 or below 1.0 in the case of high amino acid intake > 2.5/kg/day from the first day of life (1,4). Early P requirement is also increased in VLBW infants with intrauterine growth restriction (8).After the second week of life, infants were adequately fed enterally, with a minimal contribution of parenteral nutrition (7). P supplementation was still provided to more than 50% of the preterm infants during the third and fourth weeks. Mean total Ca and P intakes were approximately 3.5 mmol of Ca and 3.2 mmol Á g À1 Á day À1 of P with a Ca/P molar ratio of 1.1. This value below the recommended values for enteral nutrition (9) was associated with an increased urinary P excretion and a large reduction in the TrP below 80%, suggesting a relative P overload. During ente...

Severe hypercalcaemia and hypophosphataemia with an optimised preterm parenteral nutrition formulation in two epochs of differing phosphate supplementation

“…For preterm infants receiving PN with a higher amino acid content in the first postnatal week, an equimolar (1:1) Ca 2+ :PO 4 ratio would thus appear preferable to that currently recommended (1.3–1.7:1). Our data support current expert opinion that an adequate Ca 2+ :PO 4 molar ratio in neonatal PN in the first postnatal week should be close to or below 1.0 for higher amino acid intakes >2.5 g/kg/day starting from the first postnatal day,6 and also the suggestion that the current PN guidelines for preterm infants need revision 7…”

Electrolyte and Mineral Homeostasis After Optimizing Early Macronutrient Intakes in VLBW Infants on Parenteral Nutrition

“…It allows for the provision of early phosphorus intake of $1 mmol Á kg À1 Á day À1 from the first DOL as long as inadvertent additional sodium and potassium intakes can be limited. As suggested, the optimal Ca:P ratio seems between 0.8 and 1.0 during the first week of life and between 1.0 and 1.15 afterwards (7,8,12,40).…”

Early Hypophosphatemia in High‐Risk Preterm Infants: Efficacy and Safety of Sodium Glycerophosphate From First Day on Parenteral Nutrition

“…One of the risk factors related to hypophosphatemia is the high amino acid intake from PN in the first postnatal week . Approximately 0.33 mmol of phosphate are used for every gram of retained amino acid . In addition, amino acid infusion induces insulin secretion and a state of tissue anabolism, and consequently very early amino acid supplementation (first and second days of life) and higher concentrations of amino acids (>2–2.5 g/kg/day) given to infants at highest risk (<1000 g and intrauterine growth restriction as a result of placental dysfunction) may lead to the development of severe hypophosphatemia.…”