Urinary mineral excretion in preterm neonates during the first month of life

Sodium Intake Requirements for Preterm Neonates: Review and Recommendations

It is widely accepted that sodium is an essential nutritional electrolyte and its deficiency is associated with neurological sequelae and poor growth. The provision of an adequate sodium intake to preterm neonates is hampered by the technical difficulty in clinically assessing total body sodium content. As addressed in this review, there is a lack of consensus on the definition of hyponatremia early in life, but there is no evidence that it should deviate from the widely accepted normative data for adult subjects. A low urinary sodium content is accepted by many as reflecting total body sodium deficiency, yet spot urinary sodium measurements are of questionable clinical value. The hormonal regulation of sodium homeostasis is here reviewed and the mechanism accounting for sodium deficiency-induced growth impairment in preterm infants addressed. Lastly, we provide evidence-based gestational and postnatal age-dependent recommendations for the provision of adequate sodium intake to preterm neonates.

Changes in Biochemical Parameters of the Calcium-Phosphorus Homeostasis in Relation to Nutritional Intake in Very-Low-Birth-Weight Infants

Preterm infants are at significant risk to develop reduced bone mineralization based on inadequate supply of calcium and phosphorus (Ca-P). Biochemical parameters can be used to evaluate the nutritional intake. The direct effect of nutritional intake on changes in biochemical parameters has not been studied. Our objective was to evaluate the effect of Ca-P supplementation on biochemical markers as serum (s)/urinary (u) Ca and P; alkaline phosphatase (ALP); tubular reabsorption of P (TrP); and urinary ratios for Ca/creatinin (creat) and P/creatinin in Very-Low-Birth-Weight infants on Postnatal Days 1, 3, 5, 7, 10, and 14. This observational study compared two groups with High (n = 30) and Low (n = 40) intake of Ca-P. Birth weight: median (IRQ) 948 (772–1225) vs. 939 (776–1163) grams; and gestational age: 28.2 (26.5–29.6) vs. 27.8 (26.1–29.4) weeks. Daily median concentrations of biochemical parameter were not different between the groups but linear regression mixed model analyses showed that Ca intake increased the uCa and TrP (p = 0.04) and decreased ALP (p = 0.00). Phosphorus intake increased sP, uP and uP/creat ratio and ALP (p ≤ 0.02) and caused decrease in TrP (p = 0.00). Protein intake decreased sP (p = 0.000), while low gestational age and male gender increased renal excretion of P (p < 0.03). Standardized repeated measurements showed that biochemical parameters were affected by nutritional intake, gestational age and gender.

Impact of Early Sodium Supplementation on Hyponatremia and Growth in Premature Infants: A Randomized Controlled Trial

BACKGROUND

We tested the hypothesis that sodium supplementation in early preterm infants prevents late-onset hyponatremia and improves growth without increasing common morbidities during birth hospitalization.

MATERIALS AND METHODS

This was a randomized, masked controlled trial of 4 mEq/kg/d of sodium (intervention) versus sterile water (placebo) from days-of-life 7 to 35 in infants born at <32 weeks corrected gestational age. The primary outcome was weight gain in the first 6 weeks of life. Secondary outcomes included weekly serum sodium concentrations, growth in body length and head circumference, and complications of prematurity during birth hospitalization.

RESULTS

Fifty-three infants with an average corrected gestational age of 28.5 ± 2.4 weeks were randomized. Infants receiving the intervention had fewer (P = .012) reports of serum sodium concentrations <135 mmol/L and greater velocity of weight gain during the study period, mean (SD) 26.9 (3.1) vs 22.9 (4.7) g/kg/day, P = .012. At 6 weeks of age, infants <28 weeks' gestation who received sodium supplementation had greater percentage weight change from birth, mean (SD) 193% (22%) vs 173% (10%), P = .041, and maintained fetal reference birth percentile for body weight more often (P = .002) compared with infants receiving placebo. Growth in length and head circumference was not significantly different between study arms. No increase in common prematurity-related morbidities was detected in infants who received supplemental sodium chloride.

CONCLUSION

Sodium supplementation of enteral feedings in very premature infants averts hyponatremia and enhances weight gain.

Monitoring of urinary calcium and phosphorus excretion in preterm infants: comparison of 2 methods

OBJECTIVES

Premature babies require supplementation with calcium (Ca) and phosphorus (P) to prevent metabolic bone disease of prematurity. To guide mineral supplementation, 2 methods of monitoring urinary excretion of Ca and P are used: urinary Ca or P concentration and Ca/creatinine (Crea) or P/Crea ratios. We compare these 2 methods in regards to their agreement on the need for mineral supplementation.

METHODS

Retrospective chart review of 230 premature babies with birth weight <1500 g, undergoing screening of urinary spot samples from day 21 of life and fortnightly thereafter. Hypothetical cutoff values for urine Ca or P concentration (1 mmol/L) and urine Ca/Crea ratio (0.5 mol/mol) or P/Crea ratio (4 mol/mol) were applied to the sample results. The agreement on whether to supplement the respective minerals based on the results with the 2 methods was compared. Multivariate general linear models sought to identify patient characteristics to predict discordant results.

RESULTS

A total of 24.8% of cases did not agree on the indication for Ca supplementation, and 8.8% for P. Total daily Ca intake was the only patient characteristic associated with discordant results.

CONCLUSIONS

With the intention to supplement the respective mineral, comparison of urinary mineral concentration with mineral/Crea ratio is moderate for Ca and good for P. The results do not allow identifying superiority of either method on the decision as to which babies require Ca and/or P supplements.

Sodium supplementation in neonates with pierre robin sequence significantly improves weight gain if urinary sodium is low

OBJECTIVE

To investigate whether sodium supplementation increases weight gain in babies with grade 3 Pierre Robin sequence if their urinary sodium is low.

DESIGN

Retrospective review of all medical, dietitian, and nursing notes of babies admitted from 2000 to 2007, inclusive.

SETTING

Tertiary center for cleft care.

PATIENTS

A total of 33 babies requiring nasogastric and nasopharangeal intubation for Pierre Robin sequence were identified. Those for whom weights could not be measured accurately (n  =  4) were excluded from further study.

INTERVENTIONS

Urinary sodium was low and weight gain poor in 21 of the remaining 29 babies (72%), and oral sodium supplementation was given to establish and maintain a normal urinary sodium (10 to 20 mmol/L).

MAIN OUTCOME MEASURE

Mean daily weight gain.

RESULTS

The mean daily weight gain of the 18 babies with low urinary sodium admitted in the first few days of life improved from 20 to 34 g (p < .001) following oral sodium supplementation. This gave a mean difference of 14 g (lower quartile  =  6 g, upper quartile  =  25 g, 95% confidence interval  =  20, 90% confidence interval  =  10). The mean daily weight gain of the eight patients who did not require sodium supplementation was 33.6 g.

CONCLUSIONS

Urinary sodium tests are simple and noninvasive and allow monitoring of urinary sodium. If low, adequate supplementation improved weight gain (p < .001), reversing failure to thrive in babies with severe Pierre Robin sequence. These findings have been unreported previously.

Nephrocalcinosis in preterm neonates

The prevalence of nephrocalcinosis (NC) in preterm neonates in recent reports is 7-41%. The wide range in prevalence is a consequence of different study populations and ultrasound equipment and criteria, in addition to a moderate interobserver variation. NC in preterm neonates has a multifactorial aetiology, consisting of low gestational age and birth weight, often in combination with severe respiratory disease, and occurs as a result of an imbalance between stone-promoting and stone-inhibiting factors. A limited number of histological studies suggest that calcium oxalate crystals play an important role in NC in premature neonates. In 85% of children resolution of NC occurs in the first years of life. Prematurity, per se, is associated with high blood pressure, relatively small kidneys, and (distal) tubular dysfunction. In addition, NC in preterm neonates can have long-term sequelae for glomerular and tubular function. Long-term follow-up of blood pressure and renal function of prematurely born children, especially with neonatal NC, is recommended. Prevention of NC with (low) oral doses of citrate has not resulted in a significant decrease in the prevalence of NC; a higher citrate dosage deserves further study. Future research pertaining to prevention of NC in preterm neonates is crucial.