Late hyponatremia in very low birthweight infants. (less than 1.3 kilograms).

Late hyponatremia (plasma Na+ less than 130 mEq/liter) occurred frequently (on 54 of 159 occasions) in 46 very low virthweight (VLBW) infants (less than 1.3 kg at birth) between 2 and 6 weeks of age while receiving a sodium intake of less than or equal to 2 mEg/kg/24 hr. To elucidate possible pathogenetic mechanisms five groups of such infants were studied while receiving a commercially available formula reconstituted to give two different volumes and two different Na+ concentrations. Sodium intake in the nonsupplemented (NS) infants (n = 23) was less than 2 mEq/kg/24 hr. Supplemented (S) infants (n = 16) received approximately 3 mEq Na+/kg/24 hr. A further group of seven infants given a high volume (200 ml/kg/24 hr), high caloric (100 cal/dl) formula and Na+ supplementation (to 3 mEq/kg/24 hr) was also included. Infants were studied from age 14 days until they weighed 1.80 +/- 0.05 kg at a mean age of 47 days. At the time of start of the study, 6 of 20 NS and 6 of 19 S infants were hyponatremic. After supplementation only two episodes of hyponatremia occurred in S infants, both during the first study week, whereas the high incidence of hyponatremia in NS infants period. During baseline urine collections all infants excreted between 80 and 100 ml/kg/24 hr urine, but those receiving 150 ml/kg/24 hr formula decreased their urinary output rapidly to 50 ml/kg/24 hr, whereas infants receiving high volume feeds (200 ml/kg/24 hr) did not decrease their urinary output until the third balance at an average age of 45 days. All infants excreted between 1.0 and 1.2 mEq/kg/24 hr of sodium in their urine during the initial collection. Nonsupplemented infants reduced their urinary Na+ excretion more rapidly than supplemented babies (NS: from 1.03 to 0.55 mEq/kg/24 hr, first vs second balance; S: from 1.00 to 0.80 mEq/kg/24 hr, first vs third balance). Mean potassium excretion remained unchanged in NS and S infants during the study period and was not affected by the volume or caloric content of the formula. Extracellular volume (ECV) and total body water (TBW) were measure serially, and there were no differences between S and NS infants in the distribution of body water. The percentage of TBW and ECV decreased in all groups with increasing postnatal age.

Growth and mineral metabolism in very low birth weight infants. I. Comparison of the effects of two modes of NaHCO3 treatment of late metabolic acidosis.

Twenty-six infants weighing less than 1,300 g at birth were divided into pairs according to birth weight (900-1,100 and 1,101-1,300 g) and gestational age ("appropriate" (AGA) = mean 31 weeks; and "small" (SGA) = mean 34 weeks). One member of the pairs was then allocated randomly to one of two treatment regimens with oral sodium bicarbonate. Group A was treated whenever base excess was greater than -8mEq/liter as detected on twice weekly testing and/or when suspected to be acidotic from failure to gain weight. In group B, base excess was maintained within 1 SD of normal (-3.2 +/- 1.7 mEq/liter). The infants received Enfalac 200 ml/kg/24 hr, at 67 cal/100 ml, with vitamin D 400 IU/24 hr added from age 2 weeks. The following measurements were made: daily weight, weekly length, skinfold thickness, head circumference, twice weekly blood pH, PaCO2, base excess, and weekly plasma total calcium, ionic calcium, total magnesium, inorganic phosphorus, and total protein. There were six pairs of each of AGA and SGA infants and two unpaired group A infants. Weekly weight gains did not differ between group A and group B or between AGA and SGA. Length increment was greater in AGA than in SGA babies (0.94 +/- 0.02 vs 0.85 +/- 0.04 cm/week) but not significantly so (P less than 0.1), and in group B babies compared to group A babies (0.973 +/- 0.029 vs 0.83 +/- 0.037 cm/week) (P less than 0.01). Plasma pH was lower in group A (7.23 +/- 0.02) than in group B (7.30 +/- 0.02) and calcium ion activity higher (group A 2.72 +/- 0.04; group B 2.51 +/- 0.06 mEq/liter) between ages 20 and 29 days. Plasma magnesium was higher in group A (1.77 +/- 0.04 mEq/liter) than in group B (1.56 +/- 0.06 mEq/liter) from age 20 to 39 days. Inorganic phosphorus concentrations were consistently higher in group A than in group B, but the differences did not reach significance. Mean total protein concentrations did not rise above 4.5 g/100 ml and tended to be higher in babies of group A than of group B. Bone age was retarded in all babies. Radiographs available for 7 of 13 SGA infants were normal, whereas 6 of 11 radiographs of AGA babies showed some osteoporotic changes.

Growth and mineral metabolism in very low birth weight infants. II. Effects of calcium supplementation on growth and divalent cations.

Infants of two groups, one of 16, one of 14 infants, who weighed less than 1.3 kg at birth (mean 1.01 +/- 0.05 kg), were studied from age 14 days until they reached 1.8 kg body weight. Infants were pair-matched for gestational age and birth weight and one member was randomly allocated to two treatment groups. Infants in group A received no calcium supplement and those in group B received calcium lactate, 800 mg/kg/24 hr hr, in divided doses with each feed. All were fed "Improved" SMA, 200 ml/kg/24 hr, 160 cal/kg/24 hr, and were given a multivitamin preparation containing 500 IU vitamin D2/dose. The infants' weekly length gain did not differ between groups (1.08 +/- 0.04 cm/week vs 1.11 +/- 0.04 cm/week; mean +/- SEM). Mean weight and head cercumference increments also were similar (group A, 163 +/- 6 g/week; 1.12 +/- 0.03 cm/week; group B, 170 +/- 6 g/week and 1.18 +/- 0.03 cm/week). An increase in blood pH from 7.33 +/- 0.01 to 7.41 +/- 0.01 (P less than 0.01) in group A babies was associated with a decrease in PCO2 from 44.2 +/- 1.0 to 38.9 +/- 1.4 mm Hg. Values remained unchanged with age in group B babies...