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Thyroxine and triiodothyronine levels are lower in preterm infants than in term infants. Until a distinction is made among hypothyroidism, prematurity, and illness as the cause, the necessity of treatment is unclear. Thyroxine, triiodothyronine, free thyroxine, and thyroid-stimulating hormone were measured weekly in 75 patients of 25 to 42 weeks gestational age. The range of thyroxine values among hospitalized term and preterm infants was lower than has been previously reported for healthy term newborns or infants. Thyroxine and triiodothyronine levels were consistently lower in preterm infants, but there were only minor differences between term and preterm infants' free thyroxine levels, which were both stable over time. Mean (SD) free thyroxine levels by week were 0.0259 (0.0079), 0.0259 (0.0057), 0.0201 (0.0066), 0.0274 (0.0079), 0.0241 (0.0023) nmol/L for term infants, and 0.0215 (0.0072), 0.0223 (0.0056), 0.0212 (0.0066), 0.0186 (0.0064), and 0.0201 (0.0021) nmol/L for preterm infants at weeks 1, 2, 3, 4, and greater than 4, respectively. Maturity was the best predictor of thyroxine or triiodothyronine levels, but illness was the clinical variable most highly correlated with free thyroxine. All 71 surviving infants were euthyroid at discharge. The free thyroxine measurement results suggest that hypothyroxinemia is not hypothyroidism but is a result of a combination of reduced protein-bound thyroxine as well as nonthyroidal illness.

Renal function was evaluated by inulin clearance (Cin) in infants weighing less than 1250 g (N = 16) during the first 72 hours of life. Their mean +/- SD gestational age (GA) was 28.5 +/- 2.2 weeks and the birthweight (BW) was 990 +/- 158 g. Eleven studies were performed on day 1, 9 on day 2, and 11 on day 3. Mean Cin were 0.27 +/- 0.23, 0.37 +/- 0.13, and 0.46 +/- 0.44 mL/kg/min on days 1, 2, and 3, respectively, but the changes were not significant. Individual Cin values ranged from 0.039 to 1.54 mL/kg/min. The Cin was lower than that observed in larger and more mature infants. There was no correlation between Cin and fractional sodium excretion (FeNa), GA, BW, or fluid intake. Fe Na did not correlate with serum sodium or sodium intake.

Necrotizing enterocolitis developed in a premature infant after a medication in elixir form, calcium glubionate, was added to his feedings. The osmolalities of this medication and four others--theophylline elixir, phenobarbital elixir, dexamethasone elixir, and digoxin elixir--were measured by freezing-point depression and compared with the osmolalities of the analogous intravenous (IV) preparations. The osmolalities of the IV preparations were much lower than those of the corresponding oral preparations, except in the case of digoxin. When clinically appropriate doses of dexamethasone and phenobarbital elixirs were mixed in volumes of formula appropriate for a single feeding for a 1,500-g infant, the osmolalities of the drug-formula mixtures increased at least 300% over formula alone. This effect was less noticeable with digoxin elixir, theophylline elixir, and calcium glubionate.

The incidence and cause of hypernatremia in twenty-five very low birthweight infants were determined by a retrospective analysis of their clinical course during the first 72 hours of life. Ten (40%) developed a serum sodium greater than or equal to 150 mEq/l. This was associated with a greater weight loss than found in normal infants (5.3 +/- 2.6%/day vs 1.7 +/- 2.3%/day, p less than .05) and with more time spent under radiant energy, but not with the amount of water, or sodium received. The severity of hypernatremia correlated with birthweight (r = -.47, p less than .05) and with postnatal weight loss but not with sodium intake. The excess weight loss in the hypernatremic group, when added to their average measured fluid intake suggests an estimated optimal fluid requirement of 150 ml/kg/day in the environment described. The hypothesized mechanism for hypernatremia is dehydration, possibly through insensible water loss.

To determine whether dexamethasone therapy altered the outcome of chronic lung disease in neonates, we conducted a prospective, randomized, placebo-controlled trial. Twenty-one 30-day-old oxygen- and ventilator-dependent infants were enrolled. The mean (+/- SD) birth weight was 808.1 +/- 141 gm and the mean gestational age was 26.0 +/- 1.5 weeks. There were 17 black and 12 male infants. Twelve received placebo and nine received dexamethasone. Neither severity of early illness, birth weight, gestational age, age when treated, gender and race distribution, nor frequency of diuretic therapy differed significantly between groups. The age at extubation, 57.2 days (placebo) versus 39.4 days (steroid), was significantly different. The average oxygen requirements of the steroid-treated patients was significantly lower than for placebo-treated patients during the first 10 days of treatment. There were no differences for placebo-versus steroid-treated patients in age when weaned to room air (95.5 days vs 74.9 days), age at discharge (119 days vs 111 days), or number of deaths (2 (17%) vs 1 (11%]. Dexamethasone therapy was associated with a significantly increased incidence of hyperglycemia (89% vs 8%) but did not influence the incidence of hypertension, intracranial hemorrhage, infection, or retinopathy of prematurity. The steroid-treated patients had a significant delay in weight gain during the first 3 weeks of treatment but recovered by discharge. Our results suggest that dexamethasone produces acute improvement in infants with lung disease but no long-term effect on mortality rate, duration of oxygen requirement or age at discharge.

The effects of aminophylline on renal function in 10 premature infants with idiopathic apnea are evaluated. The percent increases in creatinine clearance (128 +/- 339%, mean +/- SD) and sodium clearance (196 +/- 304%, mean +/- SD) are variable while the percent increase in fractional sodium excretion (69 +/- 109%, mean +/- SD) is significant. This effect is postulated to be at the proximal tubule and may be modified by the effects of postnatal age and infusion of albumin. Gestational age, birth weight, heart disease, water and sodium intake and ventilatory support did not appear to influence the results. Hyponatremia is a potential consequence of theophylline therapy for apnea.