[Hyponatremia in very low birth weight infants]

Hyponatremia can potentially have serious effects in the premature infant, Therefore, it is important to recognize its causes and prevent it if possible. The aim of this study was to evaluate the causes of hyponatremia in very low birth weight (VLBW) infants cared for at the Neonatal Intensive Care Unit (NICU) of Children's Hospital Iceland.

Retrospective descriptive study of 20 VLBW infants at the NICU of Children's Hospital Iceland, born after <30 weeks gestation with birth weight of < or =1250 g. Information was obtained on fluid administration, weight loss, sodium administration and serum sodium concentrations during their first ten days of life.

The median gestational age was 27 weeks (24-29 weeks) and the median birth weight was 905 g (620-1250 g). A negative correlation was found between birth weight and the amount of fluids given (R2=-0.42; p=0.002). The median weight loss was 10.6% (3.1-29.5%). A positive correlation was found between weight loss and the amount of fluids the infants received (R2=0.76; p<0.001). The amount of sodium given was on the average 5.7+3.1 mmól/kg/24 hours. The median serum sodium concentration was 137 mmól/L (127-150 mmól/L). A negative correlation was found between the amount of sodium given and serum sodium concentrations (R2=-0.42; p<0.001). There was no correlation between the amount of fluids given and serum sodium concentrations (R2=0.006; p=0.7). A negative correlation was found between birth weight and serum sodium concentrations (R2=-0.24; p=0.027).

High sodium requirements in VLBW infants at our hospital suggests that their hyponatremia is mainly due to the immaturity of their kidneys, which is known to result in excessive loss of sodium in the urine.