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Aim: 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 birht weight (VLBW) infants cared for at the Neonatal Intensive Care Unit (NICU) of Children?s Hospital Iceland.

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

Results: 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 weigth 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 aomunt 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).

Conclusion: 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.

Figure 1. The relationship between birth weight and fluid administration

^* The average amount of fluids given the first 10 days after birth.

Figure 2. The relationship between weight loss and fluid administration

Figure 3. The amounts of sodium given the first 10 days after birth.

Figure 4. The relationship between sodium administration and average sodium concentrations during the first 10 days after birth

* The amount of sodium given the first 10 days after birth.

Figure 5. The relationship between birth weight and sodium administration.

* The amounts of sodium given the first 10 days after birth.

Correspondence: Þórður Þórkelsson