BACKGROUND: A retrospective study was conducted in the Neonatal Intensive Care Unit of a tertiary hospital to determine the incidence of early hyponatraemia (first 48hours of life) in preterm infants. Risk and protection factors in this condition were also examined as a starting point for a change in the medical action when prescribing intravenous fluids.
METHODS: The study included a sample of 256 premature babies (gestational age: 235-366) admitted to the Neonatal Intensive Care Unit of a tertiary hospital between January 2016 and June 2018. The number of patients receiving intravenous sodium in different intervals during the first 48hours of life was determined, as well as the number of those with hyponatraemia of any type (<135mmol / l), and moderate-severe (<130mmol / l). An analysis was made of the relationship between early hyponatraemia and weight / gestational age, antenatal steroids exposure, respiratory pathology, early sepsis, and perinatal asphyxia.
RESULTS: Hyponatraemia occurred in 81 patients, 31.64% of the total (up to 50% in<30 weeks of gestational age), and was moderate-severe (<130mmol / l) in 17.3% of the cases. The period of time with the most cases of hyponatraemia was in the first 12hours of life (22.64%). Weight (P=.034), gestational age (P<.001) and respiratory disease (P<.001) were found to be risk factors and, in a multivariate analysis, the latter was independently related to early hyponatremia (P<.01, OR=5.24, 95% CI: 2.79-9.84). Antenatal betamethasone exposure did not show to be a protection factor.
CONCLUSIONS: According to the results of this study, it is considered an advantage to provide sodium in the intravenous fluids prescribed during the first days of life, particularly in preterm infants of lower gestational age and with respiratory disease involvement.

Urea has been recently proposed for the management of hyponatremia linked to the syndrome of inappropriate secretion of ADH (SIADH). The objective of the study was to review the levels of evidence for treatment of hyponatremia associated with SIADH with urea. We performed a: systematic review of experimental trials and grading according to SIGN. No clinical trials were found. The 6 studies analysed had methodological limitations and were prone to biases. In conclusion, there is no evidence to support the efficacy of urea for the treatment of hyponatremia following SIADH.