Risk Factors for Late-onset Hyponatremia and Its Influence on Neonatal Outcomes in Preterm Infants

Abstract

Late-onset hyponatremia (LOH), hyponatremia occurring after two weeks of age with the achievement of full feeding, is the result of a negative sodium balance caused by inadequate salt intake or excessive salt loss due to immature renal or intestinal function in preterm infants. The aims of our study were to identify the risk factors for LOH and its influence on neonatal outcomes. This was a retrospective cohort analysis of 161 preterm infants born before 34 weeks of gestation between June 2009 and December 2010 at Seoul National University Hospital. LOH was defined as a sodium level ≤ 132 mEq/L or 133-135 mEq/L with oral sodium supplementation. LOH occurred in 49 (30.4%) of the studied infants. A lower gestational age, a shorter duration of parenteral nutrition, the presence of respiratory distress syndrome, the use of furosemide, and feeding with breast milk were significant risk factors for LOH. In terms of neonatal outcomes, the infants with LOH had longer hospital stays and higher risks of bronchopulmonary dysplasia and retinopathy of prematurity requiring surgery. LOH lasting at least 7 days significantly increased moderate to severe bronchopulmonary dysplasia, periventricular leukomalacia, and extra-uterine growth retardation. LOH is commonly observed in preterm infants; it may be a risk factor for bronchopulmonary dysplasia and retinopathy of prematurity or a marker of illness severity.

Risk Factors and Effects of Severe Late-Onset Hyponatremia on Long-Term Growth of Prematurely Born Infants

“…3 ). A causal relationship between sodium deficiency and impaired growth was suggested previously [ 11 ], and LOH of premature infants could reportedly influence extrauterine growth retardation [ 4 ]. In previous reports, the duration of hyponatremia could impair growth during the neonatal period, and delayed supplementation of sodium could partially restore growth.…”

“…The incidence of LOH is reportedly 20% and 30.4% despite the definitions of hyponatremia and inclusion criteria differing in previous studies [ 4 8 ]. In this study, the incidence of LOH was 30.0% among premature infants born at ≤32 weeks of gestation under the definition of hyponatremia of a serum sodium level <135 mEq/L.…”

“…A lower GA was considered a risk factor of LOH [ 3 4 ]. In this study, GA affected hyponatremia severity among premature infants with LOH ( Table 2 ).…”

“…BM feeding is a reported risk factor for LOH in premature infants, and the use of human milk fortifier and its increased sodium content were suggested as well [ 4 5 ]. However, the rates of BM feeding were not significantly different between patients with and those without LOH among the 340 premature infants (74.7% vs. 82.5%, p =0.122) and were not significantly different between the severe and mild LOH groups in this study (66.7% in both groups, Table 1 ).…”

“…LOH in premature infants is usually caused by inadequate sodium intake and renal salt wasting [ 1 2 ]. Although differentiating between early- and LOH in premature infants may be less relevant because individual neonatal clinical conditions are so diverse, neonatologists often experience LOH in relatively stable prematurely born infants, especially those with a lower gestational age (GA) [ 3 4 5 ].…”