Sodium supply influences plasma sodium concentration and the risks of hyper- and hyponatremia in extremely preterm infants

Pediatr Res. 2017 Mar;81(3):455-460. doi: 10.1038/pr.2016.264. Epub 2016 Dec 9.


Background: Hyper- and hyponatremia occur frequently in extremely preterm infants. Our purpose was to investigate plasma sodium (P-Na) concentrations, the incidence of hyper- and hyponatremia, and the impact of possible predisposing factors in extremely preterm infants.

Methods: In this observational study, we analyzed data from the EXtremely PREterm (< 27 wk.) infants in Sweden Study (EXPRESS, n = 707). Detailed nutritional, laboratory, and weight data were collected retrospectively from patient records.

Results: Mean ± SD P-Na increased from 135.5 ± 3.0 at birth to 144.3 ± 6.1 mmol/l at a postnatal age of 3 d and decreased thereafter. Fifty percent of infants had hypernatremia (P-Na > 145 mmol/l) during the first week of life while 79% displayed hyponatremia (P-Na < 135 mmol/l) during week 2. Initially, the main sodium sources were blood products and saline injections/infusions, gradually shifting to parenteral and enteral nutrition towards the end of the first week. The major determinant of P-Na and the risks of hyper- and hyponatremia was sodium supply. Fluid volume provision was associated with postnatal weight change but not with P-Na.

Conclusion: The supply of sodium, rather than fluid volume, is the major factor determining P-Na concentrations and the risks of hyper- and hyponatremia.

Publication types

  • Observational Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Body Weight
  • Enteral Nutrition
  • Female
  • Humans
  • Hypernatremia / blood*
  • Hyponatremia / blood*
  • Infant, Extremely Premature
  • Male
  • Parenteral Nutrition
  • Prospective Studies
  • Risk Factors
  • Sodium / blood*
  • Sodium Chloride
  • Sweden
  • Time Factors


  • Sodium Chloride
  • Sodium