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Fluid and electrolyte therapy in newborns

Jochen Profit, MD, MPH
Section Editors
Steven A Abrams, MD
Kathleen J Motil, MD, PhD
Deputy Editor
Melanie S Kim, MD


Water and electrolyte homeostasis in newborn infants is influenced by physiologic adaptations following birth, and developmental effects on the distribution of total body water and water loss. Fluid and electrolyte therapy must account for these factors in determining maintenance requirements and correction of any abnormalities.


Total body water is composed of extracellular fluid (ECF), which includes intravascular and interstitial fluid, and intracellular fluid. The distribution between these compartments changes with increasing gestational age [1]. Compared with an infant born at 27 weeks, a newborn term infant has a total body water that comprises a smaller fraction of body weight (75 versus 80 percent) and an ECF volume that is a smaller fraction of total body water (45 versus 70 percent) [2].

Infants normally lose weight during the first week after birth. This weight loss is greater in preterm than term infants (approximately 10 to 15 versus 5 percent) and is associated with a diuresis. The postnatal diuresis is approximately 1 to 3 mL/kg per hour in term infants and is greater in preterm infants. Physiologic weight loss results primarily from an isotonic reduction in extracellular water, although the mechanism for this process is uncertain [1].


Water loss can occur through the kidneys, skin, and lungs. The absolute and relative amounts of water loss through these routes change with development. Excessive loss of other fluids, such as stool, gastric drainage, or thoracostomy output, can lead to water and electrolyte disturbances.

Renal — A urine volume of approximately 45 mL/kg per day, or 2 mL/kg per hour, allows excretion of a normal solute load, typically in a dilute urine. Changes in urinary water and electrolytes occur with changes in blood flow and maturation of renal function. The proportion of cardiac output directed to the kidneys increases during gestation and after birth. This proportion is 2 percent during the first week after birth at term, 8.8 percent at five weeks of age, and 9.6 percent at one year [3]. In contrast, approximately 16 percent of cardiac output in adults goes to the kidneys [4].

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Literature review current through: Nov 2017. | This topic last updated: Jun 04, 2014.
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