Late hyponatremia in preterm infants

Influence of NaCl Supplementation on Vasopressin Secretion and Water Excretion in Premature Infants

“…The possible role of excess AVP and free water retention has also been claimed because during the course of late hyponatremia there has been a progres sive increase in daily AVP excretion [4]. Ex tracellular volume contraction due to primary sodium deficiency and decreased intravascu lar volume in association with hypoalbuminemia have been proposed as a stimulus for AVP release [4][5][6], In this regard, it is to be considered that although total body water and extracellular water estimates by Roy et al [3] indicate no difference in very low birth weight infants with or without hyponatremia, Shaffer et al [15] have demonstrated that infants de veloping late hyponatremia have significantly lower extracellular volume han infants who maintain normal serum sodium concentra tions. Data on AVP secretion in relation to sodium balance in premature infants are scanty.…”

“…In a previous study we have demonstrated simul taneous increase in urinary aldosterone and AVP excretion in association with progressive hyponatremia in a group of healthy prema ture infants. Protracted renal sodium loss has been claimed, therefore, to result in extracel lular volume contraction, stimulation of AVP secretion, enhancement of renal water reab sorption, and as a consequence in a fall in plasma sodium concentration [4], This con tention, however, has been challenged be cause hypoalbuminemia, frequently encoun tered in low birth weight neonates, has also been shown to produce hyponatremia through a reduction of the circulatory volume which may act as a stimulus for AVP excretion [5,6]. It is of further concern that in our study the urinary AVP excretion was not corrected for creatinine or glomerular filtration rate, thus its increasing daily excretion rate with age might reflect improving renal function rather than an increase in pituitary AVP secretion.…”