Developmental Study of the Renal Response to an Oral Salt Load in Preterm Infants

Aperia, A., Broherger, O., Thodenius, K. and Zetterström, R. (Department of Paediatrics, Karolinska Institutet, S:t Göran's Children's Hospital, Stockholm, Sweden). Developmental study of the renal response to an oral salt load in preterm infants. Acta Paediatr Scand 63: 517, 1974.—An evaluation of sodium homeostasis in 44 preterm infants with gestational ages between 29 and 37 weeks has been carried out during the first week after birth and until time of expected term. The natriuretic response to an oral sodium load has been studied in all infants and the GFR (single injection technique of inulin) in 17 infants. The results are compared with those previously found in full‐term infants. The natriuretic response was highest and the GFR was lowest in the very preterm neonates. In the very preterm infants the values for sodium excretion and GFR was just about the same at the time of expected term as in full‐term newborns. Various explanations for the difference between the very preterm neonates and full‐term neonates are discussed. One factor of importance might he the anatomical development. The immature kidney has in comparison to the adult kidney relatively larger glomerular than tubular mass. Extra‐uterine life seems to have little influence on the development of GFR as well as on the development of the response to the oral salt load. Thus in the very preterm infants, the postmenstrual rather than the postnatal age should be considered when prescribing fluid, electrolytes and drugs.