[Developmental physiologic aspects of volume and sodium regulation in premature and mature newborn infants].

Concentrations of sodium and creatinine were measured in serum and time collected urine samples of 72 newborn infants in the first ten days of life. Creatinine clearances, fractional and absolute sodium excretions were calculated. For analysis the group of newborns was divided into three according to gestational age: group A: less than 33 weeks; group B: 33-37 weeks; group C: greater than 37 weeks. The GFR was correlated to the conceptional age. Renal sodium losses exceeded alimentary supplementation in premature infants during the observation period. An additional supplementation of sodium seems therefore to be indicated early in life, as sodium balance is negative from the first day on. Individual investigations are necessary to evaluate the amount of sodium needed. 3-5 mMol/kg/day seem to be well tolerated and preventive for hyponatriaemia. Fluid administration during the first days should be calculated so that a weight loss of about 10% of body weight is achieved in premature infants in order to prevent cardiovascular and gastrointestinal complications. Because of a higher insensible water loss the amount of fluids administered per body weight should be higher in prematures than in matures.