Acid-base homeostasis of low-birth-weight and full-term infants in early life.

Renal tubular function tests on hydrogen ion excretion capacity and concentration capacity performed during the first month of life show that these functions are not fully developed although they may be adequate for the needs of the breastfed infant. A positive net acid balance due to a less well-developed renal acidifying capacity is a fairly common situation during the first weeks of life. Late metabolic acidosis could thus be demonstrated in a frequency of up to 20% in preterm babies depending on the quantity as well as the quality of the dietary protein; the corresponding figure in term babies was about 5%. Furthermore, it must be taken into account that the elimination of one metabolite may affect the efficiency of other excretory mechanisms. It could thus be shown that during an acid loading period, the maximum renal concentration capacity falls from preloading values of 500-600 to 300-400 mOsm/1. When a pitressin load was superimposed on an acidification test, the net acid excretion was reduced, especially in infants on a high protein intake. Therefore, if in the immature infant the composition of dietary intake is inappropriate as to the protein intake and/or solute load, the limit of capacity of certain renal tubular functions may be exceeded, especially under conditions of stress, and this could result in homeostatic disturbances, i.a. of the acid-base balance.