Plasma electrolytes in the neonatal period.

Summary 1. The plasma Na, K, CI and CO2 levels were determined in 32 full-term and 30 premature infants, from the 1st to the 7th day inclusive. 2. The full-term infants showed on the first day a slight acidosis which disappeared gradually in a few days. The other values were the same as in adults. 3. The premature infants showed a normal Na and a slightly high K content, but they had a distinct hyperchloraemic acidosis, which remained stationary during the first week. 4. The acidosis on the first day is ascribed to residual effects of an anaerobic metabolism in utero or during birth. The hyperchloraemic acidosis of the premature infants is ascribed to the physiological immaturity of the kidney with respect to the chloride clearance. 5. The electrolyte values in premature infants showed a large dispersion, which points to the lability of the premature infant in maintaining the equilibrium of plasma electrolytes.