The postoperative response of the term and preterm newborn infant to sodium administration

Twenty surgical newborn infants aged less than 5 days were selected for study to determine the quantity of sodium administered during operation and the subsequent 48 hours, and to determine their response to this sodium load. There were 6 preterm infants with gestational age 35 weeks or less and 14 full-term infants aged more than 35 weeks. Measurements calculated at 12 hourly intervals for 48 hours after operation included sodium intake, sodium excretion, fractional excretion of sodium, and serum sodium. No special guidelines were utilized for fluid management. The mean sodium intake during the 48-hour study period for the term infants was 15.7 mEq/kg, of which 46% was given during the first 12 hours, and for the premature infants was 17.1 mEq/kg, of which 56% was given during the first 12 hours. In the two groups of patients, the amount of sodium given during the first 12 hours was 470% and 480% of their estimated maintenance requirements, respectively. The mean sodium output during the first 12 hours was low in the term group (1.2 mEq/L) and the premature group (1.3 mEq/L), and subsequently increased reaching maximum levels of 2.3 and 2.1 mEq/L, respectively, by 36 hours. The fractional excretion of sodium exceeded 1.0% in 53% of the term and 94% of the preterm infants. During the study period, the mean serum sodium levels exceeded 145 mEq/L (hypernatremia) in 64% of the term and 67% of the preterm infants.(ABSTRACT TRUNCATED AT 250 WORDS)