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1612 FRACTIONAL EXCRETION OF SODIUM IN LOW BIRTH WEIGHT INFANTS

The small premature infant is at risk of developing renal impairment. The fractional excretion of sodium (FeNa) has proven useful to define renal tubular integrity. The FeNa is inversely proportional to gestational age, but little information is available about the FeNa in birth weight <1500 grams. We studied 36 unselected consecutive newborns of this size longitudinally over the first 21 days of life. For our group, mean birthweight was 1173 +/- 206 gm., gestational age was 29.4 +/- 2.4 weeks, and apgars were 4.8 +/- 2.7 at one minute, and 6.9 +/- 2.1 at 5 minutes. A total of 125 determinations of FeNa were made.Thus, the FeNa decreases over the first 21 days of life with mean less than 3 by 21 days. The creatinine also decreases over this time interval. Infants with abnormal urinalysis have higher FeNa's than those with normal urinalysis. We conclude that these values will be helpful in interpreting FeNa's and degree of tubular damage in premature infants.