Usefulness of fractional excretion of sodium in critically ill pre-term newborns.

The purpose of this prospective study was to measure the fractional excretion of sodium (FENa) in critically ill pre-term newborns (PTNB) in order to determine its cut point in the diagnosis of acute renal failure (ARF). This study included 52 newborns and was conducted from May, 1994 to May, 1995. Patients were divided in two groups: patients without ARF in group A (n = 47) and patients with ARF in group B (n = 5). No statistically significant differences were found in birth weight, extrauterine life span, serum sodium levels, urine creatinine and urinary volumes between the two groups, but there was a difference in gestational age, urinary sodium concentration and serum creatinine levels. Sensitivity and specificity were determined, and the critical level of FENa was 4% or greater for ARF diagnosis. The average FENa value for Group A was 1.4 +/- 1.4% with a median of 0.92%. In Group B, average FENa was 6.9 +/- 2.9% with a median of 8.5% (P < 0.001). We conclude that FENa is a valuable tool for the assessment of renal function in critically-ill PTNB, in spite of all other factors present in this population that could modify its values.