Fecal sodium and potassium losses in low brith weight infants

We measured 24-hour fecal losses of sodium (Na) and potassium (K) in immediate post natal period of preterm neonates to determine the role of this route in the electrolyte imbalances seen in such infants. The values from preterm infants were compared to a group of age matched term infants. Eleven studies were done on unfed extremely low birth weight infants (group I, birth weight <1200 gms), seven on fed preterm infants (group II, birth weight 1201–2500 gms) and nine on fed term infants (group III, birth weight 2501–4000 gms). Measured and derived variables compared between the groups were 24 hour fecal volume, total fecal electrolyte contents, Na or K lost per kg of body weight and per gm of stool and Na or K losses as percent of intake. Although 24 hour fecal volume was lowest in group I, none of the variables related to Na differed between groups I and II whereas all of them were significantly lower in group I when compared with group III. Groups II and III differed only in terms of Na loss/gm stool which was lower in the previous group. Conversely K loss/gm of stool was significantly higher in group I when compared with both groups II and III and the only variable that differed between groups II and III was a higher fecal K content as fraction of intake. Fecal K/Na ratio was highest in group I, and decreased progressively with advancing gestational age, whereas creatinine clearance was lowest in group I and increased along with gestational age. Serum electrolyte levels were normal, although serum Na concentration was lowest in group I and serum K concentration highest in group II. We conclude that very low birth weight infants have relatively higher fecal K concentrations in the first week of extrauterine life, and speculate that this might have physiological significance as these infants are prone to hyperkalemia during this period.