Fractional Excretion And Reabsorption Of Sodium In Clinically Stable Nigerian Newborn O. T. Adedoyin, J. A. Olowu, O. A. Ajayi, A. B. Okesina

SUMMARY

Background: There is no study known on fractional reabsorption and excretion of sodium in the newborns in the tropics inspite of the fact that sodium-containing fluids are commonly administered to these babies when they require parenteral fluids. To prevent sodium deficits or overload in these babies, a local knowledge of the capacity of the neonatal kidney to reabsorb and excrete sodium is essential.

Objective: To determine the fractional reabsorption and excretion of sodium in clinically stable normal newborns of different gestational ages seen at the University of Ilorin Teaching Hospital, Ilorin, Nigeria.

Materials and methods: The fractional excretion of sodium of 80 clinically stable (appropriate for gestational age) newborns of different gestational ages (comprising 60 preterm and 20 term babies) were determined using a standard formula. The fractional reabsorption of sodium was derived from the fractional excretion of sodium thus: (100% - fractional excretion of sodium in %).

Results: The mean fractional excretion of sodium in preterm babies (n=60) was 2.1% as against 0.4% in term babies (n=20), while the mean fractional reabsorption of sodium in preterm babies was 97.9% as against 99.6% in term babies (P<0.05).

Conclusion: The fractional reabsorption of sodium becomes more efficient as the gestational age increases, resulting in the reduction of the fractional excretion of sodium. Regular monitoring of the serum sodium in preterm babies is therefore necessary because the increased fractional excretion may result in significant hyponatraemia which may need correction. Niger Med J. 2003; Vol 44 (3):64 - 67.

KEYWORDS: Fractional excretion; Fractional reabsorption; Sodium; Newborn.