Salt and fluid balance in newborn infants.

About 5 years ago it was widely thought that preterm infants should be supplemented with extra sodium to avoid hyponatremia. It has, however, to be pointed out that VLBW infants during the first postnatal week run a risk of developing hypernatremia which makes it difficult to give general recommendations for sodium supplementation. Since the serum sodium level depends not only upon the balance between sodium intake and sodium excretion but also upon the water balance which may vary depending on the clinical condition of the baby, it seems advisable to monitor the serum sodium level in all preterm infants. Supplementation should be given in case of hyponatremia. In instances of hyponatremia it also has to be considered if the infant due to positive fluid balance has retained fluid in excess of sodium. As a general conclusion the importance of monitoring sodium balance in every preterm infant should be stressed. Disturbances are most likely to occur in VLBW infants and in infants with acute illnesses. The best way of assisting fluid balance is by repeated accurate measurements of the body weight. It should, however, be kept in ming that no reliable methods are available for the measurement of the body weight of a preterm infant who is under intensive care and who cannot be taken out of the incubator. Serum sodium levels may give information of the sodium balance but it has to be stressed that fluid and sodium balances are always interrelated and that it is desirable to have simultaneous estimations of both balances. Excess retention of fluid may be caused primarily by excess retention of sodium or by fluid.(ABSTRACT TRUNCATED AT 250 WORDS)