Regulation of serum sodium in dehydrated and orally rehydrated infants. Influence of age and of purging rates.

We have examined the control of serum sodium concentration (S-Na) in 60 male infants with acute diarrheal disease, moderate dehydration, but without the presence of fever, vomiting or other conditions. The infants were studied on admission and during oral rehydration therapy (ORT). We examined the effect of rapid reduction of the purging rate on the control of S-Na by adding pulverized rice and pulses (dal moong) to the rehydration solution. On admission S-Na was significantly inversely related to age. This correlation could not only be attributed to difference in stool sodium losses. Changes in S-Na and urinary K/Na ratio during oral rehydration therapy (ORT), were analyzed separately in infants below and above 4 month of age. During the first six hours of ORT, there was an increase in S-Na in all groups. During the following 18 hours, S-Na tended to normalize around 138 mmol/l. Normalization occurred faster if purging rate was reduced. In all groups urinary K/Na ratio (index of aldosterone production and, inversely, of sodium balance), was high at admission and fell during ORT. In the youngest infants (below 4 month of age) the fall was significantly more pronounced if the purging was reduced. We conclude that it is important to consider age when prescribing ORT. The capacity to correct disturbances in S-Na becomes more efficient during maintenance stage of ORT. Correction of S-Na and sodium balance is enhanced by rapid reduction of abnormal intestinal losses.