Aims:To determine whether the risk of hyponatraemia in children with gastroenteritis receiving intravenous(IV)fluids is decreased by the use of 0.9%saline.Methods:A prospective randomised study was carried out in a tertiary paediatric hospital.A total of 102 children with gastroenteritis were randomised to receive either 0.9%saline +2.5%dextrose(NS)or 0.45%saline +2.5%dextrose(N/2)at a rate determined by their treating physician according to hospital guidelines and clinical judgement.Plasma electrolytes,osmolality,and plasma glucose were measured before(T0)and 4 hours after(T4)starting IV fluids,and subsequently if clinically indicated.Electrolytes and osmolality were measured in urine samples.Results were analysed according to whether children were hyponatraemic(plasma sodium < 135 mmol/l)or normonatraemic at T0.Results:At T0,mean(SD)plasma sodium was 135(3.3)mmol/l(range 124-142),with 37/102(36%)hyponatraemic.At T4,mean plasma sodium in children receiving N/2 remained unchanged in those initially hyponatraemic(n = 16),but fell 2.3(2.2)mmol/l in the normonatraemic group.In contrast,among children receiving NS,mean plasma sodium was 2.4(2.0)-mmol/l higher in those hyponatraemic at baseline(n = 21)and unchanged in the initially normonatraemic children.In 16 children who were still receiving IV fluids at 24 hours,3/8 receiving N/2 were hyponatraemic compared with 0/8 receiving NS.No child became hypernatraemic.Conclusions:In gastroenteritis treated with intravenous fluids,normal saline is preferable to hypotonic saline because it protects against hyponatraemia without causing hypernatraemia. Aims: To determine whether the risk of hyponatraemia in children with gastroenteritis receiving intravenous (IV) fluids is decreased by the use of 0.9% saline. Methods: A prospective randomized study was carried out in a tertiary pediatric hospital. A total of 102 children with 0.9% saline + 2.5% dextrose (NS) or 0.45% saline + 2.5% dextrose (N / 2) at a rate determined by their treating physician according to hospital guidelines and clinical judgment. Plasm electrolytes, osmolality, and plasma glucose were measured before (T0) and 4 hours after (T4) starting IV fluids, and if if clinically indicated. Electrolytes and osmolality were measured in urine samples. Results were analyzed according to whether children were hyponatraemic (plasma sodium <135 mmol / l) or normonatraemic at T0. Results: At T0, mean (SD) plasma sodium was 135 (3.3) mmol / l range 124-142, with 37/102 (36%) hyponatraemic. in children receiving N / 2 remained unchanged in th In pink and hyponatraemic groups (n = 16), but fell 2.3 (2.2) mmol / l in the normonatraemic group. In contrast, among children receiving NS, mean plasma sodium was 2.4 (2.0) -mmol / l higher in those hyponatraemic at baseline n = 21) and unchanged in the initially normonatraemic children. In 16 children who were still receiving IV fluids at 24 hours, 3/8 receiving N / 2 were hyponatraemic compared with 0/8 receiving NS. No child became hypernatraemic. Conclusions: In gastroenteritis treated with intravenous fluids, normal saline is preferable to hypotonic saline because it protects against hyponatraemia without causing hypernatraemia.