Choong et al, conducted a randomized controlled study involving 258 patients aged 6 months to 16 yrs of age with expected postoperative stay of >24hrs. Patients with uncorrected plasma sodium level, abnormal ADH secretion, recent diuretic use, on total parenteral nutrition were excluded from study. Patients were randomized into hypotonic perioperative maintainence solution(PMS) (n=130) or isotonic PMS (n=128) group by a computer generated randomization sequence. The primary outcome was hyponatremia occurring during study intervention and secondary outcomes were severe hyponatremia, hypernatremia, and plasma ADH levels. This study showed that the risk of hyponatremia was greater for patients who received hypotonic PMS, compared with isotonic PMS (40.8% vs 22.7%; RR: 1.82 [95% CI: 1.21-2.74]; P=0.004). Eight patients (6.2%) developed severe hyponatremia following hypotonic PMS, compared with 1 patient (0.8%) in the isotonic PMS group (RR: 7.21 [95% CI:0.93-55.83]; P =0.059). The risk of hypernatremia was not significantly different between the 2 groups.