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[Correspondence] Isotonic fluid for intravenous hydration maintenance in children

The findings of the study by Sarah McNab and colleagues (March 28, p 1190)1 showed a substantial effect of isotonic fluid maintenance in children admitted to hospital. In the study, the number of patients who received emergency surgery between the two study groups, isotonic hydration with 140 mmol/L of sodium and hypotonic hydration with 77 mm/L of sodium, was significantly different (67 [20%] of 338 patients in the isotonic group vs 92 [27%] of 338 patients in the hypotonic group, p=0·02). I believe that this difference might have caused the difference in the number of patients with hyponatraemia because of the following reasons: the release of antidiuretic hormone is stimulated by surgical stress (eg, pain, narcotic use, and blood loss), which is experienced by many children undergoing surgery;2 previous studies3,4 suggest that the presence of hypotonic intravenous fluid during the perioperative period is associated with an increased risk of hyponatraemia; and the results of McNab’s study suggest that the risk of hyponatraemia might be greatest in the first 6 h of the study period in both treatment groups.