Holliday et al suggested that rehydration in hypovolaemic children with acute gastroenteritis should be by rapid infusion of isotonic saline.¹ The authors refer to studies demonstrating a faster return of antidiuretic hormone (ADH) levels to normal as a marker for the restoration of intravascular volume in children receiving rapid intravascular volume expansion. The authors also mention that ADH secretion in children with gastroenteritis is stimulated by nausea and vomiting. Nausea and vomiting is fuelled by starvation ketosis² in dehydrated children with gastroenteritis. In addition to gastroenteritis induced acidosis, the rapid application of isotonic saline also predictably causes significant hyperchloraemic acidosis by reducing the strong anion gap.³ Induction of hyperchloraemic acidosis has been demonstrated in double-blind randomised controlled trials of patients receiving rapid isotonic saline infusions as volume replacement therapy during operations in theatre.⁴ The resulting hyperchloraemic acidosis can reduce gastric perfusion and the glomerular filtration rate,⁵ and prompt the administration of unnecessary additional fluid boluses by physicians who may think the metabolic acidosis is caused by hypovolaemia. Isotonic saline infusion is also unable to switch off ketogenesis, leaving the patient exposed to nauseating amounts of ketone bodies. Glucose application is essential to reduce ketone bodies by stimulating insulin secretion and thus switching off ketogenesis.⁶ The authors also seem to advocate …