Balanced Crystalloid vs Normal Saline in Pediatric Acute Gastroenteritis

Acute gastroenteritis (AGE) is among the most common reasons for paediatric emergency visits. Children with significant dehydration often require intravenous (IV) fluid therapy. Two main types of IV crystalloid solutions are currently used in clinical practice: 0.9% sodium chloride (normal saline, NS) and balanced crystalloids such as Isolyte-S, which contain acetate and gluconate as bicarbonate precursors. Normal saline has a high chloride content (154 mEq/L), which may worsen the metabolic acidosis already present in many children with acute gastroenteritis. Balanced crystalloids have a chloride content closer to that of plasma (98 mEq/L) and additionally contain acetate and gluconate, which are metabolised in peripheral tissues to consume hydrogen ions and thereby raise serum bicarbonate - a mechanism distinct from simply avoiding chloride overload. This study prospectively observes and compares early biochemical and clinical outcomes in children with acute gastroenteritis who receive one of these two fluid types as part of their routine clinical care. The treating physician independently decides which fluid to use; the research team does not influence this decision and does not order any additional tests or procedures. Laboratory values used as outcomes are drawn solely from blood tests obtained as part of standard care. The primary aim is to determine whether, at approximately 4 hours after IV fluid start, serum bicarbonate has changed more in children who received a balanced crystalloid compared with those who received normal saline. Secondary aims include comparing blood pH, chloride levels, need for additional IV boluses, time to first oral fluid intake, hospitalisation rate, and 72-hour return visits.