Dehydration in pediatric surgical patients is almost always hypotonic. When rehydrating, it is important to replenish both fluid and sodium. Hypotonic dehydration in pediatric surgical patients is often corrected with isotonic solutions, commonly using normal saline or 2:1 solution. The initial infusion rate is 20 ml/kg, administered rapidly over 0.5 to 1 hour, and can be repeated if necessary. Subsequently, fluids should be administered at 8~10 ml/kg/h, ideally completing rehydration within 8~12 hours.