Which type of dehydration is most commonly associated with acute gastroenteritis in children?

• A. Isotonic dehydration
• B. Hypotonic dehydration
• C. Hypertonic dehydration
• D. Dehydration with electrolyte imbalance

Answer: (A)

Isotonic dehydration is most common with acute gastroenteritis in children because the fluid lost through diarrhea and vomiting is similar in composition to plasma. When isotonic fluid is lost, extracellular fluid volume decreases but serum osmolality and sodium stay normal. This explains why these kids become volume-depleted without a rise or fall in plasma osmolality. If more electrolytes were lost than water, you’d get hypotonic dehydration with hyponatremia; if more water than electrolytes were lost, you’d get hypertonic dehydration with hypernatremia. A vague option like dehydration with electrolyte imbalance doesn’t capture the typical balanced loss seen in gastroenteritis.