Isotonic dehydration pattern described by?

• A. More water loss than electrolytes.
• B. Water loss only.
• C. Near normal serum sodium with equal loss of water and electrolytes.
• D. Electrolyte loss without water loss.

Answer: (C)

Isotonic dehydration occurs when water and electrolytes are lost in roughly equal amounts, so the serum sodium stays near normal and the osmolar balance is preserved. This pattern is common with acute diarrheal illnesses where both fluid and electrolyte losses occur together, leading to reduced extracellular fluid volume without a change in serum sodium. Therefore, the description of near normal serum sodium with equal loss of water and electrolytes best fits isotonic dehydration. If more water than electrolytes were lost, you'd see hypernatremia (hypertonic dehydration); if electrolytes were lost without proportionate water loss, the electrolyte balance would shift and serum sodium would not remain normal; water loss without electrolyte loss would also disrupt osmolality. Management focuses on restoring intravascular volume with isotonic fluids, such as normal saline.