In acute diarrheal dehydration in children, which of the following best describes the pathophysiology of hyponatremic dehydration?

Explanation

## Pathophysiology of Hyponatremic Dehydration **Key Point:** Hyponatremic dehydration occurs when sodium losses exceed water losses, leading to a serum sodium concentration <130 mEq/L. This is the most common type of dehydration in acute diarrhea in children. ### Mechanism In acute diarrhea: - Both sodium and water are lost in stool - If sodium loss is disproportionately greater than water loss, the serum osmolality decreases - This causes water to shift intracellularly, leading to cellular edema - Hyponatremia develops (serum Na⁺ <130 mEq/L) ### Clinical Significance | Type | Serum Na⁺ | Mechanism | Risk | |------|-----------|-----------|------| | **Hyponatremic** | <130 mEq/L | Na⁺ loss > H₂O loss | Cerebral edema, seizures | | **Isonatremic** | 130–150 mEq/L | Proportional loss | Most common, safest | | **Hypernatremic** | >150 mEq/L | H₂O loss > Na⁺ loss | Cellular dehydration, hyperglycemia-like state | **High-Yield:** Hyponatremic dehydration is the most dangerous type because it predisposes to cerebral edema and seizures. Rapid correction is contraindicated — sodium must be corrected slowly (no more than 10–12 mEq/L per 24 hours) to avoid osmotic demyelination. **Clinical Pearl:** Hyponatremic dehydration is more common in children who have been given hypotonic fluids (e.g., plain water, dilute dextrose) or in those with excessive insensible losses and inadequate sodium intake.