Increased extracellular water with decreased serum sodium in newborns after CNS trauma is associated with SIADH. What is the recommended treatment?

• A. Free water restriction
• B. Increase free water intake
• C. Hypertonic saline administration
• D. Isotonic saline administration

Answer: (C)

In SIADH, excess ADH causes water retention, leading to increased extracellular water with dilutional hyponatremia. In a newborn with CNS trauma, this hyponatremia can worsen brain edema and neurologic injury, so treatment focuses on safely raising the serum sodium to reduce cerebral edema. Hypertonic saline increases plasma osmolality, draws water out of swollen brain cells, and rapidly corrects the hyponatremia. This makes it the most appropriate choice for a symptomatic neonate with SIADH after CNS injury. Free water restriction alone may not be enough for acute hyponatremia, and increasing free water would worsen the condition; isotonic saline often doesn’t correct the hyponatremia in SIADH and can perpetuate water retention. Monitor correction closely to avoid rapid overcorrection and osmotic injury.