Hypernatremia in an elderly patient with low water intake is best treated by:

• A. Isotonic saline
• B. Rapid correction with hypertonic saline
• C. Slow correction with hypotonic saline or 0.45% saline
• D. Fluid restriction

Answer: (C)

When hypernatremia is due to a water deficit, the goal is to replace free water slowly to bring the serum sodium down gradually without causing osmotic injury to brain cells. In elderly patients with low water intake, hypernatremia is often chronic, and the brain has adapted by accumulating osmolytes. If we correct too quickly, water rushes into brain cells and can cause cerebral edema. Therefore, the safest and most effective approach is to provide free water slowly through hypotonic fluids, such as 0.45% saline or dextrose-containing solutions that are effectively hypotonic relative to plasma. The correction should be gradual, aiming to lower the sodium by about 0.5 mEq/L per hour or roughly 10–12 mEq/L over 24 hours, with close monitoring of serum Na and osmolality.

Isotonic saline would help replenish volume but does not address the free-water deficit and can maintain or worsen the hypernatremia if used alone. Rapid correction with hypertonic saline would raise the serum sodium further and is not appropriate. Fluid restriction would worsen the hypernatremia by limiting water intake.