In a patient with cerebral edema and hyponatremia, why is administering simple glucose (D5W) alone not adequate for nutrition?

• A. It provides insufficient calories.
• B. It lowers serum osmolality, increasing cerebral edema.
• C. It raises serum osmolality.
• D. It corrects hyponatremia.

Answer: (B)

In cerebral edema with hyponatremia, serum osmolality is the key factor controlling water movement between compartments. Water shifts toward lower osmolality, so lowering serum osmolality worsens brain swelling. Simple glucose (D5W) provides calories, but once the dextrose is metabolized, what remains is free water. This free water dilutes the serum, lowers osmolality further, and can raise water influx into brain cells, intensifying cerebral edema and worsening hyponatremia. So, while it supplies calories, it does not maintain or raise the necessary osmolality and thus is not adequate for nutrition in this context. In such patients, nutrition should be provided with solutions that preserve or increase serum osmolality and include electrolytes, or via appropriate nutrition support (balanced IV fluids or parenteral/enteral nutrition) with careful electrolyte management.