Which statement about hypotonic fluids is true?

• A. They should be used with 3rd space shifts
• B. They are used to increase serum osmolality
• C. They should not be used with 3rd space shifts or intracranial pressure
• D. They are contraindicated in dehydration

Answer: (C)

Hypotonic fluids have a lower osmolality than plasma, so they draw water from the extracellular space into cells. That can cause cells to swell, including brain cells. If a patient already has third-space fluid shifts or increased intracranial pressure, giving hypotonic fluids can worsen edema and brain swelling. For that reason, they should not be used when third-space shifts or intracranial pressure are present.

In short, their effect is to decrease serum osmolality rather than increase it, and they’re not the go-to choice for dehydration because they won’t reliably restore circulating volume and can worsen edema or hyponatremia.