How do osmotic diuretics reduce intracranial pressure?

• A. Increase cerebral blood flow
• B. Create osmotic gradient that draws water from brain to bloodstream
• C. Decrease systemic blood pressure
• D. Inhibit CSF production

Answer: (B)

Osmotic diuretics lower intracranial pressure by creating an osmotic gradient that pulls water out of brain tissue into the bloodstream. When given IV, these agents raise the osmolality of the plasma and stay largely in the vascular compartment because they don’t cross the blood–brain barrier easily. Water in brain cells and interstitial space moves toward the higher osmolality of the blood to rebalance the gradient, reducing brain edema and brain volume, which lowers ICP. This effect happens more from shifting water out of the brain than from changing CSF production or systemic blood pressure. After the initial osmotic pull, diuresis helps remove the excess fluid, but the key mechanism is the osmotic extraction of water from brain tissue. Monitor for dehydration, electrolyte shifts, and renal function during therapy.