Which osmotic diuretic is commonly used to reduce intracranial pressure?

• A. Acetazolamide
• B. Mannitol
• C. Furosemide
• D. Hydrochlorothiazide

Answer: (B)

Osmotic diuretics reduce intracranial pressure by raising the osmolality of the blood, which pulls water out of swollen brain tissue into the bloodstream. Mannitol is the classic agent for this purpose because, when given intravenously, it is filtered by the kidneys but not reabsorbed. This keeps it in the plasma, increasing plasma osmolality and creating an osmotic gradient that draws water from brain parenchyma into the vascular space, thereby decreasing cerebral edema and lowering ICP quickly.

This makes mannitol particularly useful in acute settings such as head injury, intracranial hemorrhage, or other causes of cerebral edema where rapid ICP reduction is needed. It’s typically administered as an IV bolus with careful monitoring of fluid balance, electrolytes, and renal function. Be mindful of its risks: overdiuresis can lead to dehydration and electrolyte disturbances, and if the blood-brain barrier is severely disrupted, mannitol can be less predictable and may worsen edema or contribute to pulmonary edema.

Other diuretics behave differently and aren’t primarily used for acute ICP reduction. Acetazolamide can reduce CSF production but isn’t an osmotic agent; furosemide is a loop diuretic with indirect effects on ICP; hydrochlorothiazide is a thiazide diuretic with no primary role in acute ICP management.