Osmotherapy in TBI reduces intracranial pressure by:

• A. Creating an osmotic gradient to draw fluid from brain tissue into the vasculature
• B. Increasing cerebral blood flow by vasodilation
• C. Decreasing CSF production by choroid plexus suppression
• D. Enhancing neuronal excitability

Answer: (A)

Osmotherapy lowers intracranial pressure by creating an osmotic gradient that pulls water out of swollen brain tissue into the bloodstream. In moderate to severe TBI, brain edema increases intracranial pressure and compromises perfusion. Administering a hyperosmolar solution (like mannitol or hypertonic saline) raises the osmolality of the plasma relative to the brain interstitial fluid. This osmotic difference causes water to move from the brain parenchyma into the intravascular space, reducing brain water content and volume, which lowers ICP. Hyperosmolar therapy can also improve cerebral perfusion pressure by expanding intravascular volume (especially with hypertonic saline), but the primary effect is drawing edema fluid out of the brain.

Context helps: this is a rapid, temporizing measure for raised ICP; its effect is not permanent and requires careful monitoring of serum osmolality, electrolytes, and volume status to avoid complications such as hyponatremia, hypernatremia, dehydration, or renal issues.

Other mechanisms listed don’t target edema relief in the brain the same way: increasing cerebral blood flow by vasodilation can raise, not lower, ICP due to increased cerebral blood volume; decreasing CSF production via choroid plexus suppression is not how osmotherapy works; and enhancing neuronal excitability would worsen injury and ICP.