Explanation

Mannitol is an osmotic diuretic used to reduce increased intracranial pressure. It works by increasing the osmolality of the blood, drawing fluid from the interstitial spaces (including brain tissue) into the intravascular space. This excess fluid is then filtered by the kidneys and excreted as urine. Therefore, a significant increase in urine output (diuresis) is the expected and desired therapeutic effect, indicating that fluid is being effectively removed from the body, which helps to lower ICP.

A decreased level of consciousness or pupils becoming fixed and dilated would indicate worsening ICP, not improvement. Hypotension (BP 90/50 mmHg) can be an adverse effect of mannitol due to excessive fluid removal (dehydration) but is not the desired therapeutic effect related to ICP reduction.