Why are mannitol or hypertonic saline used for raised ICP and what monitoring is essential?

• A. They increase brain water and raise ICP.
• B. They decrease brain water and lower ICP osmotically; monitor serum osmolality, electrolytes, urine output, and renal function.
• C. They treat infection.
• D. They provide analgesia.

Answer: (B)

These therapies work by creating an osmotic gradient that reduces brain water and lowers intracranial pressure. Mannitol and hypertonic saline raise the osmolality of the plasma, pulling water out of swollen brain tissue into the bloodstream, which decreases brain edema and helps restore cerebral perfusion.

Because this fluid shift and the high osmolar load can cause harm if not watched carefully, essential monitoring includes:

• Serum osmolality: to avoid excessive hyperosmolality that can risk cellular dehydration and kidney injury. The goal is to keep osmolality within a safe range, with adjustments based on response and protocol.

• Electrolytes, especially sodium: to detect shifts toward hypernatremia or hyponatremia. Rapid changes in sodium can worsen cerebral edema or cause other complications, so careful titration and monitoring are needed.

• Urine output: to assess the diuretic effect and fluid balance. High urine output may indicate effective diuresis, but it also raises the concern for volume depletion that could compromise cerebral perfusion.

• Renal function: to ensure the kidneys are clearing the osmotic agent adequately and to detect early signs of renal impairment that could necessitate therapy adjustments or avoidance of further osmotic load.

Ongoing clinical assessment and, when indicated, continued ICP monitoring help guide therapy and prevent complications while these agents are used.