These effects facilitate the surgical approach to deep-lying structures of cranial cavity. Intraoperatively, mannitol is administered in dose ranges of 0.25~1g/kg. The administration of mannitol may cause adverse effects. such as; rebound of intracranial pressure, transient increases in circulating blood volume, increased serum osmolality and decreased serum electrolytes.

This study examined the influence of 20% mannitol on serum osmolality and electrolytes in 24 patients undergoing brain tumor, cerebral aneurysm and intracerebral hemmorrhage surgery. Measurement were made before the infusion of mannitol. 15 minutes following infusion. after dural closure and in the ICU.

There was a significant increase in serum osmolalitv after infusion of mannitol.

There was a significant decrease .in serum Na⁺ only 15 minutes following infusion. There was a significant decrease in serum K⁺ 15 minutes postinfusion and dural closure.

In conclusion, it is important to measure osmolality and electrolytes before and after infusion and adjust fluid administration.