Mannitol has a long history of use to decrease intracranial pressure in neurosurgery and traumatic brain injury but it’s effect on long term outcome is still uncertain.
This free full text review – a meta-analysis and systematic review – surveys its history and usage. Its conclusion is essentially:
“Mannitol is effective in accomplishing short-term clinical goals, although hypertonic saline is associated with improved brain relaxation during craniotomy. Mannitol has a favorable safety profile although it can cause electrolyte abnormality and renal impairment. More research is needed to determine its impacts on long-term outcomes.”