Additional therapy for increased ICP includes the use of osmotic diuretics, such as mannitol. In the face of deepening coma, pupil inequality, or other deterioration of the neurologic examination, mannitol may be life saving. Mannitol (0.25 to 1.0 gm/kg) can effectively reduce cerebral edema by producing an osmotic gradient that prevents the movement of water from the vascular space into the cells during membrane pump failure and draws tissue water into the vascular space. In effect, this reduces brain volume and provides increased space for an expanding hematoma or brain swelling. The osmotic effects of mannitol occur within minutes of its administration and peak at about 60 minutes after the bolus has been administered.
The ICP-lowering effects of a single bolus may last for 6 to 8 hours. Mannitol has many other neuroprotective properties. It is an effective volume expander in the presence of hypovolemic hypotension and therefore may maintain systemic blood pressure required for adequate cerebral perfusion. It also promotes CBF by reducing blood viscosity and microcirculatory resistance. Mannitol reduces RBC deformity and therefore improves oxygen carrying capacity. It is an effective free radical scavenger, reducing the concentration of oxygen free radicals that may promote cell membrane lipid peroxidation.