[The mechanism of intracranial pressure-reducing effect of mannitol].

The effect of mannitol to decrease the raised ICP is well documented and mannitol is now widely used in clinical practice. However, its mechanism of lowering ICP still remains controversial, especially under the condition of vasogenic edema. The objective of this study is to reexamine and delineate the mechanism of ICP reducing effect of mannitol, using quantitative vasogenic edema model, specific gravimetric technique to measure the brain water content, and the method to estimate the CSF dynamics without disturbing the physiological condition of intracranial compartments in cats. Quantitative increase of water content of the white matter was produced by the infusion of 0.5 ml of normal saline though stereotaxically inserted 25-G needle into the left frontal white matter. In control group, cats were sacrificed and water content of the gray and white matter of each coronary sliced brain was measured by specific gravimetric technique. In the mannitol group, 20% of mannitol (2 g/kg) was administrated via femoral vein within 3 minutes. The maximum reduction of ICP was achieved at the average of 30 minutes. At this time, the cats were sacrificed and the water content of brain was measured in the same way as in the control group. PVI, Ro, If (Marmarou) were calculated before and after mannitol administration. In parameter group, BP, ICP, CVP, serum osmotic pressure and osmolarity were measured without terminating the experiment. The changes of water content of the gray and white matter before and after mannitol administration in the area of infusion edema were 80.7% to 80.8% and 76.8% to 77.1% respectively.(ABSTRACT TRUNCATED AT 250 WORDS)