[PVI in analyzing pressure volume relationship--effect of a bolus mannitol administration]

It has been considered that mannitol reduces a raised intracranial pressure effectively by improving pressure volume relationship. The objective of this study is to determine how the pressure volume status is changed by a bolus mannitol administration with using several biomechanical parameters (intracranial pressure, pressure volume index, and intracranial elastance). Our data indicated that mannitol changed the PVI more sensitively than ICP and elastance. "Estimated Intracranial Volume Change (EICVC)" has been newly defined during mannitol infusion on the basis of PVI and ICP change. EICVC for first 30 minutes-period at which the intracranial pressure most vigorously decreased was only about 5 ml in volume. The temporal course of EICVC and ICP were not different, thus, it could account for the change of ICP properly. However, the temporal course of PVI indicating the intracranial venous blood pooling, can not be explained only by EICVC since the PVI has been changed more rapidly than any other parameters. Therefore, we speculated that the ratio of intracranial components could be more largely altered by mannitol than the net of intracranial volume change. The fundamental mechanism of ICP reduction by mannitol is possibly the brain water movement into venous circulation.