Pressure-volume index as a function of cerebral perfusion pressure. Part 1: The effects of cerebral perfusion pressure changes and anesthesia.

The pressure-volume index (PVI) was measured as a function of cerebral perfusion pressure (CPP) in 12 adult cats. Anesthesia was induced with methohexital in six animals and with pentobarbital in six animals; all were maintained on an N2O:O2 (70%:30%) mixture. The CPP was either increased in 10-torr increments using norepinephrine or decreased by a combination of adenosine triphosphate and hemorrhage in subgroups. Three estimations of PVI were made at each level of CPP. The PaCO2, body temperature, and hematocrit were controlled at normal levels throughout. In both groups there was a linear relationship between PVI and CPP with increasing CPP being reflected by a rise in PVI. This relationship was more marked in the methohexital group: PVI = 0.37 ml + 0.0005 mm Hg CPP in the pentobarbital group, and PVI = 0.14 ml + 0.0019 mm Hg CPP in the methohexital group. These results indicate that the PVI is not independent of CPP but is a function of CPP and is profoundly influenced by anesthesia.