Pressure-volume conditions in patients with subarachnoid and/or intraventricular hemorrhage

Pressure-volume conditions were studied in 17 patients with subarachnoid and/or intraventricular hemorrhage, who underwent continuous intracranial pressure (ICP) monitoring. The pressure-volume index (PVI) technique was used. The interrelationship between the ICP pulse amplitude and compliance was also examined. All patients were admitted in Hunt and Hess Grades II to V, and 11 had a proven aneurysm. The ICP was above 15 mm Hg in all patients during some part of the monitoring period. The pressure-volume conditions were abnormal in all patients. Median PVI was 12.7 ml (5.8 to 40.0 ml). The PVI did not correlate with ICP: the PVI based on bolus injection was significantly greater than PVI based on fluid withdrawal. The ICP pulse amplitude varied from 1.5 to 15 mm Hg and rose concomitantly with increasing ICP. Considering the pulsatile shift in intracranial blood volume as an endogenous bolus that increases ICP from the diastolic (Pdiast) to the systolic (Psyst) level, an equation was derived from the PVI model that describes the relationship between the Psyst:Pdiast ratio and the PVI.