Objective: This study was undertaken to compare the persistence of changes in estimated cerebral perfusion pressure and the resistance area product, an index of cerebrovascular resistance, in women with preeclampsia and women with eclampsia.
Study design: The maternal middle cerebral artery was evaluated by transcranial Doppler ultrasonography in 6 patients with severe preeclampsia and 3 women with eclampsia, and cerebral blood flow velocities were determined. Estimated cerebral perfusion pressure was calculated according to the following equation: Estimated cerebral perfusion pressure = Mean cerebral blood flow velocity/(Mean cerebral blood flow velocity - Diastolic cerebral blood flow velocity) x (Mean blood pressure - Diastolic blood pressure). Because the diameters of the vessels could not be measured directly, an index of resistance was calculated according to the following equation: Resistance area product = Mean blood pressure/Mean cerebral blood flow velocity. We calculated an index of cerebral blood flow according to the following equation: Index = Estimated cerebral perfusion pressure/Resistance area product. Patients were reassessed at 24 and 48 hours after delivery.
Results: At the initial assessment the estimated cerebral perfusion pressure was higher in women with eclampsia than in those with severe preeclampsia. In addition, cerebrovascular resistance was significantly decreased in the eclampsia group, and it remained decreased as long as 4 days in 1 patient with eclampsia.
Conclusions: Preeclampsia is associated with increases in cerebral perfusion pressure counterbalanced by increases in cerebrovascular resistance, with no change in cerebral blood flow. In eclampsia a significant increase in cerebral perfusion pressure occurs, but a significant fall in cerebrovascular resistance also occurs and a loss of autoregulation results in cerebral overperfusion similar to that of hypertensive encephalopathy. This may persist for as long as 4 days.