Changes in cerebral perfusion pressure in puerperal women with preeclampsia.

OBJECTIVE: To determine the variation in the estimated maternal cerebral perfusion and cerebrovascular resistance (the resistance area product) in the puerperium. METHODS: The maternal middle cerebral artery was evaluated by transcranial Doppler ultrasound in ten women 2 days before labor, in 21 women in early labor and at 24 and 48 hours postpartum, and in 6 women at 1 week postpartum. Cerebral blood flow velocities were determined. Women were diagnosed initially with mild preeclampsia. Estimated cerebral perfusion pressure was Vmean/[Vmean - Vdiastolic] [BPmean - BPdiastolic]. Because the diameter of the vessels could not be measured directly, an index of resistance was calculated: the resistance area product = BPmean/velocitymean. We calculated an index of cerebral blood flow to be estimated cerebral perfusion pressure divided by resistance area product. Our study had a power of 80% to detect a 16-cm/second increase in middle cerebral blood flow velocity. RESULTS: Estimated maternal cerebral perfusion was maintained for up to 1 week postpartum. Cerebrovascular resistance did not change in the puerperium. Cerebral blood flow index (+/-standard deviation) was significantly increased at 1 week postpartum compared with early labor levels (28.3 +/-6.9 versus 46.7+/-15.6, respectively) (P < .05). CONCLUSION: Cerebral blood flow 1 week postpartum increased significantly over early labor values. These persistent changes in the cerebral vasculature might put patients at risk for seizures up to 1 week postpartum.

Maternal transcranial Doppler in pre-eclampsia and eclampsia.

Pre-eclampsia affects 3-7% of women and is associated with significant maternal and perinatal morbidity and mortality. Transcranial Doppler (TCD) has been used in pre-eclampsia/eclampsia to evaluate non-invasively the cerebrovascular hemodynamics in the maternal middle cerebral artery. TCD has demonstrated in pre-eclamptic women maternal cerebral vasospasm, which does not correlate with mean arterial pressure assessed simultaneously. Estimated cerebral perfusion pressure, assessed using a modified formula, has been shown to be increased in women with severe and non-severe pre-eclampsia. However, in severe pre-eclampsia, elevated cerebral perfusion pressure is counterbalanced by increases in cerebrovascular resistance and cerebral blood flow is unaffected. In eclampsia a significant fall in cerebral vascular resistance occurs which, in the presence of increases in cerebral perfusion pressure, leads to hyperperfusion. Cerebral vascular changes to date have not been sensitive enough to predict the development of pre-eclampsia or eclampsia. Longitudinal studies with the aim of predicting the onset of pre-eclampsia and to assess the effects of various drugs on the maternal cerebral circulation need to be designed.

Effect of labor on maternal cerebral blood flow velocity.

OBJECTIVE: Our purpose was to determine the effect of contractions and second-stage pushing on cerebral blood flow velocity as an indirect assessment of cerebral hemodynamic changes during labor and delivery. STUDY DESIGN: A prospective cohort of 15 normotensive patients in early labor had maternal middle cerebral blood flow velocity assessed continuously with transcranial Doppler ultrasonography. Assessment was performed during the peak of a contraction, during the trough of a contraction, and with pushing in the second stage. We assessed systolic, diastolic, mean cerebral blood flow velocity (in centimeters per second), and pulsatility index over four contractions. We used analysis of variance to compare velocities at these three stages. RESULTS: Mean maternal cerebral blood flow velocity fell significantly (61.2 +/- 6.4, 50 +/- 10.2, 52.2 +/- 6.5 cm/sec) (p < 0.008). Pulse rate rose significantly by 16 beats/min (p < 0.0001), but no significant change in blood pressure occurred in patients during second-stage labor when pushing. CONCLUSIONS: Middle cerebral vessels vasodilated during the peak of contractions and second-stage pushing as assessed by transcranial Doppler ultrasonography. Pushing in the second stage with the Valsalva maneuver does not expose the patient to a greater risk for middle cerebral vasospasm than contractions developing in the first stage.