Magnesium sulfate decreases cerebral perfusion pressure in preeclampsia.

OBJECTIVE

To determine the cerebral hemodynamic effect of magnesium sulfate (MgSO4) in preeclampsia.

DESIGN

Prospective observational study.

SETTING

Tertiary Care Medical Center.

POPULATION: Preeclamptic patients (systolic < 160, diastolic < 110 mmHg).

METHODS

Transcranial Doppler (TCD) of the middle cerebral arteries (MCA) of 15 preeclamptics, before and after IV MgSO4. No vasoactive drugs other than MgSO4 were given. 11 patients with mild range BP (140/90-160/110 mmHg) had measurements at baseline, 30 and 120 minutes after MgSO4, and 7 patients with elevated CPP had baseline and 30 minute measurements. Hemodynamic parameters were compared with normative curves.

MAIN OUTCOME MEASURES: Mean arterial pressure (MAP), heart rate (HR), cerebral perfusion pressure (CPP), resistance index (RI), resistance area product (RAP), and cerebral flow index (CFI).

RESULTS

Eight women had normal baseline CPP, and 11 had normal CFI. 11 had mild preeclampsia range blood pressure and MgSO4 had no significant effect on CPP, CFI, HR, MCA velocities, or RAP but did decrease the MAP in the first 30 minutes (107 +/- 8 to 100 +/- 9 mmHg; p = 0.035), mainly due to a drop in diastolic pressure (87 +/- 10 to 82 +/- 9 mmHg; p = 0.004). 7 patients with elevated baseline CPP had a significant reduction in CPP, but no change in CFI, after MgSO4.

CONCLUSIONS

MgSO4 does not significantly effect CPP or CFI in preeclamptics with baseline blood pressure in the mild range, but does significantly reduce CPP in those with high baseline CPP. This may be important in the prevention of hypertensive encephalopathy.