Magnesium Adds Value Beyond Seizure Prevention


CHICAGO — Central arterial compliance is improved following magnesium infusion in women with preeclampsia, according to a prospective, observational study in 70 patients.

“Magnesium may improve perfusion to end organs by decreasing arterial stiffness, suggesting a benefit beyond seizure prophylaxis,” Dr. Dennie Rogers said at the annual meeting of the Society for Maternal-Fetal Medicine.

In a normal pregnancy, arterial compliance increases by 30% in the first trimester and remains elevated until returning to normal levels 6 weeks post partum. Enhanced arterial compliance is part of the normal adaptation to increased intravascular volume during pregnancy. In preeclampsia, this adaptive mechanism is blunted, explained Dr. Rogers, an ob.gyn. at the University of Illinois at Chicago.

The investigators used applanation tonometry to capture radial pulse waveforms at four time points in 70 women with preeclampsia undergoing magnesium therapy for seizure prophylaxis. From these waveforms they derived the aortic waveform and calculated the augmentation pressure (AP) index and augmentation index corrected at 75 beats per minute (Alx@75). The indices are surrogate measures of arterial compliance. The four time points measured were before magnesium administration, 1 hour after a magnesium bolus, 4 hours after maintenance magnesium infusion, and 24 hours after magnesium infusion completion.

The AP and Alx@75 values were significantly lower at all three times points following magnesium administration, compared with pre-magnesium administration, indicating an improvement in radial stiffness, she said. The effect was most pronounced 4 hours after the infusion began, but persisted for 24 hours following magnesium completion. Notably, brachial blood pressures were not clinically or statistically different at any time line, suggesting that arterial compliance cannot be reliably inferred from traditional brachial pressure.

“Our research suggests that central arterial pressure waveforms may better characterize the pulsatile component of the vascular system,” she said. “This may lead to more effective dosing of medications and improved treatment of hypertensive disorders in pregnancy.”

During a discussion of the study, Dr. Rogers noted that use of radial artery pulse waveforms has been validated in nonpregnant populations but not in pregnancy. Session moderator Dr. Norman Gant of the University of Texas at Dallas, said that another team of investigators observed the same findings using magnesium in pregnant women, but these results were not written down.

Disclosures: None was reported.

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