Pre-eclampsia, magnesium sulfate, and blood pressure evaluation during labor: a preliminary consideration.

The influences of uterine contractions and magnesium sulfate (MgSO4) infusion on blood pressure evaluation of the pre-eclamptic patient in labor have not been thoroughly investigated. Blood pressures were measured between and during contractions in 13 patients with pre-eclampsia, before and after MgSO4, and in 17 normotensive patients. Pre-eclampsia was associated with a mean 11 mm Hg increase in pulse pressure (P less than 0.001), which fell by 8 mm Hg following MgSO4 infusion (P less than 0.001). With pre-eclampsia, pressure increases up to 45/28 mm Hg were observed during contractions. Theoretically, reduced pulse pressure, resulting in decreased shearing force applied to vessel walls, could be a previously unrecognized therapeutic effect of MgSO4. Potentially dangerous pressure elevations could be missed by relying exclusively on diastolic values measured between contractions.