Magnesium sulphate is given intravenously to prevent initial or subsequent eclamptic fits in peripartum women. Its efficacy in fit prophylaxis is unquestioned but when it should be commenced and stopped are challenging questions. Two American surveys help in the decision making process in high-risk hypertensive patients.
Alexander et al from Texas (Obstet Gynecol 2006;826-32) reviewed their unit's records when changing from an intramuscular to an intravenous regime and at the same time from treating all hypertensive women to treating only those qualifying for treatment according to strict criteria which would label them as severe preeclamptics. The criteria used were
* BP of 140/90 in a previously normotensive woman
* proteinuria of 2+ or greater on a catheter specimen
* serum creatinine more than 1.2mg/dl or platelets less than 100 000/ml
* aspartate transaminase of double the upper limit of normal
* persistent headache or visual disturbances
* persistent epigastric or right upper-quadrant pain.
As expected, the selective rather than broad spectrum use of magnesium resulted in more eclamptic fits but the numbers needed to treat and the side effects of magnesium therapy make an optimal policy difficult to set. If the net is too fine, it cannot be dragged through the water, and the authors speak of an “irreducible minimum” of unpreventable cases.
A second study from Ohio looked at the duration of magnesium treatment postpartum in mild preeclamptics. Ehrenberg & Mercer (pp833-8) randomly allocated women receiving prophylactic magnesium sulphate but who did not have severe disease, to have 12 or 24 hours of postpartum treatment. Women whose condition deteriorated after being selected to one or other arm of the trial were immediately excluded. Incidentally they found that chronic hypertensive and insulin-dependent diabetics were the most at-risk groups for such deterioration.
Of those not showing progressive disease, it seemed that 12 hours of treatment was sufficient and that carrying on the magnesium for a total of 24 hours had no advantage. Of course, lesser duration of treatment means fewer intensive nursing hours, less chance of side-effects and less maternal mobility, so this article provides useful practical information.
