What causes pulmonary edema on magnesium sulfate for early labor?

Cardiac depression.: Magnesium sulfate acts as a cardiac depressant and can send a pregnant woman into pulmonary edema, especially if additional factors are present: preeclampsia, twins, obesity, smoking, overdose with magnesium sulfate. Diuresis with Lasix (furosemide) and prompt discontinuation of the magnesium infusion drip will reverse this life-threatening complication rather rapidly. A cardiac echo is warranted.

Other factors: Magnesium sulfate by itself do not cause pulmonary edema. It is use for preeclampsia - condition during pregnancy which can cause kidney or heart disease ( both of them can present with pulmonary edema ). It is also use as a tocolytic agent ( slow down contractions in premature labor ). Other tocolytic agent ( terbutaline ) is more likely to cause pulmonary edema and then it can be used instead.