Magnesium sulfate tocolysis and pulmonary edema: the drug or the vehicle?

This study was undertaken to determine the: (1) risk factors for developing pulmonary edema associated with magnesium sulfate (MgSO4) tocolysis; (2) mean latency period to diagnosis; (3) role of maternal transport; and (4) safety of continued therapy.

A total of 150 antenatal patients treated for preterm labor with MgSO4 were identified for this retrospective, case-control study. Cases were compared 1:2 with controls in regard to maternal demographics, MgSO4 concentration and infusion rates, maternal transport status, and maternal net fluid balance.

Risk factors for developing pulmonary edema include: greater MgSO4 and intravenous fluid infusion rates, less concentrated MgSO4, infection, multiple gestations, concomitant tocolytics, large positive net fluid balances, and maternal transport. The mean latency period to diagnosis was 1.96 days. Six percent of patients had recurrence if MgSO4 tocolysis was continued.

MgSO4 and intravenous fluid rates are both associated with the development of pulmonary edema. Once appropriately treated, MgSO4 tocolysis can be continued with little risk of recurrence.