Does magnesium sulfate affect the oxytocin bolus requirement in pre-eclamptic patients undergoing cesarean section?

Objective The aim of this study was to determine whether the magnesium sulfate (MgSO4) used for preeclamptic patients affects the oxytocin bolus dose requirement to maintain adequate uterine tone during cesarean section under spinal anesthesia. Materials and methods A total of 80 patients with mild pre-eclampsia were randomized to receive either intravenous MgSO4 (group M, n = 40) or matched normal saline (group S, n = 40). After delivery of the baby, oxytocin was injected as an intravenous bolus of 3 IU. The uterine tone was assessed by the obstetrician to be either satisfactory or unsatisfactory at 2, 4, 6, 8, and 10 min. If the tone was assessed as unsatisfactory at any time less than 3 IU of oxytocin were injected as a ‘rescue’ bolus dose. A maximum of two ‘rescue’ doses of oxytocin were allowed at two separate recordings of inadequate uterine tone. If the uterine tone was still unsatisfactory after two rescue doses of oxytocin, then other uterotonic drugs were given. The primary endpoint was the number of patients who received rescue doses of oxytocin or other uterotonic medications. Secondary endpoints, including the change in the hematocrit value before surgery and within 30 min after cesarean section, the estimated amount of intraoperative blood loss, and any side effects associated with oxytocin, were recorded. Results The number of patients who required one rescue dose of oxytocin during the study was significantly higher in group M in comparison with group S (P = 0.029). The total number of patients who received both additional oxytocin boluses and other uterotonic agents to achieve a satisfactory uterine tone was also statistically significant between both groups (P = 0.034). Conclusion The use of MgSO4 in mild pre-eclamptic patients leads to increased oxytocin requirements in order to maintain a satisfactory uterine tone during cesarean section under spinal anesthesia.