Metaraminol Infusion for Maintenance of Arterial Blood Pressure During Spinal Anesthesia for Cesarean Delivery: The Effect of a Crystalloid Bolus

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Abstract
We randomly allocated women having elective cesarean delivery to receive either no bolus (Control Group, n = 31) or 20 mL/kg lactated Ringer’s solution (Bolus Group, n = 35) IV before spinal anesthesia. An infusion of metaraminol started at 0.25 mg/min was titrated to maintain systolic arterial blood pressure in the target range 90%–100% of baseline. The total dose of metaraminol required up to the time of uterine incision was similar between the Control Group and the Bolus Group (3.62 ± 1.20 vs 3.27 ± 1.39 mg, P = 0.3). However, the Control Group required more metaraminol in the first 5 min (1.29 ± 0.60 vs 0.96 ± 0.58 mg, P = 0.025) and a faster maximum infusion rate (0.45 ± 0.20 vs 0.32 ± 0.13 mg/min, P = 0.002) compared with the Bolus Group. There was no difference between groups in regards to changes in systolic arterial blood pressure or heart rate over time, or maternal or neonatal outcome. We conclude that when metaraminol is used to maintain arterial pressure during spinal anesthesia for cesarean delivery, crystalloid bolus is not essential provided that sufficient vasopressor is given in the immediate postspinal period.