The effects of prophylactic bolus phenylephrine on hypotension during low-dose spinal anesthesia for cesarean section

BackgroundContinuously infused phenylephrine is frequently used to reduce the incidence of hypotension in women undergoing cesarean section under spinal anesthesia, but less is known about the prophylactic bolus method. We evaluated three prophylactic bolus doses of phenylephrine during low-dose spinal anesthesia for cesarean section.MethodsOne-hundred-and-eighty-four patients were randomized to receive 0.9% saline 2 mL (Control Group) or phenylephrine 1.0 μg/kg (PHE1 Group), 1.5 μg/kg (PHE1.5 Group), or 2.0 μg/kg (PHE2 Group) immediately after induction of combined spinal-epidural anesthesia. Maternal blood pressure and heart rate were recorded at 1-min intervals until delivery. Hypotension, defined as systolic blood pressure <80% of baseline, was treated with rescue doses of phenylephrine 100 μg at 1-min intervals until hypotension resolved. The incidence of nausea, vomiting, bradycardia, and hypertension, as well as Apgar scores and umbilical blood gases, were recorded.ResultsThe incidence of hypotension was 71.7% (33/46) in the Control Group, 68.9% (31/45) in the PHE1 Group, 37.0% (17/46) in the PHE1.5 Group and 45.7% (21/46) in the PHE2 Group (P=0.001). The total rescue dose of phenylephrine was greater in the Control Group than those in the PHE1.5 Group (P <0.05) and PHE2 Group (P <0.05). The incidence of hypertension increased as the dose of prophylactic phenylephrine increased (P <0.001) and was highest in the PHE2 group (37%). Other variables did not differ among the four groups.ConclusionsUnder the conditions of this study, prophylactic bolus injection of phenylephrine 1.5 μg/kg was a suitable alternative method for reducing the incidence of hypotension during low-dose spinal anesthesia for cesarean section.