Ephedrine vs. phenylephrine by intravenous bolus and continuous infusion to prevent hypotension secondary to spinal anesthesia during cesarean section: a randomized comparative trial

Objective: Subarachnoid spinal anesthesia for cesarean section is associated with a high incidence of hypotension, which can require the use of vasoconstrictors. The aim of this trial was to compare ephedrine to phenylephrine for the prevention of secondary hypotension and to assess the adverse effects on both mother and newborn. Material and methods: Eighty patients undergoing elective or emergency cesarean section, in the absence of uterine activity or fetal risk, were randomized to receive prophylaxis with ephedrine or phenylephrine immediately after the spinal block. Patients in the ephedrine group received an intravenous bolus of 0.1 mg/kg plus continuous infusion at a rate of 0.5 mg/kg/h; patients in the phenylephrine group received an intravenous bolus of 1.5 mu g/kg plus a continuous infusion at 1.5 mu g/kg/min. Infusion was maintained until umbilical cord clamping. We recorded maternal blood pressure, heart rate, nausea and vomiting, dizziness, bradycardia, hypotension, hypertension, fetal Apgar index, and umbilical cord blood parameters (pH, PCO2, and HCO3). Results: The overall incidence of hypotension was 11.2%, with no significant between-group differences (ephedrine group, 11.4%; phenylephrine group, 11.1%). The incidences of hypertension and bradycardia were higher in the phenylephrine group (27.8% and 2.3%, respectively) than in the ephedrine group (25% and 0%, respectively). Umbilical cord blood parameters and Apgar scores were similar. After suspension of continuous infusion, an episode of hypotension was detected in 22.5% of the patients (72.2% of these patients were in the phenylephrine group and 27.8% were in the ephedrine group). Conclusions: At the doses of ephedrine and phenylephrine administered in this trial, the ability of these drugs to prevent hypotension during cesarean section proved to be similar. Higher incidences of adverse events (hypertension and bradycardia) were observed in the phenylephrine group. No differences were observed in neonatal effects.