Comparison of prophylactic bolus norepinephrine and phenylephrine on hypotension during spinal anesthesia for cesarean section

Background and objective: Phenylephrine is the first-line choice for prevention and treatment of hypotension during spinal anesthesia for cesarean section. However, the serious bradycardia caused by phenylephrine is a concern. This study compared the effects of prophylactic bolus norepinephrine and phenylephrine on hypotension during spinal anesthesia for cesarean section. Methods: A total of 132 healthy parturients having cesarean section under spinal anesthesia were enrolled in this prospective, randomized, double-blinded, parallel-group trial. Patients were randomized to receive prophylactic bolus norepinephrine (10 mu g) or phenylephrine (50 mu g) immediately after spinal anesthesia. The primary outcome compared was incidence of bradycardia (defined as heart rate <60 beats/min). The secondary outcomes were blood pressure, heart rate, cardiac output, nausea and vomiting, and neonatal outcome. Results: The incidence of bradycardia was significantly lower in the norepinephrine group (2%) than that in the phenylephrine group (13%, P < 0.05). Five patients had heart rate lower than 55 beats/min and needed atropine 0.5 mg administration in the phenylephrine group. Cardiac output at 5 min was significantly greater in the norepinephrine group than that in the phenylephrine group (P < 0.05). From induction until delivery, there were no significant differences in systolic blood pressure. Neonatal outcome was similar between groups. Conclusions: Norepinephrine is as effective as phenylephrine in preventing spinal hypotension but has less adverse effects on heart rate and greater cardiac output than phenylephrine during caesarean section.