Bolus norepinephrine and phenylephrine for maternal hypotension during elective cesarean section with spinal anesthesia: a randomized, double-blinded study

Background: In recent years, norepinephrine has attracted increasing attention for the management of maternal hypotension during elective cesarean section with spinal anesthesia. Intermittent bolus is a widely used administration paradigm for vasopressors in obstetric anesthesia in China. Thus, in this randomized, double-blinded study, we compared the efficacy and safety of equivalent bolus norepinephrine and phenylephrine for rescuing maternal post-spinal hypotension.Methods: In a tertiary women’s hospital in Nanjing, China, 102 women were allocated with computer derived randomized number to receive prophylactic 8 μg norepinephrine (group N;n = 52) or 100 μg phenylephrine (group P;n = 50) immediately post-spinal anesthesia, followed by an extra bolus of the same dosage until delivery whenever maternal systolic blood pressure became lower than 80% of the baseline. Our primary outcome was standardized maternal cardiac output (CO) reading from spinal anesthesia until delivery analyzed by a two-step method. Other hemodynamic parameters related to vasopressor efficacy and safety were considered as secondary outcomes. Maternal side effects and neonatal outcomes were collected as well.Results: Compared to group P, women in group N had a higher CO (standardized CO 5.8 ± 0.9vs. 5.3 ± 1.0 L/min,t = 2.37,P = 0.02) and stroke volume (SV, standardized SV 73.6 ± 17.2vs. 60.0 ± 13.3 mL,t = 4.52,P < 0.001), and a lower total peripheral resistance (875 ± 174vs. 996 ± 182 dyne·s/cm5,t = 3.44,P < 0.001). Furthermore, the incidence of bradycardia was lower in group N than in group P (2%vs. 14%,P= 0.023), along with an overall higher standardized heart rate (78.8 ± 11.6vs. 75.0 ± 7.3 beats/min,P = 0.049). Other hemodynamics, as well as maternal side effects and neonatal outcomes, were similar in two groups (P > 0.05).Conclusions: Compared to equivalent phenylephrine, intermittent bolus norepinephrine provides a greater CO for management of maternal hypotension during elective cesarean section with spinal anesthesia; however, no obvious maternal or neonatal clinical advantages were observed for norepinephrine.