• Feng Fu, Yu-Wen Tang, Hong Chen, Cui-Cui Jiao, Na Ma, and Xin-Zhong Chen.
• Department of Anesthesia, Women's Hospital, Zhejiang University School of Medicine, Xueshi Rd 1#, Hangzhou, China.
• BMC Anesthesiol. 2020 Aug 12; 20 (1): 198.

Backgroundα-receptor agonists have been reported to be safe and effective for treating or preventing spinal-induced hypotension during cesarean delivery. As a pure α1 adrenergic agonist, methoxamine has potential advantages of reducing myocardial oxygen consumption and protecting the heart in obstetric patients compared to phenylephrine. The aim of this study was to determine the optimal prophylactic methoxamine infusion dose that would be effective for preventing spinal-induced hypotension in 50% (ED50) and 95% (ED95) of parturients.MethodsEighty parturients with a singleton pregnancy scheduled for elective cesarean delivery were randomly allocated to receive prophylactic methoxamine infusion at one of four different fixed-rates: 1 μg/kg/min (group M1), 2 μg/kg/min (group M2), 3 μg/kg/min (group M3), or 4 μg/kg/min (group M4). An adequate response was defined as absence of hypotension (maternal SBP < 80% of baseline or SBP < 90 mmHg). The values for ED50 and ED95 of prophylactic methoxamine infusion were determined by probit regression model. The outcomes of maternal hemodynamics and fetal status were compared among the groups.ResultsThe calculated ED50 and ED95 (95% confidence interval) of prophylactic methoxamine infusion dose were 2.178 (95% CI 1.564 to 2.680) μg/kg/min and 4.821 (95% CI 3.951 to 7.017) μg/kg/min, respectively. The incidence of hypotension decreased with increasing methoxamine infusion dose (15/20, 11/20, 7/20 and 2/20 in group M1, M2, M3 and M4 respectively, P <  0.001). 1-min Apgar scores and umbilical arterial PaO2 were lower but umbilical arterial PaCO2 was higher in Group M1. No difference was found in the other incidence of adverse effects and neonatal outcomes among groups.ConclusionsUnder the conditions of this study, when prophylactic methoxamine infusion was given at a fixed-rate based on body weight for preventing spinal-induced hypotension in obstetric patients, the values for ED50 and ED95 were 2.178 μg/kg/min and 4.821 μg/kg/min respectively.Clinical Trial RegistrationChinese Clinical Trial Registry (ChiCTR), registry number of clinical trial: ChiCTR-1,800,018,988 , date of registration: October 20, 2018.

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