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Li-Juan Hu,1 Zhong Mei,1,2 Yan-Ping Shen,1 Hao-Tian Sun,1 Zhi-Min Sheng,1 Xin-Zhong Chen,1 Xiao-Wei Qian1 1Department of Anesthesiology, Women’s Hospital, Zhejiang University School of Medicine, Hangzhou, People’s Republic of China; 2Department of Anesthesiology, Affiliated Xiaoshan Hospital, Hangzhou Normal University, Hangzhou, People’s Republic of ChinaCorrespondence: Xiao-Wei Qian, Department of Anesthesiology, Women’s Hospital, Zhejiang University School of Medicine, Xueshi Road 1, Hangzhou, 310006, People’s Republic of China, Tel +86-571-87061501, Fax +86 571 87061878, Email qianxw@zju.edu.cnBackground: It is well-known that severe preeclamptic parturients have less vasopressor requirements than normotensive parturients; however, the exact dose difference is poorly documented. This study aimed to determine and compare the ED50 and ED90 of a single bolus phenylephrine for the treatment of spinal anesthesia-induced hypotension in parturients with severe preeclampsia and parturients with normotension.Methods: Seventy-five parturients with severe preeclampsia scheduled for cesarean delivery under combined spinal-epidural anesthesia were enrolled and randomly allocated to receive a single bolus of phenylephrine at five different doses (40, 50, 60, 70, and 80 μg), whereas 75 parturients with normotension were randomized to receive a single bolus of phenylephrine at five different doses (70, 80, 90, 100, and 110 μg) for the treatment of the first episode of hypotension. Phenylephrine dose values were log-transformed, the proportions of the successful interventions at each dose were converted to probits, and regression analysis was performed.Results: The ED50 and ED90 (95% CI) of bolus phenylephrine were 72.1 (61.7 to 79.9) μg and 107 (95.9– 128.6) μg in parturients with normotension. The ED50 and ED90 values in parturients with severe preeclampsia were 47.6 (41.3– 52.7) μg and 70.7 (62.9– 86.7) μg. The relative median potency was 1.51 (1.16– 2.61).Conclusion: Under this study conditions, severe preeclamptic parturients required a 34% reduction of ED50 of phenylephrine dose compared with normotensive parturients.Keywords: cesarean delivery, spinal anesthesia, hypotension, phenylephrine, preeclampsia