• Ngan KeeWarwick DWDFrom the Department of Anaesthesia and Intensive Care, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, Hong Kong, China (W.D.N.K., F.F.N., P.E.T., K.S.K.); and Department of Health Technology and Informatics, The , Shara W Y Lee, Floria F Ng, Perpetua E Tan, and Kim S Khaw.
• From the Department of Anaesthesia and Intensive Care, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, Hong Kong, China (W.D.N.K., F.F.N., P.E.T., K.S.K.); and Department of Health Technology and Informatics, The Hong Kong Polytechnic University, Kowloon, Hong Kong, China (S.W.Y.L.).
• Anesthesiology. 2015 Apr 1; 122 (4): 736-45.

BackgroundDuring spinal anesthesia for cesarean delivery, phenylephrine can cause reflexive decreases in maternal heart rate and cardiac output. Norepinephrine has weak β-adrenergic receptor agonist activity in addition to potent α-adrenergic receptor activity and therefore may be suitable for maintaining blood pressure with less negative effects on heart rate and cardiac output compared with phenylephrine.MethodsIn a randomized, double-blinded study, 104 healthy patients having cesarean delivery under spinal anesthesia were randomized to have systolic blood pressure maintained with a computer-controlled infusion of norepinephrine 5 μg/ml or phenylephrine 100 μg/ml. The primary outcome compared was cardiac output. Blood pressure heart rate and neonatal outcome were also compared.ResultsNormalized cardiac output 5 min after induction was greater in the norepinephrine group versus the phenylephrine group (median 102.7% [interquartile range, 94.3 to 116.7%] versus 93.8% [85.0 to 103.1%], P = 0.004, median difference 9.8%, 95% CI of difference between medians 2.8 to 16.1%). From induction until uterine incision, for norepinephrine versus phenylephrine, systolic blood pressure and stroke volume were similar, heart rate and cardiac output were greater, systemic vascular resistance was lower, and the incidence of bradycardia was smaller. Neonatal outcome was similar between groups.ConclusionsWhen given by computer-controlled infusion during spinal anesthesia for cesarean delivery, norepinephrine was effective for maintaining blood pressure and was associated with greater heart rate and cardiac output compared with phenylephrine. Further work would be of interest to confirm the safety and efficacy of norepinephrine as a vasopressor in obstetric patients.

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