(Anesthesiology 2017;127:934–941)

While phenylephrine is the established preferred vasopressor for maintaining blood pressure during spinal anesthesia for cesarean delivery, it is often associated with decreased heart rate and cardiac output. Both norepinephrine and phenylephrine are potent α-adrenergic agonists, yet norepinephrine also possesses weak β-adrenergic agonist activity. Recent studies have compared phenylephrine with norepinephrine; however, the doses of norepinephrine have varied. This random-allocation, graded dose-response study aimed to determine the relative potencies of norepinephrine and phenylephrine in treatment of hypotension during spinal anesthesia for cesarean delivery.