Norepinephrine Infusion for Preventing Postspinal Anesthesia Hypotension during Cesarean Delivery: A Randomized Dose-finding Trial.

Background: Norepinephrine has been recently introduced for prophylaxis against postspinal hypotension during cesarean delivery; however, no data are available regarding its optimum dose. The objective of this study is to compare three infusion rates of norepinephrine for prophylaxis against postspinal hypotension during cesarean delivery.

Methods: The authors conducted a double-blinded, randomized, controlled study including full-term pregnant women scheduled for cesarean delivery. Norepinephrine infusion was commenced after subarachnoid block. Patients were randomized into three groups, which received norepinephrine with starting infusion rates of 0.025 μg · kg(-1) · min(-1), 0.050 μg · kg(-1) · min(-1), and 0.075 μg · kg(-1) · min(-1). Infusion was stopped when intraoperative hypertension occurred. The primary outcome was the frequency of postspinal hypotension (defined as decreased systolic blood pressure less than 80% of the baseline reading). The three groups were compared according to the following: systolic blood pressure, heart rate, frequency of intraoperative hypertension, frequency of bradycardia, and neonatal outcomes.

Results: Two hundred eighty-four mothers were included in the analysis. The frequency of postspinal hypotension was lower for both the 0.050-μg · kg(-1) · min(-1) dose group (23/93 [24.7%], odds ratio: 0.45 [95% CI: 0.24 to 0.82], P = 0.014) and the 0.075-μg · kg(-1) · min(-1) dose group (25/96 [26.0%], odds ratio: 0.48 [95% CI:0.26 to 0.89], P = 0.022) compared with the 0.025-μg · kg(-1) · min(-1) dose group (40/95 [42.1%]). The two higher-dose groups (the 0.050-μg · kg(-1) · min(-1) group and the 0.075-μg · kg(-1) · min(-1) group) had higher systolic blood pressure and lower heart rate compared with the 0.025 μg · kg(-1) · min(-1) group. The three groups were comparable in the frequency of intraoperative hypertension, incidence of bradycardia, and neonatal outcomes.

Conclusions: Both the 0.050-μg · kg(-1) · min(-1) and 0.075-μg · kg(-1) · min(-1) norepinephrine infusion rates effectively reduced postspinal hypotension during cesarean delivery compared with the 0.025-μg · kg(-1) · min(-1) infusion rate.