Comparative dose--response study on norepinephrine infusion for preventing hypotension during spinal anaesthesia for caesarean delivery in singleton versus twin pregnancies: A randomized, double-blind, controlled, dose-finding trial

Intravenous initial bolus during prophylactic norepinephrine infusion to prevent spinal hypotension for cesarean delivery: A randomized controlled, dose-finding trial

BACKGROUND

Previous studies have shown that a 0.05 μg/kg/min of norepinephrine infusion in combination with an initial bolus reduces the incidence of spinal hypotension during cesarean delivery. The initial norepinephrine bolus influences the incidence of spinal hypotension during continuous norepinephrine infusion; however, the ideal initial bolus dose for 0.05 μg/kg/min of continuous infusion remains unknown.

METHODS

This randomized, controlled, dose-finding study randomly allocated 120 parturients scheduled for elective cesarean delivery to receive initial bolus doses of 0, 0.05, 0.10, and 0.15 μg/kg of norepinephrine, followed by continuous infusion at a rate of 0.05 μg/kg/min. The primary outcome was the dose-response relationship of the initial norepinephrine bolus in preventing the incidence of spinal hypotension. Spinal hypotension was defined as systolic blood pressure (SBP) decreased to <80% of the baseline value or to an absolute value of <90 mmHg from intrathecal injection to delivery, and severe spinal hypotension was defined as SBP decreased to <60% of the baseline value. The secondary outcomes included the incidence of nausea and/or vomiting, hypertension, and bradycardia, as well as the Apgar scores and results of the umbilical arterial blood gas analysis. The effective dose (ED) 90 and ED95 were estimated using probit regression.

RESULTS

The per-protocol analysis included 117 patients. The incidence of spinal hypotension varied significantly among the groups: Group 0 (51.7%), Group 0.05 (44.8%), Group 0.10 (23.3%), and Group 0.15 (6.9%). The ED90 and ED95 values were 0.150 μg/kg (95% confidence interval [CI], 0.114-0.241 μg/kg) and 0.187 μg/kg (95% CI, 0.141-0.313 μg/kg), respectively. However, the ED95 value fell outside the dose range examined in this study. The incidence of severe spinal hypotension differed significantly (P = 0.02) among Groups 0 (17.2%), 0.05 (10.3%), 0.10 (3.3%), and 0.15 (0.0%); however, the incidence of hypertension and bradycardia did not. The incidence of nausea and/or vomiting decreased with an increase in the initial bolus dose (P = 0.03). The fetal outcomes were comparable among the groups.

CONCLUSIONS

An initial bolus of 0.150 μg/kg of norepinephrine may be the optimal dose for preventing spinal hypotension during cesarean delivery with a continuous infusion rate of 0.05 μg/kg/min, and does not significantly increase the incidence of hypertension but substantially reduces the risk of nausea and/or vomiting.

Prophylactic intravenous norepinephrine for the prevention of hypotension during spinal anesthesia for elective cesarean section: a systematic review and dose-response meta-analysis of randomized controlled trials

Introduction: In this study, we aimed to evaluate the potential dose-response relationship between prophylactic norepinephrine (NE) infusion rates and the risks of hypotension during cesarean section following spinal anesthesia. Methods: Randomized controlled trials with two or more NE doses for post-spinal hypotension prophylaxis during cesarean section were systematically searched in the MEDLINE, Embase, Web of Science, Cochrane Central Register of Controlled Trials, and US Clinical Trials Registry databases until 31 July 2022. The primary outcome was the relative risk of maternal hypotension with different NE regimens (infusion rates or bolus doses). Secondary outcomes included the relative risks of maternal and fetal adverse events with different NE regimens. Results: Ten studies with 1,144 parturients were included for final analysis using restricted cubic splines and random-effects dose-response meta-analysis models. A significant dose-response relationship existed between NE infusion rates and the relative risks of maternal hypotension. Every 0.01 μg/kg/min increment in the NE infusion rate was associated with a 14% decrease in the incidence of post-spinal hypotension. ED50 and ED95 of NE infusion rates for post-spinal hypotension prophylaxis were estimated to be 0.046 (95% CI from 0.032 to 0.085) and 0.2 (95% CI from 0.14 to 0.37) μg/kg/min, respectively. However, a higher NE infusion rate was associated with a higher incidence of maternal hypertension. Conclusion: An increased NE infusion rate was associated with a decreased incidence of post-spinal hypotension but an increased incidence of hypertension. Therefore, 0.07 μg/kg/min was recommended as the initial NE infusion rate for clinical practice, as it was associated with the lowest risk of physician intervention for unstable hemodynamics after spinal anesthesia for cesarean delivery. Systematic Review Registration: (https://www.crd.york.ac.uk/PROSPERO/display_record.php?RecordID=349934), identifier (CRD42022349934).