Does an Earlier or Late Intravenous Injection of Ondansetron Affect the Dose of Phenylephrine Needed to Prevent Spinal-Anesthesia Induced Hypotension in Cesarean Sections?

Abstract

Background

There was controversy about ondansetron can reduce the incidence of spinal-induced hypotension and decrease the consumption of vasopressor in cesarean delivery with spinal anesthesia. We hypothesized that different timing of ondansetron administration may contribute to the controversy. Therefore, we aimed to determine the effect of different timing of ondansetron administration on the dose requirement of preventing phenylephrine via comparing the ED₅₀ of prophylactic phenylephrine.

Methods

Seventy-five parturients were finally enrolled in this prospective, randomized, double-blinded dose finding study. Ondansetron or placebo was administered 5 min or 15 min before intrathecal injection. Up-down allocation method was used to determine the dose of prophylactic phenylephrine for each parturient in the three groups. The initial infusion rate of first patient was 0.5 µg/kg/min. Then, the rate for next patient was varied with increasing or decreasing of 0.05 μg/kg/min according to the response of the previous patient. An effective dose was defined as no hypotension occurred during the study period. An ineffective dose was defined as hypotension occurred during the study period. Study period in this study is from intrathecal injection to neonatal delivery. ED₅₀ of phenylephrine infusion was calculated by probit regression.

Results

The ED₅₀ of intravenous phenylephrine calculated by probit analysis was 0.33 (95% CI 0.20 to 0.38) µg/kg/min and 0.36 (95% CI 0.32 to 0.38) µg/kg/min in group A and B, and 0.41 (95% CI 0.37 to 0.44) µg/kg/min in group C for patients undergoing cesarean delivery with combined spinal-epidural anesthesia.

Conclusion

An earlier administration of 4 mg prophylactic ondansetron contributed no benefits for lowing the dose of prophylactic phenylephrine compared to a late administration, but can decrease the dose of preventing phenylephrine in patients undergoing cesarean delivery with combined spinal-epidural anesthesia. This finding may be useful for clinical practice and further studies.

Keywords:

• ondansetron
• phenylephrine
• cesarean delivery
• spinal anesthesia
• hypotension

Acknowledgments

The authors would thank all staff in the Department of Anesthesia and Operating Room of Jiaxing University Affiliated Women and Children Hospital, Jiaxing, China, for their help in this study. This study was supported by the Jiaxing Science and Technology Bureau Fund (2020AD30032).

Data Sharing Statement

The authors will share individual deidentified participant data such as blood pressure, side effects and characteristic of CSEA. No other study-related documents will be available. The data will be accessible 6 months after publication from http://www.chictr.org.cn.

Author Contributions

All authors made substantial contributions to conception and design, acquisition of data, analysis and interpretation of data, drafting the manuscript, revising the manuscript critically, read and approve the final draft of the manuscript for submission, gave final approval of the manuscript version to be published and agreed to be accountable for every step of the work.

Disclosure

The authors declare no conflicts of interest.