Prophylactic Ondansetron plus Phenylephrine and Placebo plus Phenylephrine Intravenous Slow Injection on Vasopressor Consumption, Hypotension and Bradycardia after Spinal Anesthesia in Patients Undergoing Cesarean Section: a Randomized, Single-Blind St

Abstract

Introduction: Spinal hypotension (SH) is still the most common complication even though prophylactic phenylephrine is administered. Ondansetron may be the adjunctive drug to prevent SH but the results are controversial. The study aims to compare the vasopressor consumption, incidence of SH and bradycardia between prophylactic ondansetron plus phenylephrine (OP) and placebo plus phenylephrine (PP) group intravenous (IV) slow injection after spinal anesthesia (SA) in cesarean section. Methods: Two hundreds and forty-four patients with BMI <30 kg/m2 undergoing elective cesarean section during January to December 2023 were randomized into two groups; OP (n=122) and PP (n=122). At least 10 min before starting SA, ondansetron 4 mg in 2 ml and NSS 2 ml were administered in group OP and PP, respectively. After finishing SA, both groups were prophylactic administered by IV slow injection of phenylephrine 100 mcg in 10 ml over 30 sec with opening three ways of 3-way stopcock to imitate the function of a smart pump. SH (SBP <90% of baseline) was rescued with phenylephrine 100 mcg. Results: Phenylephrine consumption for SH treatment in both groups had a median of 0 mcg, IQR of 0 to 100 mcg. SH in group OP was lower than group PP (34.4% and 45.9%, respectively). No maternal bradycardia and normal baby Apgar scores were found in both groups. Conclusion: Prophylactic administration of 4 mg ondansetron at least 10 min before SA, along with a slow IV injection of 100 mcg phenylephrine is clinically effective in reducing SH after SA for cesarean section in non-obese parturients.